0000950170-24-020614 | 10-K | XBRL Viewer | Apellis Pharmaceuticals INC

Total future minimum payments

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Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Taxes [Line Items]
Deferred tax asset, increase in valuation allowance	$ 116,900,000
Capitalization of R&D costs	$ 42,300,000	$ 47,600,000
Net operating loss carryforward period	3 years
Interest and penalties	$ 0	0
Accrued for interest and penalties	$ 0	0
Income tax examination description	Generally, the tax years 2020 through 2022 remain open and subject to examination by the major taxing jurisdictions to which the Company is subject.
U.S [Member]
Income Taxes [Line Items]
R&D costs amortization period	5 years
Non - U.S [Member]
Income Taxes [Line Items]
R&D costs amortization period	15 years
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 494,100,000	312,800,000
Research and development tax credit carryforwards	85,700,000
Net operating loss carryforward indefinitely	$ 449,800,000
Net operating loss carryforward expiration year	2025
Research and development tax credit carryforward expiration year	2025
State [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 524,000,000	395,400,000
Research and development tax credit carryforwards	$ 20,200,000
Net operating loss carryforward expiration year	2025
Research and development tax credit carryforward expiration year	2025
Foreign [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	$ 1,663,300,000	$ 1,204,700,000
Net operating loss carryforward expiration year	2027

Development Liability - Schedule of Future Minimum SFJ Payments (Details) - S F J Agreement [Member] - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
2024	$ 98,750
2025	103,000
2026	109,000
2027	55,250
Total future minimum payments	$ 366,000	$ 5,000

Product Revenues, Accounts Receivable, and Reserves for Product Sales

12 Months Ended

Dec. 31, 2023

Product Revenues Accounts Receivable And Reserves For Product Sales [Abstract]

Product Revenues, Accounts Receivable, and Reserves for Product Sales

3. Product Revenues, Accounts Receivable, and Reserves for Product Sales

The Company received FDA approval for the sale of EMPAVELI in the United States in May 2021 and approval for the sale of SYFOVRE in the United States in February 2023. The Company’s product revenues, net of sales discounts and allowances and reserves as of December 31, 2023, 2022 and 2021 totaled $366.3 million, $65.1 million and $15.1 million. The Company’s product revenues consist of sales of EMPAVELI and SYFOVRE to specialty pharmacies and specialty distributors.

The table reflects product revenue by major source for the following periods (in thousands):


	Year Ended December 31,
	2023		2022		2021
Products:
EMPAVELI	$	91,033	$	65,092	$	15,147
SYFOVRE		275,248		—		—
Total product revenue, net	$	366,281	$	65,092	$	15,147

The Company’s accounts receivable balance of $206.4 million as of December 31, 2023 and $7.7 million as of December 31, 2022 primarily consisted of EMPAVELI and SYFOVRE product sales receivable and licensing and other revenue receivables from its collaboration with Sobi. The Company does not have a reserve related to expected credit losses against its accounts receivable balance and expects to collect its accounts receivable in the ordinary course of business.

The Company’s product sales reserves totaled $16.6 million and $2.4 million as of December 31, 2023 and 2022. respectively. These amounts are included in accrued expenses on the Company’s consolidated balance sheet as of December 31, 2023.

The following table summarizes activity in each of the product revenue allowance and reserve categories as of December 31, 2023 (in thousands):


	Chargebacks, Discounts, and Fees			Government and other rebates			Returns			Total
Ending balance at December 31, 2021	$	67		$	716		$	167		$	951
Provision related to sales in the current year		614			4,569			1,185			6,368
Adjustments related to prior period sales		(156	)		(246	)		(385	)		(787	)
Credits and payments made		(362	)		(3,103	)		(716	)		(4,181	)
Ending balance at December 31, 2022	$	164		$	1,936		$	251		$	2,351
Provision related to sales in the current year		17,690			26,661			4,698			49,050
Adjustments related to prior period sales		(112	)		(1,223	)		(2,481	)		(3,817	)
Credits and payments made		(12,068	)		(18,476	)		(415	)		(30,960	)
Ending balance at December 31, 2023	$	5,674		$	8,898		$	2,053		$	16,625

Significant customers - Gross product revenues and product sales receivable from the Company's customers who individually accounted for 10% of more of total gross product revenues and/or 10% or more of total product sales receivable consisted of the following:


	Percent of Total Gross Product Revenues
	Year Ended December 31,
	2023	2022		2021
Customer A	24%	99%		99%
Customer C	16%		—		—
Customer D	54%	1%			—


	Percent of Product Sales Receivable
	As of December 31,
	2023	2022
Customer A	4%	96%
Customer C	22%	3%
Customer D	66%		—

Prepaid and Other Current Assets - Summary of Prepaid Assets and Other Current Assets (Parenthetical) (Details) $ in Millions	1 Months Ended
	Jan. 31, 2024 USD ($)
Subsequent Event [Member]
Prepaid Expense and Other Current Assets [Line Items]
Development cost reimbursement received	$ 15.0

Development Liability - Additional Information (Detail) $ in Thousands		1 Months Ended								8 Months Ended	12 Months Ended
	Feb. 28, 2019 USD ($) Installment	Dec. 31, 2023 USD ($)	May 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	May 31, 2022 USD ($)	Jan. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2021 USD ($) Installment	Jun. 30, 2021 USD ($)	Jan. 31, 2020 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jun. 30, 2019 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Interest expense											$ 29,581	$ 32,626	$ 13,241
SFJ Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from SFJ agreement	$ 60,000
Additional funding amount upon achievement of development milestones	$ 60,000
Number of milestone payments \| Installment	3
Development funding for minimum period of operating expense	10 months
Increase in additional funding for development costs														$ 20,000
Obligated to pay initial payment		$ 366,000					$ 5,000	$ 5,000			366,000		5,000
Aggregate amount of additional annual payments							225,000	$ 225,000					$ 225,000
Number of additional annual payments \| Installment								6
Payment made under agreement						$ 5,000			$ 4,000	$ 80,000	94,000
First annual payment under agreement				$ 18,000	$ 11,500
Second annual payment under agreement		$ 31,000	$ 24,500
Interest expense							$ 1,200				$ 26,000	$ 26,900
SFJ Agreement [Member] \| Regulatory Approval Granted US Food and Drug Administration [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Obligated to pay initial payment	$ 4,000
Aggregate amount of additional annual payments	$ 226,000
Number of additional annual payments \| Installment	6

Income Taxes - Schedule of Reconciliation Between U.S. Federal Statutory Rate and Effective Tax rate, Amount (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Statutory U.S. federal income tax, Amount	$ (110,564)	$ (136,816)	$ (156,660)
Foreign tax rate differential	42,100	50,219	38,677
State income taxes, net of federal benefit, Amount	(13,438)	9,051	(14,145)
Change in valuation allowances, Amount	119,592	94,668	133,668
Tax credits, Amount	(11,566)	(19,966)	(20,005)
Share Based Compensation	(26,881)
Change in state apportionment, Amount		(35)
Loss on debt conversion		6,626	19,548
Permanent and other	2,889	(3,078)	(731)
Total tax expense	$ 2,132	$ 669	$ 352

Equity Incentive Plans

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Equity Incentive Plans

16. Equity Incentive Plans

Share-based Compensation

The Company’s Board of Directors adopted, and its stockholders approved, an equity incentive plan in 2010 (as amended, the “2010 Plan”). The Board of Directors and stockholders amended the 2010 Plan in August 2017 to increase the number of shares of common stock reserved for issuance thereunder to 6,188,466. The 2010 Plan allowed for the grant of incentive stock options and non-qualified stock options to purchase common stock for employees, directors and consultants under terms and conditions established by the Board of Directors. Incentive stock options and nonqualified stock options were granted at exercise prices that were no less than 100% of the estimated fair value per share of the common stock on the date of grant. If an individual owns capital stock representing more than 10% of the voting shares, the price of each share was at least 110% of the fair value on the date of grant. The Board of Directors determined the fair value of common stock with the assistance of a third-party specialist. Options expire 10 years from the issuance date. Following the adoption of the 2017 Stock Incentive Plan, the Company no longer grants stock options or other awards under the 2010 Plan.

In October 2017, the Company’s Board of Directors adopted, and its stockholders approved, the 2017 Stock Incentive Plan (the “2017 Plan”), which became effective on November 8, 2017. The 2017 Plan provides for the grant of incentive stock options, non-statutory stock options, stock appreciation rights, awards of restricted stock, restricted stock units and other stock-based awards. The number of shares of common stock reserved for issuance under the 2017 plan is the sum of (i) 1,359,587 shares of common stock, plus (ii) an additional number of shares of common stock equal to the sum of (a) the number of shares of common stock reserved for issuance under the 2010 equity incentive plan that remained available for future issuance immediately prior to the effectiveness of the 2017 Plan, which was 299,568 shares, and (b) the number of shares of common stock subject to outstanding awards under the 2010 equity incentive plan upon effectiveness of the 2017 plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by us at their original issuance price pursuant to a contractual repurchase right plus (iii) an annual increase, to be added the first day of each fiscal year, beginning with the fiscal year ending December 31, 2018 and continuing until, and including, the fiscal year ending December 31, 2027, equal to the lowest of 4,219,409 shares of common stock, 4.0% of the number of shares of common stock outstanding on the first day of the fiscal year and an amount determined by the board of directors. In January 2024, the shares available for future issuance under the 2017 plan were increased by 4,219,409 shares pursuant to the annual increase described above. As of December 31, 2023, there were 6,497,120 shares available for future grants under the 2017 Plan.

Additionally, since 2019, the Company has granted equity awards as equity inducement awards material to entry into employment with the Company to certain newly hired employees outside of the Company’s existing plans in accordance with Nasdaq listing rule 5635(c)(4). In February 2020, the Board of Directors adopted the 2020 Inducement Stock Incentive Plan (the “2020 Plan”), which permitted the Company to grant equity awards to newly hired employees in accordance with Nasdaq listing rule 5635(c)(4). The aggregate number of shares reserved for issuance under the 2020 Plan was initially 750,000 shares. The Board of Directors amended the 2020 Plan to add 200,000 shares on January 1, 2024, which increased the total number of shares reserved for issuance to 1,950,000 shares as of January 1, 2024. As of December 31, 2023, there were 354,466 shares available for future grants under the 2020 Plan.

In October 2017, the Company’s board of directors adopted, and the Company’s stockholders approved the 2017 Employee Stock Purchase Plan (“ESPP”), which became effective upon the IPO and provides participating employees with the opportunity to purchase up to an aggregate of 468,823 shares of common stock. The number of shares of common stock reserved for issuance under the 2017 ESPP will automatically increase on the first day of each fiscal year, beginning with the fiscal year ending December 31, 2018 and continuing until, and including, the fiscal year ending December 31, 2027, equal to the lowest of (i) 937,646 shares of common stock, (ii) 1.0% of the number of shares of common stock outstanding on the first day of the fiscal year and (iii) an amount determined by the board of directors. The board of directors initiated the first offering under ESPP in October 2019.

The Company has reserved the following shares of common stock for future issuance (in thousands):


	December 31,
	2023		2022		2021
Shares reserved under 2017 Equity Incentive Plan		16,989		14,271		11,014
Shares reserved under 2017 Employee Stock Purchase Plan		553		665		801
Shares reserved under 2020 Inducement Stock Incentive Plan		1,638		1,857		1,761
Total		19,180		16,793		13,576

Total share-based compensation expense related to the various plans during the years ended was as follows (in thousands):


	Year Ended December 31,
	2023		2022		2021
Research and development	$	45,644	$	42,052	$	30,586
General and administrative		60,301		49,033		40,081
Total share-based compensation expense	$	105,945	$	91,085	$	70,667

Stock Options—Options granted generally vest over 48 months. Options granted to employees on or after December 5, 2013 generally vest in installments of (i) 25% at the one-year anniversary and (ii) in either 36 equal monthly or 12 equal quarterly installments beginning in the thirteenth month after the initial vesting commencement date (as defined) subject to the employee’s continuous service with the Company. Options granted before December 5, 2013 vest over four years in equal annual installments of 25% at each anniversary of the grant date.

Under the Executive Separation Benefits and Retention Plan and by resolutions adopted by the Compensation Committee in October 2019, the stock options granted to the Company’s executives and employees will become fully vested upon the occurrence of a change in control, as defined in the Executive Separation Benefits and Retention Plan, if such executive or employee is terminated without cause or resigns for good reason within 12 months after such change in control.

The following table summarizes the Company’s stock option activity:


				Weighted -		Weighted -
				Average		Average		Aggregate
				Exercise		Contractual		Intrinsic
	Shares			Price		Life		Value
	(in thousands)			Per Share		(in years)		(in thousands)
Outstanding, December 31, 2022		12,295		$	26.31		6.24		317,031
Granted		838			52.48
Exercised		(3,950	)		20.11
Forfeited		(519	)		43.65
Outstanding, December 31, 2023		8,664		$	30.65
Options exercisable, December 31, 2023		6,712		$	26.20		5.39	$	226,419
Expected to vest, December 31, 2023		1,952		$	45.97		8.13	$	27,515

The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the fair value of the common stock as of December 31, 2023.

During the years ended December 31, 2023, 2022 and 2021, the Company granted stock options to purchase an aggregate of 0.8 million, 1.3 million and 2.7 million shares of its common stock, respectively with weighted average grant date fair values of $34.26, $23.62 and $30.72, respectively.

The aggregate intrinsic value of options exercised during the years ended December 31, 2023, 2022 and 2021 were $181.0 million, $44.8 million, and $39.9 million respectively calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options on the respective date of exercise.

The fair market value of options vested during the years ended December 31, 2023, 2022 and 2021 were $46.8 million, $59.0 million and $53.2 million, respectively.

On December 31, 2023, unrecognized compensation expense related to unvested options, was $46.1 million, which the Company expects to recognize over an estimated weighted-average period of 2.18 years.

The assumptions used in the Black-Scholes model to estimate the grant date fair value are as follows:


	Year Ended December 31,
	2023	2022	2021
Risk-free interest rate	3.50 - 4.01%	1.15 - 3.37%	0.41 - 1.34%
Dividend yield	0%	0%	0%
Volatility	68.4 - 71.0%	68.3 - 70.4%	71.7 - 74.4%
Expected terms (years)	3.81 - 6.08	3.81 - 6.08	5.31 - 6.08

Restricted Stock Units— The fair value of RSU’s is estimated based upon the closing market price of the Company’s common stock on the date of grant. RSUs generally vest annually over a four-year period.

The following table summarizes the Company’s RSU's activity:


	Number of Stock Units (in thousands)			Weighted Average Grant Date Fair Value Per Share
Unvested Balance at December 31, 2022		3,572		$	42.23
Granted		2,916			52.19
Vested		(1,015	)		41.52
Forfeited		(1,172	)		48.43
Unvested Balance at December 31, 2023		4,301			47.48

The aggregate intrinsic value of restricted grants vested during the year ended December 31, 2023, was $55.3 million. The fair market value of restricted stock units vested during the year ended December 31, 2023 was $42.2 million.

On December 31, 2023, there was approximately $155.5 million of related unrecognized compensation cost which the Company expects to recognize over a remaining weighted average period of 2.6 years.

Employee Stock Purchase Plan—On December 31, 2023, 552,881 shares of common stock remained available for issuance pursuant to the ESPP. Eligible employees who elect to participate in an offering under the ESPP may have up to 15 percent of their earnings withheld, subject to certain limitations, to purchase shares of common stock pursuant to the ESPP. The price of common stock purchased under the ESPP is equal to 85 percent of the lower of the fair market value of the common stock at the commencement date of each offering period or the relevant purchase date. During the year ended December 31, 2023, a total of 112,064 shares of common stock were issued under the ESPP at average per share price of $48.00. During the year ended December 31, 2023, the Company recorded cash received from the issuance of stock to the ESPP of $5.4 million and recorded $2.1 million of stock-based compensation expense related to the ESPP. No additional shares were reserved to the ESPP in 2023.

Leases - Supplemental Cash Flow Information Related to Operating Leases (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Operating cash flows from operating leases	$ 7,939	$ 7,375	$ 5,989
Operating lease assets obtained in exchange for lease obligations	$ 2,700		$ 5,675

Income Taxes - Components of Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current income tax expense:
U.S. State and Local	$ 1,869	$ 520	$ 205
Foreign	263	149	147
Total current income tax expense	2,132	669	352
Deferred income tax expense:
Total tax expense	$ 2,132	$ 669	$ 352

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Long-term Debt - Additional Information (Detail)			1 Months Ended				3 Months Ended		4 Months Ended	12 Months Ended
Long-term Debt - Additional Information (Detail)	May 12, 2020 USD ($)	Sep. 16, 2019 USD ($)	Jul. 31, 2022 USD ($) shares	Jul. 31, 2021 USD ($) shares	Jun. 30, 2021 USD ($) shares	Jan. 31, 2021 USD ($) shares	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2023 USD ($) Days $ / shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($)	Sep. 11, 2019 USD ($) CounterParty $ / shares
Debt Instrument [Line Items]
Aggregate principal amount converted											$ 98,086,000	$ 328,017,000
Loss on conversion of debt											32,890,000	100,589,000
Forfeiture of accrued interest in exchange of convertible notes											1,287,000	4,171,000
Debt interest expense											5,707,000	$ 12,050,000	$ 3,583,000
Amortization of debt issuance costs										$ 297,000	$ 459,000
Long-term debt										$ 93,033,000
Common Stock [Member]
Debt Instrument [Line Items]
Shares issued \| shares											3,073,000	10,065,000
2019 Convertible Notes [Member]
Debt Instrument [Line Items]
Premium paid for capped call transactions												$ 28,400,000
2020 Convertible Notes [Member]
Debt Instrument [Line Items]
Premium paid for capped call transactions												$ 43,100,000
Capped Call Transactions [Member]
Debt Instrument [Line Items]
Number of counterparties \| CounterParty														2
Initial conversion price \| $ / shares														$ 39.4625
Initial cap price \| $ / shares														$ 63.14
Convertible Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt instrument, stated percentage		3.50%
Debt instrument, due and payment description										The Convertible Notes are senior unsecured obligations of the Company and bear interest at a rate of 3.5% per year payable semiannually in arrears on March 15 and September 15 of each year, beginning on March 15, 2020.
Debt instrument, frequency of periodic payment										semiannually
Maturity date		Sep. 15, 2026
Threshold trading days \| Days										20
Threshold consecutive trading days \| Days										30
Threshold percentage of stock price trigger										130.00%
Redemption period, start date										Sep. 20, 2023
Redemption price, percentage										100.00%
Aggregate principal amount converted					$ 700,000				$ 0
Aggregate principal amount converted into shares \| shares					18,775
Long-term debt									92,736,000	$ 93,033,000	$ 92,736,000
Convertible Senior Notes Due 2026 [Member] \| Prior to March 15, 2026 Convertible [Member]
Debt Instrument [Line Items]
Threshold trading days \| Days										20
Threshold consecutive trading days \| Days										30
Threshold percentage of stock price trigger										130.00%
Trading price per principal amount										$ 1,000
Convertible Senior Notes Due 2026 [Member] \| Prior to March 15, 2026 Convertible [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Threshold percentage of stock price trigger										98.00%
Convertible Senior Notes Due 2026 [Member] \| Common Stock [Member]
Debt Instrument [Line Items]
Terms of conversion										The Convertible Notes are convertible into shares of the Company’s common stock at an initial conversion rate of 25.3405 shares per $1,000 principal amount of Convertible Notes (equivalent to an initial conversion price of approximately $39.4625 per share of common stock).
Conversion ratio										0.0253405
Conversion price \| $ / shares										$ 39.4625
Convertible Senior Notes Due 2026 [Member] \| 2019 Convertible Notes [Member]
Debt Instrument [Line Items]
Net proceeds from the sale of the notes		$ 212,900,000
Payment of convertible debt discounts and commissions		6,600,000
Payment of convertible debt offering expenses		500,000
Payments of transactions cost		28,400,000
Debt instrument effective interest rate														10.50%
Debt instrument convertible carrying amount of liability component														$ 145,100,000
Debt discount														74,900,000
Debt issuance costs														7,100,000
Convertible Senior Notes Due 2026 [Member] \| 2019 Convertible Notes [Member] \| Exchange Agreements [Member]
Debt Instrument [Line Items]
Conversion ratio				0.0253405		0.0253405
Debt issuance costs				$ 4,100,000		$ 3,300,000
Increase (decrease) in net debt				197,000,000.0		122,800,000
Aggregate principal amount converted				$ 201,100,000		$ 126,100,000
Increase in shares outstanding \| shares				5,992,217		3,906,869
Shares issued \| shares				5,097,166		3,196,172
Additional shares issued \| shares				895,051		710,697
Additional shares issued for settlement of debt issuance cost paid \| shares				78,419		69,491
Loss on conversion of debt							$ 61,100,000	$ 39,500,000
Loss on conversion of debt related to additional shares issued							55,900,000	36,400,000
Additional amount issued in payment of issuance costs							$ 5,200,000	$ 3,100,000
Forfeiture of accrued interest in exchange of convertible notes						$ 1,700,000
Convertible Senior Notes Due 2026 [Member] \| 2019 Convertible Notes [Member] \| Common Stock [Member] \| Exchange Agreements [Member]
Debt Instrument [Line Items]
Aggregate principal amount converted into shares \| shares						3,906,869
Convertible Senior Notes Due 2026 [Member] \| 2019 Convertible Notes [Member] \| Liability Component [Member]
Debt Instrument [Line Items]
Debt issuance costs														4,700,000
Convertible Senior Notes Due 2026 [Member] \| 2019 Convertible Notes [Member] \| Equity Component [Member]
Debt Instrument [Line Items]
Debt issuance costs														$ 2,400,000
Convertible Senior Notes Due 2026 [Member] \| 2020 Convertible Notes [Member]
Debt Instrument [Line Items]
Net proceeds from the sale of the notes	$ 322,900,000
Payment of convertible debt discounts and commissions	5,700,000
Payment of convertible debt offering expenses	300,000
Payments of transactions cost	$ 43,100,000
Debt instrument effective interest rate	10.50%
Debt instrument convertible carrying amount of liability component	$ 204,500,000
Debt discount	95,500,000
Debt issuance costs	6,000,000.0
Convertible Senior Notes Due 2026 [Member] \| 2020 Convertible Notes [Member] \| Exchange Agreements [Member]
Debt Instrument [Line Items]
Conversion ratio			0.0253405
Debt issuance costs			$ 1,300,000
Increase (decrease) in net debt			96,800,000
Aggregate principal amount converted			$ 98,100,000
Shares issued \| shares			2,485,548
Additional shares issued \| shares			541,470
Additional shares issued for settlement of debt issuance cost paid \| shares			46,132
Loss on conversion of debt			$ 32,900,000
Loss on conversion of debt related to additional shares issued			30,400,000
Additional amount issued in payment of issuance costs			$ 2,500,000
Convertible notes held in treasury									$ 425,400,000	$ 425,400,000	$ 425,400,000
Convertible Senior Notes Due 2026 [Member] \| 2020 Convertible Notes [Member] \| Common Stock [Member] \| Exchange Agreements [Member]
Debt Instrument [Line Items]
Aggregate principal amount converted into shares \| shares			3,027,018	5,992,217
Convertible Senior Notes Due 2026 [Member] \| 2020 Convertible Notes [Member] \| Liability Component [Member]
Debt Instrument [Line Items]
Debt issuance costs	3,700,000
Convertible Senior Notes Due 2026 [Member] \| 2020 Convertible Notes [Member] \| Equity Component [Member]
Debt Instrument [Line Items]
Debt issuance costs	2,300,000
Convertible Senior Notes Due 2026 [Member] \| 2019 and 2020 Convertible Notes [Member] \| Exchange Agreements [Member]
Debt Instrument [Line Items]
Aggregate principal amount converted				$ 201,100,000
Forfeiture of accrued interest in exchange of convertible notes				$ 2,500,000
Convertible Senior Notes Due 2026 [Member] \| Convertible Senior Notes [Member] \| Exchange Agreements [Member]
Debt Instrument [Line Items]
Increase in shares outstanding \| shares			3,027,018
Convertible Senior Notes Due 2026 [Member] \| Private Offering [Member] \| 2019 Convertible Notes [Member]
Debt Instrument [Line Items]
Principal amount		$ 220,000,000.0
Convertible Senior Notes Due 2026 [Member] \| Private Offering [Member] \| 2020 Convertible Notes [Member]
Debt Instrument [Line Items]
Principal amount	$ 300,000,000.0

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 351,185	$ 551,801
Accounts receivable	206,442	7,727
Inventory	146,362	85,714
Prepaid assets	38,820	36,350
Restricted cash	1,114	1,273
Other current assets	22,408	36,658
Total current assets	766,331	719,523
Non-current assets:
Right-of-use assets	16,745	18,747
Property and equipment, net	4,345	6,148
Other assets	1,309	15,799
Total assets	788,730	760,217
Current liabilities:
Accounts payable	37,516	37,342
Accrued expenses	127,806	95,139
Current portion of development liability	75,830	29,504
Current portion of right-of-use liabilities	6,441	5,625
Total current liabilities	247,593	167,610
Long-term liabilities:
Long-term development liability	239,817	315,647
Convertible senior notes	93,033	92,736
Right-of-use liabilities	11,454	14,352
Other liabilities	2,312
Total liabilities	594,209	590,345
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized and zero shares issued and outstanding at December 31, 2023 and 2022	0	0
Common stock, $0.0001 par value; 200,000 shares authorized at December 31, 2023 and 2022; 119,556 and 110,772 shares issued and outstanding at December 31, 2023 and 2022, respectively	12	11
Additional paid-in capital	3,035,539	2,479,596
Accumulated other comprehensive loss	(3,542)	(875)
Accumulated deficit	(2,837,488)	(2,308,860)
Total stockholders’ equity	194,521	169,872
Total liabilities and stockholders’ equity	$ 788,730	$ 760,217

Other Comprehensive Income and Accumulated Other Comprehensive Income - Summary of Changes in Accumulated Other Comprehensive Income/(Loss), by Component (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ 169,872	$ 198,662
Ending balance	194,521	169,872
Unrealized Gains (Losses) from Marketable Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance		1
Net other comprehensive income (loss)		(1)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(2,521)	(2,091)
Net other comprehensive income (loss)	(49)	(430)
Ending balance	(2,570)	(2,521)
Unrealized Gains (Losses) from Pension Plan [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	1,646
Net other comprehensive income (loss)	(2,618)	1,646
Ending balance	(972)	1,646
Total Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(875)	(2,090)
Net other comprehensive income (loss)	(2,667)	1,215
Ending balance	$ (3,542)	$ (875)

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

- Definition

Amount after tax and reclassification adjustments of other comprehensive income (loss).

+ References

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+ Details

- Definition

Amount of equity (deficit) attributable to parent. Excludes temporary equity and equity attributable to noncontrolling interest.

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+ Details

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	1 Months Ended		8 Months Ended	12 Months Ended
	Jan. 31, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jan. 31, 2020 USD ($)	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Number of operating segment \| Segment				1
Inventory				$ 146,362	$ 85,714
SFJ Agreement [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Payment made under agreement	$ 5,000	$ 4,000	$ 80,000	94,000
Regulatory Approval Granted US Food and Drug Administration [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Inventory				$ 19,400

Net Loss per Common Share - Summary of Shares Outstanding that were Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	15,344	18,246	18,651
Convertible Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	2,379	2,379	4,865
Common Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	8,664	12,295	12,562
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	4,301	3,572	1,224

Long-term Debt - Schedule of Interest Expense Recognized Related to Convertible Notes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Interest Expense, Debt [Abstract]
Amortization of debt discount	$ 297	$ 459
Contractual interest expense	$ 3,286	5,248	$ 11,086
Total interest expense		$ 5,707	$ 12,050	$ 3,583

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Components of Loss From Continuing Operation Before Provision for Income Taxes

The components of loss from continuing operations before provision for income taxes are as follows (in thousands):


	Year Ended December 31,
	2023			2022			2021
United States	$	(48,495	)	$	(82,815	)	$	(314,673	)
Foreign		(478,001	)		(568,688	)		(431,329	)
Total	$	(526,496	)	$	(651,503	)	$	(746,002	)

Schedule of Provision for Income Tax Expense

Provision for income taxes for the years ended December 31, 2023, 2022, and 2021 are as follows (in thousands):


	Year Ended December 31, 2023		Year Ended December 31, 2022		Year Ended December 31, 2021
Current income tax expense:
U.S. Federal	$	—	$	—	$	—
U.S. State and Local		1,869		520		205
Foreign		263		149		147
Total current income tax expense		2,132		669		352
Deferred income tax expense:
U.S. Federal		—		—		—
U.S. State and Local		—		—		—
Foreign		—		—		—
Total deferred income tax expense		—		—		—
Total tax expense	$	2,132	$	669	$	352

Schedule of Reconciliation Between U.S. Federal Statutory Rate and Effective Tax rate

A reconciliation between the U.S. federal statutory tax rate and the Company's effective tax rate is summarized as follows (in thousands):


	Year Ended December
	2023						2022						2021
	Amount			Percentage of income before income taxes			Amount			Percentage of income before income taxes			Amount			Percentage of income before income taxes
Statutory U.S. federal income tax	$	(110,564	)		21.0	%	$	(136,816	)		21.0	%	$	(156,660	)		21.0	%
Foreign tax rate differential		42,100			(8.0	)		50,219			(7.7	)		38,677			(5.2	)
State income taxes, net of federal benefit		(13,438	)		2.6			9,051			(1.4	)		(14,145	)		1.9
Change in valuation allowances		119,592			(23.2	)		94,668			(14.5	)		133,668			(17.9	)
Tax credits		(11,566	)		2.2			(19,966	)		3.0			(20,005	)		2.6
Share Based Compensation		(26,881	)		5.1			—			—			—			—
Change in state apportionment		—			—			(35	)		—			—			—
Loss on debt conversion		—			—			6,626			(1.0	)		19,548			(2.6	)
Permanent and other		2,889			(0.1	)		(3,078	)		0.5			(731	)		0.1
Effective income tax provision	$	2,132			(0.4	)	$	669			(0.1	)	$	352			(0.1	)

Schedule of Deferred Tax Assets and Liabilities

The following table presents the principal components of the Company’s deferred tax assets and liabilities (in thousands):


	December 31,
	2023			2022
Deferred tax assets:
Intangible assets	$	192,444		$	187,839
Share-based compensation		31,712			29,673
Net operating loss carryforwards		329,135			228,985
Research and development credits		67,667			57,419
Orphan drug credits		34,023			30,160
Development derivative liability		75,190			79,374
Convertible debt		5,582			6,850
Fixed Assets		18			—
Lease liability		2,888			4,304
Accruals		17,401			16,272
Total deferred tax assets		756,060			640,876
Deferred tax liabilities:
Fixed assets		—			(91	)
Right-of-use asset		(2,672	)		(4,032	)
481(a) adjustment		—			(233	)
Total deferred tax liabilities		(2,672	)		(4,356	)
Net deferred tax assets before allowance:		753,388			636,520
Less valuation allowance		(753,388	)		(636,520	)
Net deferred tax assets	$	—		$	—

Prepaid and Other Current Assets - Additional Information (Details)		1 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($)	Nov. 30, 2022 USD ($)	Dec. 31, 2023 Employees	Dec. 31, 2021
Prepaid Expense and Other Assets, Current [Abstract]
Maximum number of employees with employers eligible for refundable tax credit \| Employees			500
Percentage of qualified wages paid to employees under employee retention credit				70.00%
Maximum credit per employee for each calendar quarter	$ 7,000
Refund filed under CARES Act relating to employee retention credit		$ 8,700,000

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net Income (Loss)	$ (528,628)	$ (652,172)	$ (746,354)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

Inventory - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Inventory Disclosure [Abstract]
Inventory write-downs	$ 6.4	$ 1.5

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”).
Revenue Recognition	Revenue Recognition The Company’s revenues consist of product sales of EMPAVELI and SYFOVRE and revenue derived from its collaboration arrangement with Sobi. See Note 12, License and Collaboration Agreements for further discussion related to the Sobi Collaboration and License Agreement. The Company accounts for contracts with its customers in accordance with ASC Topic 606, Revenue from Contracts with Customers, (“ASC 606”). Pursuant to ASC 606, for arrangements or transactions between participants determined to be within the scope of the contracts with customers guidance, the Company performs the following five steps to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset. For performance obligations that are satisfied over time, the Company recognizes revenue using an input or output measure of progress that best depicts the satisfaction of the relevant performance obligation.
Product Revenue	Product Revenue The Company’s revenue from net product sales was generated in the United States following the FDA’s approval for marketing of EMPAVELI for the treatment of PNH in May 2021 and SYFOVRE in February 2023. The Company sells EMPAVELI and SYFOVRE principally through arrangements with specialty pharmacies (“SPs”) and specialty distributors (“SDs”), who are the Company’s customers. The customers subsequently resell the product to patients and health care providers. The Company applies the ASC 606 five step process discussed above to the contracts with SPs and SDs. The Company provides limited right of return to the customers in cases of shipment errors or expiring or defective products. Product revenues are recognized when the customers take control of the product, which typically occurs upon delivery to the customers. The Company recognizes revenue from product sales at the net sales price which includes estimates of variable consideration for which reserves are established and reflects each of these as a reduction to revenue. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which the Company is entitled based on the terms of the contract. The amount of variable consideration that is included in the transaction price may be constrained. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from estimates, the Company may need to adjust its estimates, which would affect net revenue in the period of adjustment. The following are the Company’s significant categories of variable consideration: Distribution Fees: Distribution fees include distribution service fees paid to SPs and SDs based on a contractually fixed percentage of the wholesale acquisition cost (WAC). The Company does not receive a distinct good or service in exchange for the payment. Distribution fees are recorded as an offset to revenue based on contractual terms at the time revenue from the sale is recognized. Chargebacks: Chargebacks are discounts and fees related to contracts with various third-party payers including pharmacy benefit managers, private healthcare insurers and government healthcare programs that purchase from SDs at a discounted price. SDs charge back to the Company the difference between the price initially paid by SDs and the discounted price paid to SDs by these entities. The Company issues credit notes for the chargeback which are applied to future sales. Product Returns: Consistent with industry practice, the Company offers SPs and SDs limited product return rights for shipment errors or expiring or defective products; provided that the return is within a specified period around the product expiration date as set forth in the applicable individual distribution agreement. The Company does not allow product returns for product that has been dispensed to a patient. As the Company receives inventory reports from SPs and SDs and has visibility into the inventory distribution channel, it is able to make a reasonable estimate of future potential product returns based on this on-hand channel inventory data and sell-through data obtained from SPs and SDs. In arriving at its estimate for product returns, the Company also considers historical product returns (to the extent available), the underlying product demand, and industry data specific to the specialty pharmaceutical distribution industry.
Licensing and Collaboration Revenue	Licensing and Collaboration Revenue The Company analyzes license and collaboration arrangements pursuant to ASC Topic 808, Collaborative Arrangement Guidance and Considerations, (“ASC 808”) to assess whether such arrangements, or transactions between arrangement participants, involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities or are more akin to a vendor-customer relationship. In making this evaluation, the Company considers whether the activities of the collaboration are considered to be distinct and deemed to be within the scope of the collaborative arrangement guidance or if they are more reflective of a vendor-customer relationship and, therefore, within the scope of ASC 606. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For elements of collaboration arrangements that are not accounted for pursuant to guidance in ASC 606, an appropriate recognition method is determined and applied consistently, generally by analogy to the revenue from contracts with customers guidance. Amounts related to transactions with a counterparty in a collaborative arrangement that is not a customer are presented as collaboration revenue and in a separate line item from revenue recognized from contracts with customers, if any, in the consolidated statements of operations. Pursuant to ASC 606, for arrangements or transactions between arrangement participants determined to be within the scope of the contracts with customers guidance, the Company performs the five-step process discussed above to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations. We evaluate the performance obligations promised in the contract that are based on goods and services that will be transferred to the customer and determine whether those obligations are both (i) capable of being distinct and (ii) distinct in the context of the contract. Goods or services that meet these criteria are considered distinct performance obligations. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential transaction price and the likelihood that the transaction price will be received. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and, if so, these options are considered performance obligations. The Company has not currently identified any such material rights. Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset. For performance obligations that are satisfied over time, the Company recognizes revenue using an input or output measure of progress that best depicts the satisfaction of the relevant performance obligation. After contract inception, the transaction price is reassessed at every period end and updated for changes such as resolution of uncertain events. Any change in the overall transaction price is allocated to the performance obligations on the same methodology as at contract inception. See Note 12, License and Collaboration Agreements, for further discussion related to the Sobi collaboration agreement.
Segment Information	Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: development liability, accrued expenses, prepaid expenses, convertible debt, reserves for variable consideration, reserves for excess or obsolete inventories, and income taxes.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company is required to disclose information on the fair value of financial instruments and inputs that enable an assessment of the fair value. The three levels of the fair value hierarchy prioritize valuation inputs based upon the observable nature of those inputs as follows: Level 1 – Quoted prices in active markets for identical assets or liabilities; Level 2 – Inputs other than quoted prices included within level 1 that are observable for the asset or liability, either directly or indirectly; Level 3 – Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. The Company’s financial instruments, in addition to those presented in Note 8, Long-term Debt, and Note 11, Fair Value Measurements, include cash and cash equivalents, accounts payable and accrued liabilities. Management believes that the carrying amounts of cash and cash equivalents, accounts payable and accrued expenses approximate the fair value due to the short-term nature of those instruments.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents are defined as cash in banks and investment instruments having maturities of three months or less from their acquisition date. The carrying amounts reported in the consolidated balance sheets for cash and cash equivalents are valued at cost, which approximates the fair value. See Note 11, Fair Value Measurements, for additional information.
Accounts Receivable	Accounts Receivable The Company’s accounts receivable primarily arise from product sales. They are generally stated at the invoiced amount and do not bear interest. The accounts receivable from product sales represents receivables due from the Company’s SPs or SDs. The Company has had no historical write offs of its accounts receivable as of December 31, 2023, and its payment terms are generally 30-65 days for EMPAVELI and 60-150 days for SYFOVRE. The Company monitors the financial performance and creditworthiness of its customers and provides reserves against trade receivables for expected credit losses that may result from a customer’s inability to pay. Amounts determined to be uncollectible are written-off against the established reserve. As of December 31, 2023 and 2022, the credit profiles for the Company’s customers were deemed to be in good standing and an allowance for credit losses was not considered necessary.
Inventory	Inventory Inventory is recorded at the lower of cost or net realizable value, with cost determined on a first-in, first-out basis. Inventory costs include third-party contract manufacturing, third-party packaging services, and freight. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess and obsolete inventories to their estimated realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded within cost of sales. The determination of whether inventory costs will be realizable requires estimates by management. If actual market conditions are less favorable than projected by management, additional write-downs of inventory may be required which would be recorded as a cost of sales in the consolidated statements of operations and comprehensive loss. Prior to regulatory approval of its product candidates, the Company expensed costs associated with the manufacturing of its product candidates to research and development expense unless the Company was reasonably certain such costs have future commercial use and net realizable value. When the Company believes regulatory approval and subsequent commercialization of its product candidates is probable, and the Company also expects future economic benefit from the sales of the product candidates to be realized, the Company will then capitalize the costs of production as inventory. Inventory that can be used in either the production of clinical or commercial product is expensed as research and development expense when selected for use in a clinical manufacturing campaign. Prior to receiving FDA approval for EMPAVELI on May 14, 2021, the Company included in research and development expense the costs associated with the manufacture of EMPAVELI inventory to be sold upon commercialization. As a result, the manufacturing costs related to the EMPAVELI inventory build-up incurred before FDA approval were expensed in a prior period and are, therefore, excluded from the cost of goods sold and inventory. As of December 31, 2023, the remaining pre-FDA approved inventory was $19.4 million, which primarily consisted of raw materials. Shipping and handling costs for product shipments are recorded as incurred in cost of sales along with costs associated with manufacturing the product and any inventory write-downs.
Development Liability	Development Liability From December 15, 2021 and thereafter until the final annual payment due December 2027, the development liability will be accreted from its initial carrying amount to the total payment amount using the effective interest rate method under ASC 835 over the remaining life of the SFJ agreement as defined in Note 6. The difference between the carrying amount and the total payment amount is presented as discount to the development liability. The accretion is recorded as interest expense in the consolidated income statement.
Foreign Currency	Foreign Currency The functional currency of each of the Company’s subsidiaries is its local currency, except for the wholly owned subsidiaries in Switzerland and Netherlands where the functional currency is the U.S. dollar. Revenues and expenses of the subsidiaries have been translated into U.S. dollars at average exchange rates prevailing during the respective periods. Assets and liabilities have been translated at the rates of exchange on the balance sheet date. The resulting translation gain and loss adjustments are recorded directly as a separate component of stockholders’ equity.
Research and Development	Research and Development Costs incurred in connection with research and development activities are expensed as incurred. Research and development expenses include (i) employee-related expenses, including salaries, benefits, travel and share-based compensation expense; (ii) external research and development expenses incurred under arrangements with third parties, such as contract research and contract manufacturing organizations, investigational sites and consultants, including share-based compensation expense for consultants; (iii) the cost of acquiring, developing and manufacturing clinical study materials; and (iv) costs associated with preclinical and clinical activities and regulatory operations. The Company enters into consulting, research and other agreements with commercial entities, researchers, universities and others for the provision of goods and services. Such arrangements are generally cancellable upon reasonable notice and payment of costs incurred. Costs are considered incurred based on an evaluation of the progress to completion of specific tasks under each contract using information and data provided by the Company’s clinical sites and vendors. These costs consist of direct and indirect costs associated with specific projects, as well as fees paid to various entities that perform certain research on behalf of the Company. Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management’s estimates of the work performed under service agreements, milestones achieved and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly.
Income Taxes	Income Taxes The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided if, based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position, as well as consideration of the available facts and circumstances. As of December 31, 2023 and 2022, the Company did not have any significant uncertain tax positions.
Share Based Compensation - Option	Share-Based Compensation - Options The Company measures stock-based compensation cost at the accounting measurement date based on the fair value of the option and recognizes the expense related to awards to employees on a straight-line basis over the requisite service period of the option, which is typically the vesting period. Forfeitures are recognized as they occur. The Company estimates the fair value of each option using the Black-Scholes option pricing model that considers the fair value of its common stock, the exercise price, the expected life of the option, the expected volatility of its common stock, expected dividends on its common stock, and the risk-free interest rate over the expected life of the option. The Company uses the simplified method described in the SEC's Staff Accounting Bulletin No. 107, Share-Based Payment, to determine the expected life of the option grants. The estimate of expected volatility is based on a review of the historical volatility of similar publicly held companies in the biotechnology field over a period commensurate with the option's expected term. The Company has never declared or paid any cash dividends on its common stock and does not expect to do so in the foreseeable future. Accordingly, it uses an expected dividend yield of zero. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant valuation for a period commensurate with the option's expected term. These assumptions are subjective and changes in them could significantly impact the value of the option and hence the related compensation expense.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk include cash, cash equivalents, and marketable securities. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and the issuers of its cash equivalents and marketable securities. The Company maintains its cash, cash equivalents and marketable securities with highly-rated, federally-insured financial institutions. At times, such amounts may exceed federally-insured limits. The Company has not experienced any losses on its deposits since inception, and management believes that minimal credit risk exists with respect to these financial institutions.
Net Loss per Share	Net Loss per Share Basic net loss per common share is calculated by dividing net loss by the weighted-average shares outstanding during the period. For purposes of the diluted net loss per share calculation, convertible notes and common stock options are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.
Comprehensive Loss	Comprehensive Loss The Company’s components of comprehensive loss other than its net loss, are foreign currency gains/losses recorded from the remeasurement of the long-term intra-entity loan transaction to the Company’s wholly owned subsidiaries, foreign currency gain/loss from the translation of the Company’s wholly owned subsidiaries into U.S. dollars, unrealized gains and losses on marketable securities, and actuarial gains (losses) and prior service costs in connection with the Company's defined benefit plan.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In December 2023, the Financial Accounting Standards Board ("FASB") issued an amendment to the accounting guidance on income taxes which requires entities to provide additional information in the rate reconciliation and additional disaggregated disclosures about income taxes paid. This guidance requires public entities to disclose in their rate reconciliation table additional categories of information about federal, state, and foreign income taxes and to provide more details about the reconciling items in some categories if the items meet a quantitative threshold. The guidance is effective for annual periods beginning after December 15, 2024. The Company is currently evaluating this guidance to determine the impact it may have on its consolidated financial statements disclosures. In November 2023, the FASB issued an amendment to the accounting guidance on segment reporting. The amendments require disclosure of significant segment expenses and other segment items and requires entities to provide in interim periods all disclosures about a reportable segment's profit or loss and assets that are currently required annually. The amendment also requires disclosure of the title and position of the chief operating decision maker ("CODM") and an explanation of how the CODM uses the reported measure(s) of segment profit or loss in assessing segment performance and deciding how to allocate resources. The guidance is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Retrospective application is required, and early adoption is permitted. The Company is currently evaluating the impact the guidance will have on its consolidated financial statements.

Insider Trading Arrangements

3 Months Ended

Dec. 31, 2023

Trading Arrangements, by Individual

Material Terms of Trading Arrangement

The following table describes, for the quarterly period covered by this report, each trading arrangement for the sale or purchase of our securities adopted or terminated by our directors and officers that is either (1) a contract, instruction or written plan intended to satisfy the affirmative defense conditions of Rule 10b5-1(c), or a Rule 10b5-1 trading arrangement, or (2) a “non-Rule 10b5-1 trading arrangement” (as defined in Item 408(c) of Regulation S-K):

      Name (Title)

      Action Taken
 (Date of Action)

      Type of Trading 
Arrangement

      Nature of Trading 
Arrangement

      Duration of Trading 
Arrangement

      Aggregate Number of
 Securities

      Cedric Francois
President and Chief Executive
Officer

      Adoption
 11/30/2023

       Rule 10b5-1 trading arrangement

       Sale

      Until 2/28/2025, or such earlier date upon which all transactions are completed or expire without execution

      Up to 420,000 shares

Nur Nicholson 
Chief Technical Operations

Termination
 12/01/2023

 Rule 10b5-1 trading arrangement

 Sale

(1

)

(1

)

      Timothy E Sullivan
Chief Financial Officer

      Adoption
 12/01/2023

       Rule 10b5-1 trading arrangement

       Sale

      Until 2/28/2025, or such earlier date upon which all transactions are completed or expire without execution

      Up to 150,000 shares

      Pascal Deschatelets
Chief Scientific Officer

      Adoption 
12/03/2023

       Rule 10b5-1 trading arrangement

       Sale

      Until 9/09/2024, or such earlier date upon which all transactions are completed or expire without execution

      Up to 296,028 shares

(1)

This trading plan related to 67,000 shares of our common stock and had a scheduled expiration date of 12/27/2024.

Cedric Francois [Member]

Trading Arrangements, by Individual

Name

Cedric Francois

Title

President and Chief ExecutiveOfficer

Rule 10b5-1 Arrangement Adopted

true

Adoption Date

11/30/2023

Arrangement Duration

457 days

Aggregate Available

420,000

Trd Arr Expiration Date

2/28/2025

Nur Nicholson [Member]

Trading Arrangements, by Individual

Name

Nur Nicholson

Title

Chief Technical Operations

Rule 10b5-1 Arrangement Terminated

true

Termination Date

12/01/2023

Arrangement Duration

393 days

Aggregate Available

67,000

Trd Arr Expiration Date

12/27/2024

Timothy E Sullivan [Member]

Trading Arrangements, by Individual

Name

Timothy E Sullivan

Title

Chief Financial Officer

Rule 10b5-1 Arrangement Adopted

true

Adoption Date

12/01/2023

Arrangement Duration

456 days

Aggregate Available

150,000

Trd Arr Expiration Date

2/28/2025

Pascal Deschatelets [Member]

Trading Arrangements, by Individual

Name

Pascal Deschatelets

Title

Chief Scientific Officer

Rule 10b5-1 Arrangement Adopted

true

Adoption Date

12/03/2023

Arrangement Duration

282 days

Aggregate Available

296,028

Trd Arr Expiration Date

9/09/2024

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenue:
Total product revenue, net	$ 396,591	$ 75,422	$ 66,563
Operating expenses:
Cost of sales	58,510	5,636	200
Research and development	354,387	387,236	345,869
Cost of research collaboration			75,000
License expense			5,000
General and administrative	500,815	277,163	176,771
Total operating expenses:	913,712	670,035	602,840
Net operating loss	(517,121)	(594,613)	(536,277)
Loss on conversion of debt		(32,890)	(100,589)
Loss from remeasurement of development derivative liability			(97,675)
Interest income	20,933	8,914	418
Interest expense	(29,581)	(32,626)	(13,241)
Other(expense)/ income, net	(727)	(288)	1,362
Net loss before taxes	(526,496)	(651,503)	(746,002)
Income tax expense	2,132	669	352
Net loss	(528,628)	(652,172)	(746,354)
Other comprehensive income/(loss):
Unrealized (loss)/gain on marketable securities		(1)	9
Unrealized (loss)/gain on pension plans	(2,618)	1,646
Foreign currency (loss)	(49)	(430)	(1,982)
Total other comprehensive income/(loss)	(2,667)	1,215	(1,973)
Comprehensive loss, net of tax	$ (531,295)	$ (650,957)	$ (748,327)
Net loss per common share, basic	$ (4.45)	$ (6.15)	$ (8.84)
Net loss per common share, diluted	$ (4.45)	$ (6.15)	$ (8.84)
Weighted-average number of common shares used in net loss per common share, basic	118,678	106,114	84,421
Weighted-average number of common shares used in net loss per common share, diluted	118,678	106,114	84,421
Product revenue, net [Member]
Revenue:
Total product revenue, net	$ 366,281	$ 65,092	$ 15,147
Licensing and other revenue [Member]
Revenue:
Total product revenue, net	$ 30,310	$ 10,330	$ 51,416

Net Loss per Common Share - Summary of Basic and Diluted Net Loss per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net Income (Loss)	$ (528,628)	$ (652,172)	$ (746,354)
Denominator:
Weighted-average number of common shares used in net loss per common share, basic	118,678	106,114	84,421
Weighted-average number of common shares used in net loss per common share, diluted	118,678	106,114	84,421
Net loss per common share, basic	$ (4.45)	$ (6.15)	$ (8.84)
Net loss per common share, diluted	$ (4.45)	$ (6.15)	$ (8.84)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Inventory (Tables)

12 Months Ended

Dec. 31, 2023

Inventory Disclosure [Abstract]

Schedule Of Inventory Current

The Company’s inventory of EMPAVELI and SYFOVRE consisted of the following as of December 31, 2023, and December 31, 2022 (in thousands):


	December 31,
	2023		2022
Raw materials	$	32,724	$	29,847
Semi-finished goods		82,924		54,101
Finished goods		30,714		1,766
Total inventories	$	146,362	$	85,714

Inventory amounts written down as a result of excess, obsolete, unmarketability or other reasons are charged to cost of sales. For the years ended December 31, 2023 and 2022, the Company recognized write-downs of $6.4 million and $1.5 million, respectively.

Nature of Organization and Operations

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Nature of Organization and Operations

1. Nature of Organization and Operations

Apellis Pharmaceuticals, Inc. (the “Company”) is a commercial-stage biopharmaceutical company focused on the discovery, development and commercialization of novel therapeutic compounds to treat diseases with high unmet needs through the inhibition of the complement system, which is an integral component of the immune system, at the level of C3, the central protein in the complement cascade.

The Company was incorporated in September 2009 under the laws of the State of Delaware. The Company’s principal executive offices are located in Waltham, Massachusetts.

The Company’s operations since inception have been limited to organizing and staffing the Company, acquiring rights to product candidates, business planning, raising capital, developing its product candidates, commercializing EMPAVELI (pegcetacoplan) for the treatment of paroxysmal nocturnal hemoglobinuria (“PNH”) and commercializing SYFOVRE (pegcetacoplan injection) for the treatment of geographic atrophy secondary to age-related macular degeneration (“GA”).

The Company is subject to risks common in the biotechnology industry including, but not limited to, raising additional capital, development by its competitors of new technological innovations, its ability to successfully complete preclinical and clinical development of product candidates and receive timely regulatory approval of products, market acceptance of the Company’s products, protection of proprietary technology, healthcare cost containment initiatives, and compliance with governmental regulations, including those of the U.S. Food and Drug Administration (“FDA”).

Follow-on Public Offerings

On February 22, 2023, the Company issued and sold 4,007,936 shares of common stock and, in lieu of common stock to investor who so chose, pre-funded warrants to purchase 2,380,956 shares of common stock in a follow-on offering, including 833,333 shares sold pursuant to the underwriters’ exercise in full of their option to purchase additional shares of common stock. The price to the public of the shares of common stock was $63.00 per share and the price to the public of the pre-funded warrants was $62.9999 per pre-funded warrant. The pre-funded warrants have an exercise price equal to $0.0001 per share and do not expire. The pre-funded warrants were accounted for as equity instruments. The Company received total net proceeds of $384.4 million, after deducting underwriting discounts and commissions of $18.8 million and offering costs of $0.3 million.

On March 28, 2022, the Company issued and sold 8,563,830 shares of its common stock at a price per share to the public of $47.00 in a follow-on public offering including an additional 1,117,021 shares of its common stock that were sold at the follow-on public offering price of $47.00 per share pursuant to the underwriters’ agreement in full exercise of their option to purchase additional shares of common stock. The Company received net proceeds of approximately $380.1 million after deducting underwriting discounts and commissions of approximately $22.1 million and offering costs of $0.3 million for these transactions.

On November 18, 2021, the Company issued and sold 10,062,500 shares of its common stock at a price per share to the public of $40.00 in a follow-on public offering including an additional 1,312,500 shares of its common stock that were sold at the follow-on public offering price of $40.00 per share pursuant to the underwriters’ agreement in full exercise of their option to purchase additional shares of common stock. The Company received net proceeds of approximately $380.4 million after deducting underwriting discounts and commissions of approximately $22.1 million and offering costs of $0.6 million for these transactions.

Liquidity and Going Concern

The accompanying consolidated financial statements have been prepared assuming that the Company will continue as a going concern. From inception to December 31, 2023, the Company has incurred cash outflows from operations, losses from operations, and had an accumulated deficit of $2.8 billion, primarily as a result of expenses incurred through a combination of research and development activities related to the Company’s various product candidates and expenses supporting those activities. The Company has primarily financed its operations through public offerings of its common stock, convertible debt, private placements of preferred stock prior to its initial public offering, the development funding agreement with SFJ, and the collaboration agreement with Sobi. The Company has financed a portion of its operations through product sales but has not yet achieved profitability.

The Company believes that its cash and cash equivalents of $351.2 million at December 31, 2023 and the cash anticipated to be generated from the unwind of the capped call transactions, together with cash anticipated to be generated from sales of EMPAVELI and from SYFOVRE will be sufficient to fund its operations and capital expenditure requirements for at least twelve months from the date of issuance of these consolidated financial statements.

Fair Value Measurements - Schedule of Financial Instruments and the Related Fair Value Hierarchy of the Valuation Techniques Utilized (Detail) - Fair Value, Nonrecurring [Member] - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 276,391	$ 527,728
Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	276,391	527,728
Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	276,391	527,728
Level 1 [Member] \| Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 276,391	$ 527,728

Accrued Expenses

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Accrued Expenses

7. Accrued Expenses

Accrued expenses consisted of the following as of December 31, 2023, and December 31, 2022 (in thousands):


	December 31,
	2023		2022
Accrued research and development	$	28,318	$	34,849
Accrued royalties		10,197		907
Accrued payroll liabilities		51,781		43,212
Product revenue reserves		16,625		2,351
Other		20,885		13,820
Total accrued expenses	$	127,806	$	95,139

Prepaid and Other Current Assets (Tables)

12 Months Ended

Dec. 31, 2023

Prepaid Expense and Other Assets, Current [Abstract]

Summary of Prepaid Assets and Other Current Assets

Prepaid assets and other current assets consisted of the following as of December 31, 2023, and December 31, 2022 (in thousands):


	December 31,
	2023		2022
Down payments for inventory	$	16,296	$	13,987
Prepaid research and development		13,931		15,181
Other prepaid expenses		8,593		7,182
Total prepaid expenses	$	38,820	$	36,350


	December 31,
	2023		2022
Royalties receivable		3,054	$	1,442
ERC credit		—		8,711
Receivable from collaboration agreement (1)		15,000		20,000
Deposits and other current assets		4,354		6,505
Total other current assets	$	22,408	$	36,658

(1)

In January 2024 the Company waived the remaining reimbursement payment of $15.0 million in connection with the decision to discontinue the CAD program.

Equity Incentive Plans - Summary of Shares of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Feb. 29, 2020
Class Of Stock [Line Items]
Common stock reserved for future issuance	19,180,000	16,793,000	13,576,000
2017 Stock Incentive Plan [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	16,989,000	14,271,000	11,014,000
2017 Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	553,000	665,000	801,000
2020 Inducement Stock Incentive Plan [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	1,638,000	1,857,000	1,761,000	750,000

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value, Nonrecurring [Member]

Schedule of Financial Instruments and the Related Fair Value Hierarchy of the Valuation Techniques Utilized

The following table presents the fair value of financial instruments recorded originally at amortized cost or fair value and not re-measured on a recurring basis (in thousands):


		December 31, 2023
Balance Sheet Classification:	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents:	Money market funds	$	276,391	$	—	$	—	$	276,391
Total Financial Assets		$	276,391	$	—	$	—	$	276,391

		December 31, 2022
Balance Sheet Classification:	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents:	Money market funds	$	527,728	$	—	$	—	$	527,728
Total Financial Assets		$	527,728	$	—	$	—	$	527,728

Equity Incentive Plans - Summary of Assumption Used to Estimate the Grant Date Fair Value (Detail)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate, minimum	3.50%	1.15%	0.41%
Risk-free interest rate, maximum	4.01%	3.37%	1.34%
Dividend yield	0.00%	0.00%	0.00%
Volatility, minimum	68.40%	68.30%	71.70%
Volatility, maximum	71.00%	70.40%	74.40%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected terms (years)	3 years 9 months 21 days	3 years 9 months 21 days	5 years 3 months 21 days
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected terms (years)	6 years 29 days	6 years 29 days	6 years 29 days

Other Comprehensive Income and Accumulated Other Comprehensive Income

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Other Comprehensive Income and Accumulated Other Comprehensive Income

10. Other Comprehensive Income and Accumulated Other Comprehensive Income

The following tables summarize the changes in accumulated other comprehensive income/(loss), by component for the years ended December 31, 2023 and 2022 (in thousands):


	Unrealized Gains (Losses) from Marketable Securities			Foreign Currency Translation Adjustment			Unrealized Gains (Losses) from Pension Plan			Total Accumulated Other Comprehensive Income (Loss)
Balances, December 31, 2022	$	—		$	(2,521	)	$	1,646		$	(875	)
Net other comprehensive income (loss)		—			(49	)		(2,618	)	$	(2,667	)
Balances, December 31, 2023	$	—		$	(2,570	)	$	(972	)	$	(3,542	)


	Unrealized Gains (Losses) from Marketable Securities			Foreign Currency Translation Adjustment			Unrealized Gains (Losses) from Pension Plan			Total Accumulated Other Comprehensive Income (Loss)
Balances, December 31, 2021	$	1		$	(2,091	)	$	—		$	(2,090	)
Net other comprehensive income (loss)		(1	)		(430	)		1,646		$	1,215
Balances, December 31, 2022	$	—		$	(2,521	)	$	1,646		$	(875	)

Product Revenues, Accounts Receivable, and Reserves for Product Sales (Tables)

12 Months Ended

Dec. 31, 2023

Product Revenues Accounts Receivable And Reserves For Product Sales [Abstract]

Schedule of Disaggregation of Product Revenue by Major Source

The table reflects product revenue by major source for the following periods (in thousands):


	Year Ended December 31,
	2023		2022		2021
Products:
EMPAVELI	$	91,033	$	65,092	$	15,147
SYFOVRE		275,248		—		—
Total product revenue, net	$	366,281	$	65,092	$	15,147

Summary of Product Revenue Allowance and Reserve Categories

The following table summarizes activity in each of the product revenue allowance and reserve categories as of December 31, 2023 (in thousands):


	Chargebacks, Discounts, and Fees			Government and other rebates			Returns			Total
Ending balance at December 31, 2021	$	67		$	716		$	167		$	951
Provision related to sales in the current year		614			4,569			1,185			6,368
Adjustments related to prior period sales		(156	)		(246	)		(385	)		(787	)
Credits and payments made		(362	)		(3,103	)		(716	)		(4,181	)
Ending balance at December 31, 2022	$	164		$	1,936		$	251		$	2,351
Provision related to sales in the current year		17,690			26,661			4,698			49,050
Adjustments related to prior period sales		(112	)		(1,223	)		(2,481	)		(3,817	)
Credits and payments made		(12,068	)		(18,476	)		(415	)		(30,960	)
Ending balance at December 31, 2023	$	5,674		$	8,898		$	2,053		$	16,625

Schedule of Customer Accounted for 10% of More of Gross Product Revenues and Accounts Receivable


	Percent of Total Gross Product Revenues
	Year Ended December 31,
	2023	2022		2021
Customer A	24%	99%		99%
Customer C	16%		—		—
Customer D	54%	1%			—


	Percent of Product Sales Receivable
	As of December 31,
	2023	2022
Customer A	4%	96%
Customer C	22%	3%
Customer D	66%		—

Employee Retirement Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Tax Status [Extensible Enumeration]	us-gaap:QualifiedPlanMember	us-gaap:QualifiedPlanMember	us-gaap:QualifiedPlanMember
Minimum age of full-time employees eligible to participate in the plan	21 years
Employer contributions made to the 401(k) Plan	$ 5,700,000	$ 4,300,000	$ 3,100,000
Swiss Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Funded status	2,200,000	18,000
Fair value of plan assets	16,200,000	12,900,000
Projected benefit obligation	18,400,000	12,900,000
Accumulated benefit obligation	2,600,000	1,600,000
Net periodic benefit cost	$ 900,000	$ 600,000

Commitments and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

15. Commitments and Contingencies

The Company has certain non-cancelable purchase obligations related to the manufacturing of drug substance and drug product, with Bachem Americas, Inc., under which the Company has agreed to purchase a significant portion of its requirements for the pegcetacoplan drug substance over the next five years and a commercial supply agreement with NOF Corporation, under which the Company has agreed to purchase activated polyethylene glycol derivative, or PEG, which is a component of pegcetacoplan. Under these agreements, as of December 31, 2023, the Company is obligated to pay up to an aggregate of $94.6 million to these vendors. In addition, the Company has other non-cancelable purchase agreements as of December 31, 2023, under which it is obligated to pay up to $16.1 million to vendors.

The Company is a party to a master lease agreement under which the Company leases vehicles with initial terms of 36 months from the date of delivery. If the Company were unable to take delivery of a previously ordered vehicle, the Company may incur nominal fees.

Indemnifications—In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend indemnified parties for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third-party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has not incurred any cost to defend lawsuits or settle claims related to these indemnification provisions.

Legal—During the normal course of business, the Company may be a party to legal claims that may not be covered by insurance. The Company cannot predict the outcome of the litigation described in Item 3 with certainty. The Company intends to defend vigorously against this litigation.

Equity Incentive Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		12 Months Ended
	Jan. 01, 2024	Oct. 31, 2017	Aug. 31, 2017	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jan. 31, 2024	Feb. 29, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance				19,180,000	16,793,000	13,576,000
Stock options vesting period				48 months
Stock options vesting description				Options granted to employees on or after December 5, 2013 generally vest in installments of (i) 25% at the one-year anniversary and (ii) in either 36 equal monthly or 12 equal quarterly installments beginning in the thirteenth month after the initial vesting commencement date (as defined) subject to the employee’s continuous service with the Company.
Aggregate number of stock options granted to purchase common stock				838,000	1,300,000	2,700,000
Weighted - Average Grant Date Fair Value Per Option, Granted				$ 34.26	$ 23.62	$ 30.72
Aggregate intrinsic value of options exercised in period				$ 181,000	$ 44,800	$ 39,900
Fair market value of options vested in period				46,800	$ 59,000	53,200
Unrecognized compensation expense				$ 46,100
Estimated weighted-average period to recognize				2 years 2 months 4 days
Common stock, issued				119,556,000	110,772,000
Common stock issued at average per share price				$ 20.11
Share-based compensation expense				$ 105,945	$ 91,085	$ 70,667
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense				$ 155,500
Estimated weighted-average period to recognize				2 years 7 months 6 days
Aggregate intrinsic value of restricted grants vested				$ 55,300
Fair market value of restricted stock units vested				$ 42,200
Frist Anniversary [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting percentage				25.00%
Second Anniversary [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting percentage				25.00%
Third Anniversary [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting percentage				25.00%
Fourth Anniversary [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting percentage				25.00%
Subsequent Event [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issuable increased during the period	200,000
Equity Incentive Plan 2010 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares reserved for issuance			6,188,466
Percentage of voting shares			10.00%
Options expire from issuance date			10 years
Equity Incentive Plan 2010 [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of estimated fair value per share of common stock on the date of grant			100.00%
Equity Incentive Plan 2010 [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage price of each share of the fair value on date of grant			110.00%
2017 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares reserved for issuance		1,359,587
Percentage of voting shares		4.00%
Number of shares available for future grant		299,568		6,497,120
Shares issuable increased during the period		4,219,409
Common Stock Issuance Description				equal to the lowest of 4,219,409 shares of common stock, 4.0% of the number of shares of common stock outstanding on the first day of the fiscal year and an amount determined by the board of directors.
Common stock reserved for future issuance				16,989,000	14,271,000	11,014,000
2017 Stock Incentive Plan [Member] \| Subsequent Event [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant							4,219,409
2020 Inducement Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant				354,466
Common stock reserved for future issuance				1,638,000	1,857,000	1,761,000		750,000
2020 Inducement Stock Incentive Plan [Member] \| Subsequent Event [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant	1,950,000
2017 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares reserved for issuance		468,823
Percentage of voting shares				1.00%
2017 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance				937,646
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage price of each share of the fair value on date of grant				85.00%
Number of shares available for future grant				552,881
Common stock reserved for future issuance				0
Percentage of earnings withheld to purchase shares of common stock				15.00%
Common stock, issued				112,064
Common stock issued at average per share price				$ 48
Cash received from issuance of purchase rights				$ 5,400
Share-based compensation expense				$ 2,100

Long-term Debt

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Long-term Debt

8. Long-term Debt

Convertible Senior Notes

On September 16, 2019, the Company completed a private offering of the 2019 Convertible Notes with an aggregate principal amount of $220.0 million issued pursuant to an indenture (the “Indenture”) with U.S. Bank National Association, as trustee (the “Trustee”).

The net proceeds from the sale of the 2019 Convertible Notes were approximately $212.9 million after deducting the initial purchasers’ discounts and commissions of $6.6 million and offering expenses of $0.5 million paid by the Company. The Company used $28.4 million of the net proceeds from the sale of the Convertible Notes to pay the cost of the capped call transactions described below.

On May 12, 2020, the Company issued the 2020 Convertible Notes with an aggregate principal amount of $300.0 million. The net proceeds from the sale of the 2020 Convertible Notes were approximately $322.9 million after deducting the purchasers’ discounts and commission of $5.7 million and offering expenses of $0.3 million. The Company used $43.1 million of the net proceeds from the sale to pay the cost of the additional capped call transactions in May 2020 described below.

The 2019 Convertible Notes and the 2020 Convertible Notes are referred to together as the Convertible Notes. The Convertible Notes are senior unsecured obligations of the Company and bear interest at a rate of 3.5% per year payable semiannually in arrears on March 15 and September 15 of each year, beginning on March 15, 2020. The Convertible Notes will mature on September 15, 2026, unless converted earlier, redeemed or repurchased in accordance with their terms.

The Convertible Notes are convertible into shares of the Company’s common stock at an initial conversion rate of 25.3405 shares per $1,000 principal amount of Convertible Notes (equivalent to an initial conversion price of approximately $39.4625 per share of common stock). The conversion rate is subject to customary anti-dilution adjustments. In addition, following certain events that occur prior to the maturity date or if the Company deliver a notice of redemption, the Company will increase the conversion rate for a holder who elects to convert its Convertible Notes in connection with such corporate event or a notice of redemption, as the case may be, in certain circumstances as provided in the indenture.

Prior to March 15, 2026, the Convertible Notes are convertible only upon the occurrence of certain events:

•

during any calendar quarter, if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day;

•

during the five-business day period after any five consecutive trading day period in which the trading price per $1,000 principal amount of the Convertible Notes for each such trading day was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such trading day;

•

if the Company calls any or all of the Convertible Notes for redemption, at any time prior to the close of business on the second scheduled trading day immediately preceding the redemption date; or

•

upon the occurrence of corporate events specified in the Indenture.

On or after March 15, 2026 until the close of business on the second scheduled trading day immediately preceding the maturity date of the Convertible Notes, holders may convert the Convertible Notes at any time. Upon conversion of the Convertible Notes, the Company will pay or deliver, as the case may be, cash, shares of the Company’s common stock or a combination of cash and shares of common stock, at the Company’s election.

Prior to September 20, 2023, the Company could not redeem the Convertible Notes. From and after September 20, 2023, the Company may redeem for cash all or a portion of the Convertible Notes, at its option, if the last reported sale price of the Company’s common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive), including the trading day immediately preceding the date on which the Company provides a notice of redemption, during any 30 consecutive trading day period ending on, and including, the trading day immediately preceding the date on which the Company provides notice of redemption. The redemption price will be equal to 100% of the principal amount of the Convertible Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. If the Company calls any Convertible Notes for redemption, it will constitute a “make-whole fundamental change” with respect to such Convertible Notes, in which case the conversion rate applicable to the conversion of such Notes, if converted in connection with the redemption, will be increased in certain circumstances. The Company has not called for redemption or redeemed any of the Convertible Notes as of December 31, 2023.

If the Company undergoes a “fundamental change,” as defined in the Indenture, prior to maturity, subject to certain conditions, holders may require the Company to repurchase for cash all or any portion of their Convertible Notes at a fundamental change repurchase price equal to 100% of the principal amount of the notes to be repurchased, plus any accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

The Company used an effective interest rate of 10.5% to determine the liability component of the 2019 and 2020 Convertible Notes. This resulted in the recognition of $145.1 million and $204.5 million as the liability component of the 2019 and 2020 Convertible Notes, respectively, and the recognition of the residual amount of $74.9 million and $95.5 million as the debt discount with a corresponding increase to additional paid in capital for the equity component of the 2019 and 2020 Convertible Notes, respectively. The 2020 aggregate debt issuance costs of $6.0 million were allocated to the liability and equity components in the amounts of $3.7 million and $2.3 million, respectively. The 2019 Convertible Notes aggregate debt issuance costs of $7.1 million were allocated to the liability and equity components in the amounts of $4.7 million and $2.4 million, respectively.

In January 2021, July 2021 and July 2022, the Company entered into separate, privately negotiated exchange agreements to modify the conversion terms with certain holders of its 2019 Convertible Notes and 2020 Convertible Notes. Under the terms of these exchange agreements, in January 2021, July 2021 and July 2022, the holders exchanged approximately $126.1 million of 2019 Convertible Notes, $201.1 million of 2019 Convertible Notes and 2020 Convertible Notes, and $98.1 million of 2020 Convertible Notes, respectively, in aggregate principal amount held by them for an aggregate of 3,906,869 shares, 5,992,217 shares and 3,027,018 shares, respectively, of common stock issued by the Company. In accordance with ASC Topic 470-20, “Debt – Debt with Conversion and Other Options,” (“ASC 470-20”) the Company accounted for the exchange as an induced conversion based on the short period of time the conversion offer was open and the substantive conversion feature offer. The Company accounted for the conversion of the debt as an inducement by expensing the fair value of the shares that were issued in excess of the original terms of the Convertible Notes.

As a result of the January 2021 exchange transactions, the Company reduced net debt outstanding and increased net equity on the consolidated balance sheet by $122.8 million, consisting of the par value of the 2019 Convertible Notes exchanged of $126.1 million less the $3.3 million of remaining debt issuance costs associated with the exchanged notes. The Company also increased shares outstanding by 3,906,869 shares consisting of 3,196,172 shares issued at the initial conversion rate in the Indenture of 25.3405 plus an additional 710,697 shares. Additionally, the Company issued 69,491 shares as settlement of debt issuance costs paid to the Company’s financial advisor in connection with the exchange transaction. For the three months ended March 31, 2021, the Company recorded a loss on conversion of debt of $39.5 million comprised of $36.4 million related to the value of the shares issued in excess of the original conversion terms at the fair market value and $3.1 million for the value of the 69,491 shares issued in payment of issuance costs at their then fair value. Upon exchange of the 2019 Convertible Notes, the holders forfeited accrued interest through the date of the exchange of $1.7 million, which the Company charged to interest expense and to equity.

As a result of the July 2021 exchange transactions, the Company reduced net debt outstanding and increased net equity on the consolidated balance sheet by $197.0 million, consisting of the par value of the Convertible Notes exchanged of $201.1 million less the $4.1 million of remaining debt issuance costs associated with the exchanged notes. The Company also increased shares outstanding by 5,992,217 shares consisting of 5,097,166 shares issued at the initial conversion rate in the Indenture of 25.3405 plus an additional 895,051 shares. Additionally, the Company issued 78,419 shares as settlement of issuance costs paid to the Company’s financial advisor in connection with the exchange transaction. For the three months ended September 30, 2021, the Company recorded a loss on conversion of debt of $61.1 million comprised of $55.9 million related to the value of the shares issued in excess of the original conversion terms at the fair market value and $5.2 million for the value of the 78,419 shares issued in payment of issuance costs at their then fair value. Upon exchange of the Convertible Notes, the holders forfeited accrued interest through the date of the exchange of $2.5 million, which the Company charged to interest expense and to equity.

As a result of the July 2022 exchange transactions, the Company reduced net debt outstanding and increased net equity on the consolidated balance sheet by $96.8 million, consisting of the par value of the Convertible Notes exchanged of $98.1 million less the $1.3 million of remaining debt issuance costs associated with the exchanged notes. The Company also increased shares outstanding by 3,027,018 shares consisting of 2,485,548 shares issued at the initial conversion rate in the Indenture of 25.3405 plus an additional 541,470 shares. Additionally, the Company issued 46,132 shares as settlement of issuance costs paid to the Company’s financial advisor in connection with the exchange transaction. The Company recorded a loss on conversion of debt of $32.9 million comprised of $30.4 million related to the value of the shares issued in excess of the original conversion terms at the fair market value and $2.5 million for the value of the 46,132 shares.

The conditional conversion feature of the Convertible Notes was triggered as of June 30, 2021, and as a result the Convertible Notes were convertible at the option of the holders until September 30, 2021. During this period, certain holders of the Convertible Notes converted approximately $0.7 million of aggregate principal amount of Convertible Notes into an aggregate of 18,775 shares, which were issued in October 2021.

The conditional conversion feature of the Convertible Notes was again triggered as of September 30, 2022, and as a result the Convertible Notes became convertible at the option of the holders until December 31, 2022. No Convertible Notes were converted during this period.

The conditional conversion feature of the Convertible Notes was triggered as of December 31, 2023, and as a result the Convertible Notes are convertible at the option of the holders until March 31, 2024.

As of December 31, 2023 and 2022, the Company held in treasury Convertible Notes in principal amount of $425.4 million which have not been cancelled.

The outstanding balance of the Convertible Notes as of December 31, 2023 and 2022 consisted of the following (in thousands):


	December 31,
	2023			2022
Liability
Principal		93,897			93,897
Less: debt discount and issuance costs, net		(864	)		(1,161	)
Net carrying amount		93,033			92,736

The following table sets forth total interest expense recognized related to the Convertible Notes during the twelve months ended December 31, 2023, 2022 and 2021 (in thousands):


	Year Ended December 31,
		2023		2022		2021
Amortization of debt issuance costs			297		459		964
Contractual interest expense			3,286		5,248		11,086
Total interest expense		$	3,583	$	5,707	$	12,050

Future minimum payments on Convertible Notes payable as of December 31, 2023 is as follows (in thousands):


2024	$	3,286
2025		3,286
2026		96,225
Total future minimum payments		102,797
Less: interest		(8,900	)
Less: debt discount and issuance costs, net		(864	)
Less: current portion		—
Convertible senior notes		93,033

Capped Call Transactions

On September 11, 2019, and May 6, 2020 concurrently with the pricing of the 2019 Convertible Notes and the 2020 Convertible Notes, the Company entered into capped call transactions with two counterparties. The capped call transactions are expected generally to reduce the potential dilution to the Company’s common stock upon any conversion of Convertible Notes and/or offset any cash payments the Company is required to make in excess of the principal amount of converted Convertible Notes, as the case may be, in the event that the market price per share of the Company’s common stock, as measured under the terms of the capped call transactions, is greater than the strike price of the capped call transactions, which is initially $39.4625 (the conversion price of the Convertible Notes) and is subject to anti-dilution adjustments substantially similar to those applicable to the conversion rate of such Convertible Notes. If, however, the market price per share of the Company’s common stock, as measured under the terms of the capped call transactions, exceeds the cap price of the capped call transactions, which is initially $63.14 per share, there would nevertheless be dilution and/or there would not be an offset of such potential cash payments, in each case, to the extent that such market price exceeds the cap price of the capped call transactions.

Pursuant to ASC 815-40 Derivatives and Hedging, the Company determined that the capped call transactions should be classified as equity instruments and the capped call premium paid in the amount of $28.4 million and $43.1 million were recorded as reductions to additional paid-in capital at December 31, 2021 for the 2019 and 2020 Convertible Notes, respectively

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 470
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//470/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

+ Details

Product Revenues, Accounts Receivable, and Reserves for Product Sales - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Total product revenue, net	$ 396,591	$ 75,422	$ 66,563
Accounts receivable	206,442	7,727
Accrued Expenses [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Product sales reserves	16,600	2,400
Product revenue, net [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Total product revenue, net	$ 366,281	$ 65,092	$ 15,147

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 924
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479941/924-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 40
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-40

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 41
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-41

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-4

+ Details

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Activities
Net loss	$ (528,628)	$ (652,172)	$ (746,354)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	105,945	91,085	70,667
Loss on conversion of debt		32,890	100,589
Loss from remeasurement of development derivative liability			97,675
Loss on disposal of fixed assets	120
Forfeiture of accrued interest in exchange of convertible notes		1,287	4,171
Depreciation expense	1,784	1,552	1,379
Amortization of right of use assets	(80)	(65)	113
Amortization of discounts for convertible notes, net of financing costs	297	459	964
Accretion of discount to development liability	25,996	26,917	1,192
Changes in operating assets and liabilities:
Accounts receivable	(198,715)	2,375	(10,103)
Inventory	(60,647)	(69,397)	(16,317)
Prepaid assets	(1,870)	(11,479)	(13,487)
Other current assets	14,243	32,936	(40,928)
Other assets	11,700	17,490	(12,782)
Accounts payable	170	18,689	10,487
Accrued expenses	34,950	(6,312)	(10,392)
Net cash used in operating activities	(594,735)	(513,745)	(563,126)
Investing Activities
Purchase of property and equipment	(773)	(1,524)	(1,103)
Proceeds from sale of fixed assets	99
Purchase of available-for-sale securities		(331,863)	(171,281)
Proceeds from maturity of available-for-sale securities		393,280	420,000
Net cash (used in) provided by investing activities	(674)	59,893	247,616
Financing Activities
Proceeds from issuance of common stock, net of issuance costs		380,120	380,363
Proceeds from issuance of common stock, pre-funded warrant offering, net of issuance costs	384,387
Payments for development derivative liability			(4,000)
Payments for development liability	(55,500)	(34,500)
Proceeds from exercise of stock options	71,274	21,483	14,691
Proceeds from issuance of common stock under employee share purchase plan	5,378	4,238	2,970
Payments of employee tax withholding related to equity-based compensation	(11,040)	(5,682)	(1,788)
Net cash provided by financing activities	394,499	365,659	392,236
Effect of exchange rate changes on cash and cash equivalents	135	(488)	(2,016)
Net (decrease) increase in cash and cash equivalents	(200,775)	(88,681)	74,710
Cash, cash equivalents and restricted cash at beginning of period	553,074	641,755	567,045
Cash, cash equivalents and restricted cash at end of period	352,299	553,074	641,755
Reconciliation of cash, cash equivalents and restricted cash to the consolidated balance sheets:
Cash and cash equivalents	351,185	551,801	640,192
Restricted cash	1,114	1,273	1,563
Total cash, cash equivalents, and restricted cash	352,299	553,074	641,755
Supplemental disclosure of cash flow information:
Cash paid for interest	3,286	5,003	10,265
Cash paid for income taxes		4,915	49
Proceeds from income tax refunds net of income taxes paid	$ 1,759
Convertible Notes exchanged for common stock		$ 98,086	$ 328,017

Consolidated Statements of Changes in Stockholder's Equity - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]
Beginning balance at Dec. 31, 2020	$ 204,557	$ (149,734)	$ 8	$ 1,131,013	$ (165,747)	$ (117)	$ (926,347)	$ 16,013
Beginning balance, Shares at Dec. 31, 2020			76,130
Accounting Standards Update description	ASU 2020-06
Issuance of common stock in follow-on offering, net of offering costs	$ 380,362		$ 1	380,361
Issuance of common stock in follow-on offering, shares			10,063
Issuance of common stock upon exercise of stock options	14,691			14,691
Issuance of common stock upon exercise of stock options, shares			1,063
Issuance of shares in exchange of Convertible Notes, including issuance cost	421,093		$ 1	421,092
Issuance of shares in exchange of Convertible Notes, including issuance cost, shares			10,065
Forfeiture of accrued interest in exchange of Convertible Notes	4,171			4,171
Vesting of restricted stock units, net of shares withheld for taxes	(1,788)			(1,788)
Vesting of restricted stock units, net of shares withheld for taxes. shares			91
Share-based compensation expense	70,667			70,667
Issuance of common stock to employee stock purchase plan	2,970			2,970
Issuance of common stock to employee stock purchase plan, shares			112
Unrealized gain (loss) on available-for-sale investments	9					9
Net loss	(746,354)						(746,354)
Foreign currency loss	(1,982)					(1,982)
Ending balance at Dec. 31, 2021	198,662		$ 10	1,857,430		(2,090)	(1,656,688)
Ending balance, Shares at Dec. 31, 2021			97,524
Issuance of common stock in follow-on offering, net of offering costs	380,120		$ 1	380,119
Issuance of common stock in follow-on offering, shares			8,564
Issuance of common stock upon exercise of stock options	21,483			21,483
Issuance of common stock upon exercise of stock options, shares			1,223
Issuance of shares in exchange of Convertible Notes, including issuance cost	129,636			129,636
Issuance of shares in exchange of Convertible Notes, including issuance cost, shares			3,073
Forfeiture of accrued interest in exchange of Convertible Notes	1,287			1,287
Vesting of restricted stock units, net of shares withheld for taxes	(5,682)			(5,682)
Vesting of restricted stock units, net of shares withheld for taxes. shares			252
Share-based compensation expense	91,085			91,085
Issuance of common stock to employee stock purchase plan	4,238			4,238
Issuance of common stock to employee stock purchase plan, shares			136
Unrealized gain (loss) on available-for-sale investments	(1)					(1)
Unrealized gain (loss) on pension benefit plan	1,646					1,646
Net loss	(652,172)						(652,172)
Foreign currency loss	(430)					(430)
Ending balance at Dec. 31, 2022	169,872		$ 11	2,479,596		(875)	(2,308,860)
Ending balance, Shares at Dec. 31, 2022			110,772
Issuance of common stock and pre-funded warrants in common stock offering	384,387		$ 1	384,386
Issuance of common stock and pre-funded warrants in common stock offering, shares			4,008
Issuance of common stock upon exercise of stock options	$ 71,274			71,274
Issuance of common stock upon exercise of stock options, shares	3,950		3,858
Vesting of restricted stock units, net of shares withheld for taxes	$ (11,040)			(11,040)
Vesting of restricted stock units, net of shares withheld for taxes. shares			806
Share-based compensation expense	105,945			105,945
Issuance of common stock to employee stock purchase plan	5,378			5,378
Issuance of common stock to employee stock purchase plan, shares			112
Unrealized gain (loss) on pension benefit plan	(2,618)					(2,618)
Net loss	(528,628)						(528,628)
Foreign currency loss	(49)					(49)
Ending balance at Dec. 31, 2023	$ 194,521		$ 12	$ 3,035,539		$ (3,542)	$ (2,837,488)
Ending balance, Shares at Dec. 31, 2023			119,556

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued research and development	$ 28,318	$ 34,849
Accrued royalties	10,197	907
Accrued payroll liabilities	51,781	43,212
Product revenue reserves	16,625	2,351
Other	20,885	13,820
Total accrued expenses	$ 127,806	$ 95,139

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, issued	0	0
Preferred stock, outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, issued	119,556,000	110,772,000
Common stock, outstanding	119,556,000	110,772,000

Prepaid and Other Current Assets

12 Months Ended

Dec. 31, 2023

Prepaid Expense and Other Assets, Current [Abstract]

Prepaid and Other Current Assets

5. Prepaid and Other Current Assets

Prepaid assets and other current assets consisted of the following as of December 31, 2023, and December 31, 2022 (in thousands):


	December 31,
	2023		2022
Down payments for inventory	$	16,296	$	13,987
Prepaid research and development		13,931		15,181
Other prepaid expenses		8,593		7,182
Total prepaid expenses	$	38,820	$	36,350


	December 31,
	2023		2022
Royalties receivable		3,054	$	1,442
ERC credit		—		8,711
Receivable from collaboration agreement (1)		15,000		20,000
Deposits and other current assets		4,354		6,505
Total other current assets	$	22,408	$	36,658

(1)

In January 2024 the Company waived the remaining reimbursement payment of $15.0 million in connection with the decision to discontinue the CAD program.

Under the provisions of the Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”) signed into law on March 27, 2020 and the subsequent extension of the CARES Act, the Company was eligible for a refundable employee retention credit (“ERC”) subject to certain criteria. The ERC provides eligible employers with less than 500 employees a refundable tax credit against the employer’s share of social security taxes. The ERC is equal to 70% of qualified wages paid to employees during 2021 calendar year for a maximum credit of $7,000 per employee for each calendar quarter through September 30, 2021. In November 2022, the Company filed for an $8.7 million refund under the CARES Act relating to the ERC. The full refund amount was received in 2023.

Employee Retirement Plans

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Employee Retirement Plans

13. Employee Retirement Plans

In July 2010, the Company adopted an employee profit-sharing plan (the “401(k) Plan”), qualified under Section 401(k) of the Internal Revenue Code (the “IRC”). All of the Company’s full-time employees who have attained the age of 21 are eligible to participate in the 401(k) Plan immediately upon employment. Pursuant to the 401(k) Plan, employees may elect to reduce their current compensation by up to the statutorily prescribed annual limit and have the amount of the reduction contributed to the 401(k) Plan. In 2023, 2022 and 2021, the Company recorded $5.7 million, $4.3 million, and $3.1 million respectively, for employer contributions made to the 401(k) Plan.

The Company maintains a pension plan covering employees of its Swiss subsidiary, Apellis International GmbH (f/k/a Apellis Switzerland GmbH) (the “Swiss Plan”). The Swiss Plan is a government-mandated retirement fund that provides employees with a minimum benefit. Employer and employee contributions are made to the Swiss Plan based on various percentages of salary and wages that vary according to employee age and other factors. As is customary with Swiss pension plans, the assets of the Swiss Plan are invested in a collective fund, which are held and invested by a Swiss insurance company. The investment strategy of the Swiss Plan is managed by an independent asset manager with the objective of achieving a consistent long-term return which will provide sufficient funding for future pension obligations while limiting risk.

As of a December 31, 2023, the Swiss Plan had a funded status of $2.2 million, which resulted from fair value of plan assets of $16.2 million and projected benefit obligation of $18.4 million. The accumulated benefit obligation at December 31, 2023 was $2.6 million. The Company’s net periodic benefit cost for the year ended December 31, 2023 was $0.9 million. The contributions to the Swiss Plan for the year ended December 31, 2023 were not material.

As of a December 31, 2022, the Swiss Plan had a funded status of $18.0 thousand, which resulted from fair value of plan assets of $12.9 million and projected benefit obligation of $12.9 million. The accumulated benefit obligation at December 31, 2022 was $1.6

million. The Company’s net periodic benefit cost for the year ended December 31, 2022 was $0.6 million. The contributions to the Swiss Plan for the year ended December 31, 2022 were not material.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480794/715-70-50-1

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480482/715-20-55-17

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (q)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//715/tableOfContent

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (o)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (p)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (r)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (r)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480126/715-20-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 60
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480266/715-60-50-3

+ Details

License and Collaboration Agreements - Additional Information (Detail)			1 Months Ended											12 Months Ended
	Nov. 30, 2020 USD ($)	Oct. 27, 2020 USD ($)	Jan. 31, 2024 USD ($)	Nov. 30, 2023 USD ($)	Oct. 31, 2023 USD ($)	Apr. 30, 2023 USD ($)	Jan. 31, 2023 USD ($)	Jun. 30, 2022 USD ($)	Apr. 30, 2022 USD ($)	Jan. 31, 2022 USD ($)	Aug. 31, 2021 USD ($)	Jun. 30, 2021 Program	Jan. 31, 2021 USD ($)	Dec. 31, 2023 USD ($) License	Dec. 31, 2022 USD ($)	Dec. 31, 2020 USD ($)	Jul. 31, 2021 USD ($)	Oct. 31, 2020 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalties receivable														$ 3,054,000	$ 1,442,000
Accrued expenses														127,806,000	95,139,000
Subsequent Event [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development cost reimbursement received			$ 15,000,000
SYFOVRE [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty expense incurred														8,900,000
Regulatory milestone payments				$ 2,000,000		$ 2,300,000
Regulatory milestone incurred														5,000,000
Regulatory milestone accrued														3,000,000
Empaveli And Aspaveli [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty expense incurred														7,900,000
Accrued expenses														1,500,000
Swedish Orphan Biovitrum AB (Publ) [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development cost reimbursement		$ 80,000,000.0
Non-refundable Upfront Payment		250,000,000.0
Royalty revenue														$ 10,000,000
Collaboration and License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development cost reimbursement																$ 80,000,000
Collaboration and License Agreement [Member] \| License [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment																$ 250,000,000
Collaboration and License Agreement [Member] \| Swedish Orphan Biovitrum AB (Publ) [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment	$ 250,000,000
Milestone payment received for achievement of regulatory development milestone					$ 5,000,000				$ 50,000,000
Development cost reimbursement													$ 80,000,000
Development cost reimbursement received							$ 20,000,000			$ 20,000,000			25,000,000
Royalties entitled to receive after first commercial sale of applicable licensed product period														10 years
Royalty revenue															3,000,000
Royalties received														$ 10,000,000
Contract research and development expense														0	5,000,000
Remaining reimbursement payment			15,000,000
Contract research and development reimbursement commitment		80,000,000
Contract research and development current														15,000,000
Contract research and development receivable															35,000,000
Contract research and development receivable other current assets															20,000,000
Contract research and development receivable other assets															$ 15,000,000
Proceeds from contract research and development							20,000,000
Collaboration and License Agreement [Member] \| Swedish Orphan Biovitrum AB (Publ) [Member] \| Subsequent Event [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Remaining reimbursement payment			$ 15,000,000
Collaboration and License Agreement [Member] \| Swedish Orphan Biovitrum AB (Publ) [Member] \| ASC Topic 808
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment	$ 250,000,000.0
Development cost reimbursement		80,000,000.0
Collaboration and License Agreement [Member] \| Swedish Orphan Biovitrum AB (Publ) [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate milestone payments upon achievement of specified one time regulatory development and commercial milestone events																		$ 915,000,000
Collaboration and License Agreement [Member] \| Swedish Orphan Biovitrum AB (Publ) [Member] \| Maximum [Member] \| ASC Topic 808
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate milestone payments upon achievement of specified one-time regulatory and commercial milestone events		$ 915,000,000.0
University of Pennsylvania [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Annual maintenance fees														100,000
Development milestone achievement								$ 5,000,000			$ 1,000,000.0
University of Pennsylvania [Member] \| Empaveli And Aspaveli [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments based on annual sales milestones							$ 1,000,000
University of Pennsylvania [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate milestones payments														3,200,000
Milestone payments based on annual sales milestones														5,000,000.0
2010 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Annual maintenance fees														$ 100,000
Number of licensed products \| License														2
2010 License Agreement [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate milestones payments														$ 1,700,000
Milestone payments based on annual sales milestones														2,500,000
Sobi Agreement and Another Licensing Transaction [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sublicense fee owed													$ 25,000,000.0	$ 500,000
Research Collaboration Agreement [Member] \| Beam [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement term												5 years
Number of research programs \| Program												6
Up-front non-refundable payment																	$ 50,000,000
Up-front payment on first anniversary of agreement on June 30, 2022								$ 25,000,000
Collaboration agreement maximum extendable term								2 years

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Dec. 31, 2023	Feb. 20, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Trading Symbol	APLS
Entity Registrant Name	APELLIS PHARMACEUTICALS, INC.
Entity Central Index Key	0001492422
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		120,581,749
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Public Float			$ 10.7
Entity Current Reporting Status	Yes
Entity File Number	001-38276
Entity Tax Identification Number	27-1537290
Entity Address, Address Line One	100 Fifth Avenue
Entity Address, City or Town	Waltham
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02451
City Area Code	617
Local Phone Number	977-5700
Entity Interactive Data Current	Yes
Security 12b Title	Common Stock, $0.0001 par value per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Document Financial Statement Error Correction	false
ICFR Auditor Attestation Flag	true
Auditor Name	Deloitte & Touche LLP
Auditor Firm ID	34
Auditor Location	Boston, Massachusetts
Documents Incorporated by Reference	The registrant intends to file a definitive proxy statement pursuant to Regulation 14A in connection with its 2024 Annual Meeting of Stockholders within 120 days of the end of the registrant’s fiscal year ended December 31, 2023. Portions of such proxy statement are incorporated by reference into Part III of this Annual Report on Form 10-K.

Leases - Maturity of Operating Lease Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
2024	$ 7,393
2025	6,238
2026	5,299
2027	859
Total future minimum lease payments	19,789
Less imputed interest	(1,894)
Total operating lease liabilities	$ 17,895	$ 19,977

Income Taxes - Components of Loss From Continuing Operation Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
United States	$ (48,495)	$ (82,815)	$ (314,673)
Foreign	(478,001)	(568,688)	(431,329)
Net loss before taxes	$ (526,496)	$ (651,503)	$ (746,002)

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(11))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(b)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479557/942-235-S99-1

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-SubTopic 20
-Topic 940
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481913/940-20-25-1

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(10))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(15))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

+ Details

Product Revenues, Accounts Receivable, and Reserves for Product Sales - Summary of Product Revenue Allowance and Reserve Categories (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Chargebacks, Discounts, and Fees [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 164	$ 67
Provision related to sales in the current year	17,690	614
Adjustments related to prior period sales	(112)	(156)
Credits and payments made	(12,068)	(362)
Ending balance	5,674	164
Government and Other Rebates [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	1,936	716
Provision related to sales in the current year	26,661	4,569
Adjustments related to prior period sales	(1,223)	(246)
Credits and payments made	(18,476)	(3,103)
Ending balance	8,898	1,936
Returns [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	251	167
Provision related to sales in the current year	4,698	1,185
Adjustments related to prior period sales	(2,481)	(385)
Credits and payments made	(415)	(716)
Ending balance	2,053	251
Product Revenue Allowance and Reserves [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	2,351	951
Provision related to sales in the current year	49,050	6,368
Adjustments related to prior period sales	(3,817)	(787)
Credits and payments made	(30,960)	(4,181)
Ending balance	$ 16,625	$ 2,351

Equity Incentive Plans - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares Outstanding, Beginning balance	12,295
Shares, Granted	838	1,300	2,700
Shares, Exercised	(3,950)
Shares, Forfeited	(519)
Shares Outstanding, Ending balance	8,664	12,295
Shares, Options exercisable	6,712
Shares, Expected to vest	1,952
Weighted -Average Exercise Price Per Share Outstanding, Beginning balance	$ 26.31
Weighted -Average Exercise Price Per Share, Granted	52.48
Weighted -Average Exercise Price Per Share, Exercised	20.11
Weighted -Average Exercise Price Per Share, Forfeited	43.65
Weighted -Average Exercise Price Per Share, Outstanding, Ending balance	30.65	$ 26.31
Weighted -Average Exercise Price Per Share, Options exercisable	26.2
Weighted -Average Exercise Price Per Share, Expected to vest	$ 45.97
Weighted - Average Contractual Life Outstanding, Balance		6 years 2 months 26 days
Weighted - Average Contractual Life, Options exercisable	5 years 4 months 20 days
Weighted - Average Contractual Life, Expected to vest	8 years 1 month 17 days
Aggregate Intrinsic Value, Outstanding		$ 317,031
Aggregate Intrinsic Value, Options exercisable	$ 226,419
Aggregate Intrinsic Value, Expected to vest	$ 27,515

Development Liability (Tables)

12 Months Ended

Dec. 31, 2023

Research and Development [Abstract]

Summary of Development Liability

The following table summarizes the development liability (in thousands):


	December 31,
	2023			2022			Effective Interest Rate
Development liability	$	366,000		$	421,500			7.91	%
Less: Unamortized discount to development liability		(50,353	)		(76,349	)
Less: Current portion of development liability, net of discount		(75,830	)		(29,504	)
Total long term development liability		239,817			315,647

Schedule of Future Minimum SFJ Payments

Future minimum SFJ payments as of December 31, 2023 is as follows (in thousands):

Nature of Organization and Operations - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Feb. 22, 2023	Mar. 28, 2022	Nov. 18, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Nature Of Organization And Operations [Line Items]
Proceeds from follow-on public offering after deducting underwriting discounts and commissions					$ 380,120	$ 380,363
Accumulated deficit				$ (2,837,488)	(2,308,860)
Cash and cash equivalents				$ 351,185	$ 551,801	$ 640,192
Follow-on Public Offerings [Member]
Nature Of Organization And Operations [Line Items]
Issuance of common stock and pre-funded warrants in common stock offering, shares	4,007,936
Pre funded warrant price	$ 62.9999
Common stock pre funded warrants per warrant	0.0001
Issuance of common stock in follow-on offering, shares		8,563,830	10,062,500
Price of common stock	$ 63	$ 47	$ 40.00
Proceeds from follow-on public offering after deducting underwriting discounts and commissions	$ 384,400	$ 380,100	$ 380,400
Underwriting discounts and commissions	18,800	22,100	22,100
Offering Costs	$ 300	$ 300	$ 600
Over Allotment Option [Member]
Nature Of Organization And Operations [Line Items]
Issuance of common stock in follow-on offering, shares		1,117,021	1,312,500
Price of common stock		$ 47	$ 40.00
Common Stock [Member]
Nature Of Organization And Operations [Line Items]
Issuance of common stock and pre-funded warrants in common stock offering, shares				4,008,000
Issuance of common stock in follow-on offering, shares					8,564,000	10,063,000
Common Stock [Member] \| Follow-on Public Offerings [Member]
Nature Of Organization And Operations [Line Items]
Issuance of common stock and pre-funded warrants in common stock offering, shares	2,380,956
Common Stock [Member] \| Over Allotment Option [Member]
Nature Of Organization And Operations [Line Items]
Issuance of common stock and pre-funded warrants in common stock offering, shares	833,333

Inventory - Schedule Of Inventory Current (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Inventory Disclosure [Abstract]
Raw materials	$ 32,724	$ 29,847
Semi-finished goods	82,924	54,101
Finished goods	30,714	1,766
Total inventories	$ 146,362	$ 85,714

Other Comprehensive Income and Accumulated Other Comprehensive Income (Tables)

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Summary of Changes in Accumulated Other Comprehensive Income/(Loss), by Component

The following tables summarize the changes in accumulated other comprehensive income/(loss), by component for the years ended December 31, 2023 and 2022 (in thousands):


	Unrealized Gains (Losses) from Marketable Securities			Foreign Currency Translation Adjustment			Unrealized Gains (Losses) from Pension Plan			Total Accumulated Other Comprehensive Income (Loss)
Balances, December 31, 2022	$	—		$	(2,521	)	$	1,646		$	(875	)
Net other comprehensive income (loss)		—			(49	)		(2,618	)	$	(2,667	)
Balances, December 31, 2023	$	—		$	(2,570	)	$	(972	)	$	(3,542	)


	Unrealized Gains (Losses) from Marketable Securities			Foreign Currency Translation Adjustment			Unrealized Gains (Losses) from Pension Plan			Total Accumulated Other Comprehensive Income (Loss)
Balances, December 31, 2021	$	1		$	(2,091	)	$	—		$	(2,090	)
Net other comprehensive income (loss)		(1	)		(430	)		1,646		$	1,215
Balances, December 31, 2022	$	—		$	(2,521	)	$	1,646		$	(875	)

Prepaid and Other Current Assets - Summary of Prepaid Assets and Other Current Assets (Details) - USD ($)
$ in Thousands

Dec. 31, 2023

Dec. 31, 2022

Prepaid Expense and Other Assets, Current [Abstract]

Down payments for inventory

$ 16,296

$ 13,987

Prepaid research and development

13,931

15,181

Other prepaid expenses

8,593

7,182

Total prepaid expenses

38,820

36,350

Royalties receivable

3,054

1,442

ERC credit

8,711

Receivable from collaboration agreement

^[1]

15,000

20,000

Deposits and Other Current Assets

4,354

6,505

Total other current assets

$ 22,408

$ 36,658

[1]	In January 2024 the Company waived the remaining reimbursement payment of $15.0 million in connection with the decision to discontinue the CAD program.

Leases - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Lessee Lease Description [Line Items]
Operating lease description	The Company enters into lease agreements with terms generally ranging from 2-7 years. Some of the Company’s lease agreements include Company options to extend the lease on a month-to-month basis or for set periods for up to five years. Many leases also include options to terminate the leases within one year or per other contractual terms. Renewal and termination options were generally not included in the lease term for the Company’s existing operating leases.
Operating lease, existence of option to extend	true
Operating lease maximum term of options to terminate lease	1 year
Operating lease expense	$ 7.0	$ 6.2	$ 5.6
Minimum [Member]
Lessee Lease Description [Line Items]
Operating lease, term of contract	2 years
Maximum [Member]
Lessee Lease Description [Line Items]
Operating lease, term of contract	7 years
Operating lease options to extend lease	5 years

Leases

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Leases

9. Leases

The underlying assets of the Company’s leases primarily relate to office space leases, but also include some equipment leases. The Company determines if an arrangement qualifies as a lease at its inception.

As a practical expedient permitted under Topic 842, the Company has elected to account for the lease and non-lease components as a single lease component for all leases of which it is the lessee. Lease payments, which may include lease and non-lease components, are included in the measurement of the Company’s lease liabilities to the extent that such payments are either fixed amounts or variable amounts that depend on a rate or index as stipulated in the lease contract. When the Company cannot readily determine the rate implicit in the lease, the Company determines its incremental borrowing rate by using the rate of interest that it would have to pay to borrow on a collateralized basis over a similar term, an amount equal to the lease payments in a similar economic environment.

The Company enters into lease agreements with terms generally ranging from 2-7 years. Some of the Company’s lease agreements include Company options to extend the lease on a month-to-month basis or for set periods for up to five years. Many leases also include options to terminate the leases within one year or per other contractual terms. Renewal and termination options were generally not included in the lease term for the Company’s existing operating leases.

As of December 31, 2023 and 2022, all leases were classified as operating lease assets and liabilities. Additional information related to the operating lease assets and liabilities is as follows (in thousands):


	December 31,			December 31,
	2023			2022
Operating lease assets	$	16,745		$	18,747
Operating lease liabilities	$	17,895		$	19,977
Weighted average remaining term in years		2.83			3.57
Weighted average discount rate used to measure outstanding lease liabilities		7.20	%		7.26	%

For the years ended December 31, 2023, 2022, and 2021, the total lease cost for operating lease expense was approximately $7.0 million, $6.2 million, and $5.6 million, respectively.

Supplemental cash flow information related to operating leases for the years ended December 31, 2023, 2022 and 2021 is as follows (in thousands):


	2023		2022		2021
Operating cash flows from operating leases	$	7,939	$	7,375	$	5,989
Operating lease assets obtained in exchange for lease obligations		2,700		—	$	5,675

The maturity of the Company’s operating lease liabilities as of December 31, 2023 are as follows (in thousands):


2024	$	7,393
2025		6,238
2026		5,299
2027		859
Total future minimum lease payments		19,789
Less imputed interest		(1,894	)
Total operating lease liabilities	$	17,895

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following as of December 31, 2023, and December 31, 2022 (in thousands):


	December 31,
	2023		2022
Accrued research and development	$	28,318	$	34,849
Accrued royalties		10,197		907
Accrued payroll liabilities		51,781		43,212
Product revenue reserves		16,625		2,351
Other		20,885		13,820
Total accrued expenses	$	127,806	$	95,139

Long-term Debt - Schedule of Outstanding Balance of Convertible Notes (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Principal	$ 102,797
Less: debit discount and issuance costs, net	(864)
Net carrying amount	93,033
Convertible Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Principal	93,897	$ 93,897
Less: debit discount and issuance costs, net	864	(1,161)
Net carrying amount	$ 93,033	$ 92,736

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482900/835-30-50-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
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-Paragraph 1
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-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/exampleRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1F

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1F

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1F

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

+ Details

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References + Details

Equity Incentive Plans - Schedule of Unvested Restricted Stock Units Activity (Detail) - Restricted Stock Units [Member] shares in Thousands	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Number of Stock Units
Unvested Beginning Balance \| shares	3,572
Granted \| shares	2,916
Vested \| shares	(1,015)
Forfeited \| shares	(1,172)
Unvested Ending Balance \| shares	4,301
Weighted Average Grant Date Fair Value Per Share
Unvested Balance at December 31, 2022 \| $ / shares	$ 42.23
Granted \| $ / shares	52.19
Vested \| $ / shares	41.52
Forfeited \| $ / shares	48.43
Unvested Balance at December 31, 2023 \| $ / shares	$ 47.48

Development Liability

12 Months Ended

Dec. 31, 2023

Research and Development [Abstract]

Development Liability

6. Development Liability

On February 28, 2019, the Company entered into a development funding agreement with SFJ (the “SFJ agreement”), under which SFJ agreed to provide funding to the Company to support the development of pegcetacoplan for the treatment of patients with PNH. Pursuant to the agreement, SFJ paid the Company $60.0 million following the signing of the agreement and agreed to pay the Company up to an additional $60.0 million in the aggregate in three equal installments upon the achievement of specified development milestones with respect to the Company’s Phase 3 program for pegcetacoplan in PNH and subject to the Company having cash resources at the time sufficient to fund at least 10 months of the Company’s operations.

In June 2019 we amended the SFJ agreement to include an additional $20 million funding payment. SFJ paid us $80.0 million under the amended SFJ agreement between June 2019 and January 2020.

Under the SFJ agreement, following regulatory approval by the FDA in May 2021 for the use of systemic pegcetacoplan as a treatment for PNH, the Company became obligated to pay SFJ an initial payment of $4.0 million and then an additional $226.0 million in the aggregate in six additional annual payments with the majority of the payments being made from the third anniversary to the sixth anniversary of regulatory approval. The Company paid SFJ the initial payment of $4.0 million in June 2021, its first annual payment of $11.5 million in May 2022 and its second annual payment of $24.5 million in May 2023. The subsequent annual payments remaining are due and payable in May of each year from 2024 through 2027.

Following regulatory approval of systemic pegcetacoplan by the European Medicines Agency(“EMA”) in December 2021, the Company became obligated to pay SFJ an initial payment of $5.0 million and then an additional $225.0 million in the aggregate in six additional annual payments with the majority of the payments being made from the third anniversary to the sixth anniversary of regulatory approval. The Company paid SFJ the initial payment of $5.0 million in January 2022 its first annual payment of $18.0 million in December 2022 and its second annual payment of $31.0 million in December 2023. The subsequent annual payments are due and payable in December of each year from 2024 through 2027.

The Company has paid SFJ a total of $94.0 million as of December 31, 2023.

Additionally, the Company granted a security interest to SFJ in all of its assets, excluding intellectual property and license agreements to which it is a party. In connection with the grant of the security interest, the Company agreed to certain affirmative and negative covenants, including restrictions on its ability to pay dividends, incur additional debt or enter into licensing transactions with respect to its intellectual property, other than specified types of licenses.

From December 15, 2021 to the final annual payment due in December 2027, the development liability will be accreted from its initial carrying amount to the total payment amount using the effective interest rate method under the ASC Topic 835, Interest, over the remaining life of the SFJ agreement. The difference between the carrying amount and the total payment amount is presented as a discount to the development liability. The accretion is recorded as interest expense in the unaudited condensed consolidated statement of operations.

The following table summarizes the development liability (in thousands):


	December 31,
	2023			2022			Effective Interest Rate
Development liability	$	366,000		$	421,500			7.91	%
Less: Unamortized discount to development liability		(50,353	)		(76,349	)
Less: Current portion of development liability, net of discount		(75,830	)		(29,504	)
Total long term development liability		239,817			315,647

As of December 31, 2023 and December 31, 2022 interest expense of $26.0 million and $26.9 million was recorded for the accretion of the development liability. For the period from December 15, 2021 through December 31, 2021, $1.2 million of interest expense was recorded for the accretion of the development liability.

Future minimum SFJ payments as of December 31, 2023 is as follows (in thousands):

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Intangible assets	$ 192,444	$ 187,839
Share-based compensation	31,712	29,673
Net operating loss carryforwards	329,135	228,985
Research and development credits	67,667	57,419
Orphan drug credits	34,023	30,160
Development derivative liability	75,190	79,374
Convertible debt	5,582	6,850
Fixed Assets	18
Lease liability	2,888	4,304
Accruals	17,401	16,272
Total deferred tax assets	756,060	640,876
Deferred tax liabilities:
Fixed assets		(91)
Right-of-use asset	(2,672)	(4,032)
481(a) adjustment		(233)
Total deferred tax liabilities	(2,672)	(4,356)
Net deferred tax assets before allowance:	753,388	636,520
Less valuation allowance	$ (753,388)	$ (636,520)

Net Loss per Common Share

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Net Loss per Common Share

17. Net Loss per Common Share

The following table presents the calculation of basic and diluted net loss per common share (amounts in thousands except per share amounts):


	Year Ended December 31,
	2023			2022			2021
Numerator:
Net loss	$	(528,628	)	$	(652,172	)	$	(746,354	)
Denominator:
Weighted-average number of common shares used in net loss per common share - basic and diluted		118,678			106,114			84,421
Net loss per common share -- basic and diluted	$	(4.45	)	$	(6.15	)	$	(8.84	)

Shares outstanding presented below were excluded from the calculation of diluted net loss per share, prior to the use of the if-converted-method and treasury stock method, as their effect is anti-dilutive (in thousands):


	Year Ended December 31,
	2023		2022		2021
Convertible notes		2,379		2,379		4,865
Common stock under option		8,664		12,295		12,562
Restricted stock units		4,301		3,572		1,224
Total		15,344		18,246		18,651

Long-term Debt - Schedule of Future Minimum Payments on Convertible Notes Payable (Detail) $ in Thousands	Dec. 31, 2023 USD ($)
Debt Disclosure [Abstract]
2024	$ 3,286
2025	3,286
2026	96,225
Total future minimum payments	102,797
Less: interest	(8,900)
Less: debit discount and issuance costs, net	(864)
Net carrying amount	$ 93,033

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References + Details

Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Summary of Shares of Common Stock Reserved for Future Issuance

The Company has reserved the following shares of common stock for future issuance (in thousands):


	December 31,
	2023		2022		2021
Shares reserved under 2017 Equity Incentive Plan		16,989		14,271		11,014
Shares reserved under 2017 Employee Stock Purchase Plan		553		665		801
Shares reserved under 2020 Inducement Stock Incentive Plan		1,638		1,857		1,761
Total		19,180		16,793		13,576

Summary of Share-based Compensation Expense

Total share-based compensation expense related to the various plans during the years ended was as follows (in thousands):


	Year Ended December 31,
	2023		2022		2021
Research and development	$	45,644	$	42,052	$	30,586
General and administrative		60,301		49,033		40,081
Total share-based compensation expense	$	105,945	$	91,085	$	70,667

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity:


				Weighted -		Weighted -
				Average		Average		Aggregate
				Exercise		Contractual		Intrinsic
	Shares			Price		Life		Value
	(in thousands)			Per Share		(in years)		(in thousands)
Outstanding, December 31, 2022		12,295		$	26.31		6.24		317,031
Granted		838			52.48
Exercised		(3,950	)		20.11
Forfeited		(519	)		43.65
Outstanding, December 31, 2023		8,664		$	30.65
Options exercisable, December 31, 2023		6,712		$	26.20		5.39	$	226,419
Expected to vest, December 31, 2023		1,952		$	45.97		8.13	$	27,515

Summary of Assumption Used to Estimate the Grant Date Fair Value

The assumptions used in the Black-Scholes model to estimate the grant date fair value are as follows:


	Year Ended December 31,
	2023	2022	2021
Risk-free interest rate	3.50 - 4.01%	1.15 - 3.37%	0.41 - 1.34%
Dividend yield	0%	0%	0%
Volatility	68.4 - 71.0%	68.3 - 70.4%	71.7 - 74.4%
Expected terms (years)	3.81 - 6.08	3.81 - 6.08	5.31 - 6.08

Schedule of Unvested Restricted Stock Units Activity

The following table summarizes the Company’s RSU's activity:


	Number of Stock Units (in thousands)			Weighted Average Grant Date Fair Value Per Share
Unvested Balance at December 31, 2022		3,572		$	42.23
Granted		2,916			52.19
Vested		(1,015	)		41.52
Forfeited		(1,172	)		48.43
Unvested Balance at December 31, 2023		4,301			47.48

Product Revenues, Accounts Receivable, and Reserves for Product Sales - Schedule of Customer Accounted for 10% of More of Gross Product Revenues and Accounts Receivable (Detail) - Customer Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Gross Product Revenues [Member] \| Customer A [Member]
Revenue, Major Customer [Line Items]
Concentration risk	24.00%	99.00%	99.00%
Gross Product Revenues [Member] \| Customer C [Member]
Revenue, Major Customer [Line Items]
Concentration risk	16.00%
Gross Product Revenues [Member] \| Customer D [Member]
Revenue, Major Customer [Line Items]
Concentration risk	54.00%	1.00%
Accounts Receivable [Member] \| Customer A [Member]
Revenue, Major Customer [Line Items]
Concentration risk	4.00%	96.00%
Accounts Receivable [Member] \| Customer C [Member]
Revenue, Major Customer [Line Items]
Concentration risk	66.00%
Accounts Receivable [Member] \| Customer D [Member]
Revenue, Major Customer [Line Items]
Concentration risk	22.00%	3.00%

Net Loss per Common Share (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Summary of Basic and Diluted Net Loss per Common Share

The following table presents the calculation of basic and diluted net loss per common share (amounts in thousands except per share amounts):


	Year Ended December 31,
	2023			2022			2021
Numerator:
Net loss	$	(528,628	)	$	(652,172	)	$	(746,354	)
Denominator:
Weighted-average number of common shares used in net loss per common share - basic and diluted		118,678			106,114			84,421
Net loss per common share -- basic and diluted	$	(4.45	)	$	(6.15	)	$	(8.84	)

Summary of Shares Outstanding that were Excluded from Calculation of Diluted Net Loss Per Share


	Year Ended December 31,
	2023		2022		2021
Convertible notes		2,379		2,379		4,865
Common stock under option		8,664		12,295		12,562
Restricted stock units		4,301		3,572		1,224
Total		15,344		18,246		18,651

Commitments and Contingencies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2023 USD ($)
Commitments And Contingencies [Line Items]
Incurred any cost to defend lawsuits or settle claims	$ 0
Vehicles [Member]
Commitments And Contingencies [Line Items]
Operating lease, term of contract	36 months
Bachem Americas, Inc [Member]
Commitments And Contingencies [Line Items]
Non-cancellable purchase obligation substance over period	5 years
Non-cancellable purchase commitments	$ 94,600,000
Other non-cancellable purchase commitments	$ 16,100,000

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Level 1 [Member] \| Convertible Senior Notes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Convertible notes	$ 140.8	$ 143.9
Convertible notes, interest rate	3.50%	3.50%
Level 2 [Member] \| Development Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value	$ 306.9	$ 315.8

Inventory

12 Months Ended

Dec. 31, 2023

Inventory Disclosure [Abstract]

Inventory

4. Inventory

The Company’s inventory of EMPAVELI and SYFOVRE consisted of the following as of December 31, 2023, and December 31, 2022 (in thousands):


	December 31,
	2023		2022
Raw materials	$	32,724	$	29,847
Semi-finished goods		82,924		54,101
Finished goods		30,714		1,766
Total inventories	$	146,362	$	85,714

License and Collaboration Agreements

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

License and Collaboration Agreements

12. License and Collaboration Agreements

Sobi License and Collaboration Agreement

In October 2020, the Company and its subsidiaries Apellis International GmbH (f/k/a Apellis Switzerland GmbH) and APL DEL Holdings, LLC entered into a Collaboration and License Agreement with Sobi, concerning the development and commercialization of pegcetacoplan and specified other structurally and functionally similar compstatin analogues or derivatives for use systemically or for local non-ophthalmological administration (collectively referred to as the “Licensed Products”).

Under the Sobi collaboration agreement, the Company granted Sobi an exclusive (subject to certain retained rights of the Company), sublicensable license of certain patent rights and know-how to develop and commercialize Licensed Products in all countries outside of the United States.

The Company retains the right to commercialize Licensed Products in the United States, and, subject to specified limitations, to develop Licensed Products worldwide for commercialization in the United States.

Under the Sobi collaboration agreement, the Company and Sobi have agreed to collaborate to develop Licensed Products for the treatment of PNH, CAD, HSCT-TMA, C3G, IC-MPGN and ALS, or collectively the “Initial Indications”, and any other indications subsequently agreed upon by the parties, for commercialization by or on behalf of the Company in the United States and by or on behalf of Sobi outside of the United States. If the parties do not agree to jointly pursue any development activities for the Licensed Products (whether for an Initial Indication or otherwise), the party proposing to pursue such activities may conduct such activities at its sole expense (with the non-proposing party having the right to obtain rights to the data generated by such development activities by paying a specified percentage of that expense), subject to agreed-upon exceptions that limit each party’s unilateral development rights.

The initial development plan sets forth the initial development activities to be conducted by each of the Company and Sobi, with the Company bearing all costs incurred in conducting the activities set forth in such initial development plan, as well as certain specified additional costs that are not included in the initial development plan that may be incurred by the parties in developing Licensed Products for PNH in the European Union and the United Kingdom. The Company and Sobi have formed several governance committees to oversee the development and manufacture, and to review and discuss the commercialization, of Licensed Products. The Company and SOBI have discontinued to development programs in ALS and CAD.

The Company shall supply Licensed Products to Sobi for development and for commercialization outside of the United States in accordance with a supply agreement to be negotiated by the parties. The collaboration agreement grants Sobi the right to perform or have performed drug product manufacturing of Licensed Products for development and for commercialization outside the United States and to manufacture or have manufactured drug substance under certain circumstances.

Sobi paid the Company an upfront payment of $250.0 million in November 2020 and has agreed to pay up to an aggregate of $915.0 million upon the achievement of specified one-time regulatory and commercial milestone events, of which the Company received $50.0 million in April 2022 for the achievement of a regulatory development milestone in Europe and $5.0 million in October 2023 for the achievement of a regulatory development milestone in Japan. Sobi also agreed to reimburse the Company for up to $80.0 million in development costs, of which the Company received $25.0 million in January 2021, $20.0 million in January 2022 and $20.0 million in January 2023. In January 2024, the Company waived the remaining reimbursement payment of $15.0 million in connection with the to discontinue the CAD program. The Company is also entitled to receive tiered, double-digit royalties (ranging from high teens to high twenties) on sales of Licensed Products outside of the United States, subject to customary deductions and third-party payment obligations, until the latest to occur of: (i) expiration of the last-to-expire of specified licensed patent rights; (ii) expiration of regulatory exclusivity; and (iii) ten (10) years after the first commercial sale of the applicable Licensed Product, in each case on a Licensed Product-by-Licensed Product and country-by-country basis. The Company received $10.0 million in royalties from Sobi during 2023. Under the Sobi collaboration agreement, the Company remains responsible for its license fee obligations (including royalty obligations) to the Trustees of the University of Pennsylvania (“Penn”), as a licensor of the Company and for its payment obligations to SFJ.

Sobi Accounting Analysis

The Company has determined that the agreement is within the scope of ASC 808 as a contractual arrangement that involves a joint operating activity whereby both parties are (i) active participants in the activity and (ii) exposed to certain significant risks and rewards dependent on the commercial success of the activity. ASC Topic 808 does not address measurement or recognition matters but allows for analogizing to ASC 606. Pursuant to ASC 606, the Company performed the following five steps: (i) identified the contract(s) with a customer; (ii) identified the performance obligations in the contract; (iii) determined the transaction price; (iv) allocated the transaction price to the performance obligations in the contract; and (v) recognized revenue when (or as) the entity satisfies a performance obligation.

The Company identified the following material distinct promises under the Sobi Agreement: (1) licenses to develop and commercialize pegcetacoplan or, Licenses to IP, and (2) performance of research and development services. The Company determined the promises to be distinct because Sobi can benefit from each of the license and the development services on their own or with readily available services. The Company could have provided the license without any development services and Sobi would have been able to benefit from it by obtaining development services from another provider as the Licensed Products are at a more mature stage in their life cycle.

Under the agreement, Sobi agreed to pay the Company

a fixed amount of $250.0 million in an upfront payment in November 2020;

ii)

a fixed amount of an additional $80.0 million in development reimbursements, payable yearly in four tranches in amounts determined based upon actual expenses incurred by the Company;

iii)

up to an aggregate of $915.0 million upon the achievement of specified one-time regulatory and commercial milestone events; and

iv)

tiered, double-digit royalties, ranging from high teens to high twenties, on sales of Licensed Products outside of the United States, subject to customary deductions and third-party payment obligations.

At contract inception, the $250.0 million non-refundable payment and the $80.0 million reimbursements were fixed proceeds. The Company evaluated whether Sobi is a customer for either of the distinct promises in the agreement. Under the Licenses to IP, the Company determined that Sobi is a customer as the know-how provided and the right granted by the Company to Sobi are outputs of the Company’s business activities for which the Company will receive consideration. With respect to research and development activity, management determined that there is no vendor relationship as performing research and development activities for others is not a part of the Company’s ongoing central operations. Based upon the evaluation of the relative fair values, the Company allocated the purchase price of $250.0 million and the related milestones and royalties to the license of IP and $80.0 million to performance of research and development activities.

The milestone and royalty payments are subject to activities outside the control of the Company. Per ASC 606, the Company considers this to be a customer/ vendor relationship, therefore, the Company will include the regulatory milestone payments in the total transaction price when it is probable that a significant reversal of revenue would not occur in a future period. The Company will recognize commercial milestone and royalty revenue at the later of (i) when the related sales occur or (ii) when the performance obligation to which the commercial milestone or royalty has been allocated has been satisfied. In case of commercial milestone or royalty payments, the Company will recognize revenue in the same period that the sales are completed for which the Company is contractually entitled to the milestone or percentage-based royalty payment. Management will periodically assess the elements of the contract and re-evaluate revenue recognition as necessary.

Pursuant to ASC 606, during the year ended December 31, 2020, the Company has recognized the $250.0 million in revenue as this is the amount allocated to the license. The $80.0 million reimbursement for research and development activities does not constitute a customer/vendor relationship and thus is not in the scope of ASC 606. As ASC 808 does not include recognition guidance, the Company has established an accounting policy to recognize the payments under the reimbursement as a receivable on the balance sheet in an amount that is to be reimbursed based upon expense incurred by the Company, with a contra- research and development expense recognized in the statement of operations, over time as the expenses are incurred.

Under the Sobi collaboration agreement, for the year ended December 31, 2023, the Company recognized $10.0 million of royalty revenue. For the year ended December 31, 2022, the Company recognized $3.0 million of royalty revenue. For the year ended December 31, 2023, the Company did not recognize any contra-research and development expense in the consolidated statement of operations related to the $80.0 million reimbursement commitment from Sobi. For the year ended December 31, 2022, the Company recognized $5.0 million for contra-research and development expense in the consolidated statement of operations related to the $80.0 million reimbursement commitment from Sobi.

As of December 31, 2023, the Company recorded $15.0 million in current assets, which represents the receivable for contra-research and development expenses incurred but not yet reimbursed from Sobi. The total receivable balance as of December 31, 2023 was for contra-research and development expenses incurred but not yet reimbursed from Sobi. In January 2024, the Company waived the remaining reimbursement payment of $15.0 million in connection with the decision to discontinue the CAD program.

As of December 31, 2022, the Company recorded a receivable of $35.0 million, with $20.0 million in other current assets and $15.0 million in other assets on the consolidated balance sheet. The total receivable balance as of December 31, 2022 is for contra-research and development expenses incurred but not yet reimbursed from Sobi. The Company received the $20.0 million recorded in other current assets in January 2023.

University of Pennsylvania License Agreement

The Company is a party to a license agreement with the Trustees of the University of Pennsylvania (“Penn”) for an exclusive, worldwide license to specified patent rights. The Company is required to pay annual maintenance fees of $0.1 million until the first sale of a licensed product. The Company is also required to make milestone payments aggregating up to $3.2 million based upon the achievement of specified development and regulatory milestones and up to $5.0 million based upon the achievement of specified annual sales milestones with respect to each licensed product, and to pay low single-digit royalties based on net sales of each licensed product and with minimum quarterly royalty thresholds. In addition, the Company is obligated to pay a specified portion of income it receives from sublicensees.

In April 2023, the Company paid $2.3 million for the achievement of a regulatory milestone as a result of the FDA approval of SYFOVRE in February 2023. In 2023 the Company incurred $5.0 million as a result of the achievement of sales milestones for SYFOVRE of which $2.0 million the Company paid in October 2023 and remaining of $3.0 million is accrued for as of December 31, 2023.

As of December 31, 2023, the Company has incurred an aggregate royalty expense of $8.9 million on sales of SYFOVRE.

In addition, the Company is also party to a license agreement with Penn for an exclusive, worldwide license to specified patent rights for the development and commercialization of products in fields of use, as defined therein. The Company is required to pay annual maintenance fees of $0.1 million until the first sale of a licensed product. The Company is required to make milestone payments aggregating up to $1.7 million, based upon the achievement of development and regulatory approval milestones, and up to $2.5 million, based upon the achievement of annual sales milestones with respect to each of the first two licensed products. The license agreement also requires the Company to pay low single digit royalties based on net sales of each licensed product, subject to minimum quarterly royalty thresholds. In addition, the Company is obligated to pay a specified portion of income it receives from sublicensees.

In January 2021, the Company paid $25.0 million for sublicense fee owed to Penn related to the Sobi Agreement and another licensing transaction. In August 2021, the Company paid $1.0 million to Penn upon the achievement of a development milestone, net of a credit for the annual license maintenance payment. In June 2022, the Company paid an additional $5.0 million to Penn upon the achievement of a development milestone. In January 2023, the Company paid $1.0 million to Penn upon the achievement of a sales milestone for EMPAVELI in 2022. As December 31, 2023, the Company recorded in accrued expenses $0.5 million for a sublicense fee owed to Penn related to Sobi obtaining regulatory approval in Japan. Additionally, as of December 31, 2023, the Company recorded in accrued expenses $1.5 million as a result of the achievement of a sales milestone for EMPAVELI and Aspaveli.

As of December 31, 2023, the Company has incurred an aggregate royalty expense of $7.9 million on sales of EMPAVELI and Aspaveli.

Beam Research Collaboration

In June 2021, the Company entered into an exclusive five-year research collaboration with Beam Therapeutics, Inc. (“Beam”) focused on the use of Beam’s proprietary base editing technology to discover new treatments for complement-driven diseases. The Company and Beam agreed to collaborate on up to six research programs focused on C3 and other complement targets in the eye, liver and brain. Under the terms of the collaboration agreement, Apellis is responsible for selecting specific genes within the complement system in various organs including the eye, liver and brain (the “Target List”) and providing analytical support while Beam will apply its base editing technology and conduct preclinical research on up to six base editing programs for the Target List. During the first five years of the collaboration agreement, Beam is prohibited from developing on its own or with a third party any base editing therapies associated with the items on the Target List but does not prevent Beam from licensing its intellectual property to a third-party for another purpose outside of the Target List. The Company will have exclusive rights to license each of the six programs and will assume responsibility for subsequent development and commercialization. Beam may elect to enter a 50-50 co-development and U.S. co-commercialization agreement with the Company with respect to any one program licensed under the collaboration and upon such election any license agreement in place at that time, would be terminated.

As part of the Beam collaboration agreement, the Company agreed to pay a $50.0 million up-front, non-refundable payment to Beam, which the Company paid in July 2021. In June 2022, the Company paid $25.0 million, which was recorded as a cost of research collaboration expense for the year ended December 31, 2021, as it was considered probable of achievement. The Company and Beam are each responsible for their own costs during the research collaboration. If and after the opt-in license rights are exercised for each of the up to six programs, Beam will be eligible to receive development, regulatory and sales milestones from the Company, as well as royalty payments on sales. The Beam collaboration agreement has an initial term of five years and may be extended up to two years on a per year program-by-program basis.

The Company analyzed the research collaboration agreement pursuant to ASC 808 to assess whether the agreement involved joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. Since each party is actively participating in this activity and exposed to significant risks and rewards related to the activity through each party’s costs will be accounted for under ASC 808.

Since ASC 808 does not provide recognition guidance, the Company referred to the guidance under ASC 730 to arrangements involving payments by the Company. ASC 730 requires the Company to recognize research and developments costs as expense as incurred since the payment was made for the use of Beam’s intellectual property and research and development services and there is no alternative use.

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

14. Income Taxes

The components of loss from continuing operations before provision for income taxes are as follows (in thousands):


	Year Ended December 31,
	2023			2022			2021
United States	$	(48,495	)	$	(82,815	)	$	(314,673	)
Foreign		(478,001	)		(568,688	)		(431,329	)
Total	$	(526,496	)	$	(651,503	)	$	(746,002	)

Provision for income taxes for the years ended December 31, 2023, 2022, and 2021 are as follows (in thousands):


	Year Ended December 31, 2023		Year Ended December 31, 2022		Year Ended December 31, 2021
Current income tax expense:
U.S. Federal	$	—	$	—	$	—
U.S. State and Local		1,869		520		205
Foreign		263		149		147
Total current income tax expense		2,132		669		352
Deferred income tax expense:
U.S. Federal		—		—		—
U.S. State and Local		—		—		—
Foreign		—		—		—
Total deferred income tax expense		—		—		—
Total tax expense	$	2,132	$	669	$	352

A reconciliation between the U.S. federal statutory tax rate and the Company's effective tax rate is summarized as follows (in thousands):


	Year Ended December
	2023						2022						2021
	Amount			Percentage of income before income taxes			Amount			Percentage of income before income taxes			Amount			Percentage of income before income taxes
Statutory U.S. federal income tax	$	(110,564	)		21.0	%	$	(136,816	)		21.0	%	$	(156,660	)		21.0	%
Foreign tax rate differential		42,100			(8.0	)		50,219			(7.7	)		38,677			(5.2	)
State income taxes, net of federal benefit		(13,438	)		2.6			9,051			(1.4	)		(14,145	)		1.9
Change in valuation allowances		119,592			(23.2	)		94,668			(14.5	)		133,668			(17.9	)
Tax credits		(11,566	)		2.2			(19,966	)		3.0			(20,005	)		2.6
Share Based Compensation		(26,881	)		5.1			—			—			—			—
Change in state apportionment		—			—			(35	)		—			—			—
Loss on debt conversion		—			—			6,626			(1.0	)		19,548			(2.6	)
Permanent and other		2,889			(0.1	)		(3,078	)		0.5			(731	)		0.1
Effective income tax provision	$	2,132			(0.4	)	$	669			(0.1	)	$	352			(0.1	)

The Company’s effective income tax rate for the year ended December 31, 2023 compared to the year ended December 31, 2022 increased primarily as a result of operations in state jurisdictions.

The Company accounts for income taxes in accordance with ASC Topic 740. Deferred income tax assets and liabilities are determined based upon temporary differences between the financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse.

The following table presents the principal components of the Company’s deferred tax assets and liabilities (in thousands):


	December 31,
	2023			2022
Deferred tax assets:
Intangible assets	$	192,444		$	187,839
Share-based compensation		31,712			29,673
Net operating loss carryforwards		329,135			228,985
Research and development credits		67,667			57,419
Orphan drug credits		34,023			30,160
Development derivative liability		75,190			79,374
Convertible debt		5,582			6,850
Fixed Assets		18			—
Lease liability		2,888			4,304
Accruals		17,401			16,272
Total deferred tax assets		756,060			640,876
Deferred tax liabilities:
Fixed assets		—			(91	)
Right-of-use asset		(2,672	)		(4,032	)
481(a) adjustment		—			(233	)
Total deferred tax liabilities		(2,672	)		(4,356	)
Net deferred tax assets before allowance:		753,388			636,520
Less valuation allowance		(753,388	)		(636,520	)
Net deferred tax assets	$	—		$	—

The Tax Cuts and Jobs Act (TCJA) requires taxpayers to capitalize and amortize research and development (R&D) expenditures under section 174 for tax years beginning after December 31, 2021. This rule became effective for the Company on January 1, 2022 and resulted in the capitalization of R&D costs of approximately $42.3 million and $47.6 million for tax year ending December 31, 2023 and 2022, respectively. The Company will amortize these costs for tax purposes over 5 years if the R&D was performed in the U.S. and over 15 years if the R&D was performed outside the U.S.

ASC Topic 740 requires a valuation allowance to reduce the deferred tax assets reported if, based on the weight of available evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. After consideration of all the evidence, both positive and negative, the Company has recorded full valuation allowances against its domestic and foreign deferred tax assets on December 31, 2023, because management has determined that is it more likely than not that these assets will not be realized. The valuation allowance increased by $116.9 million from December 31, 2022 to December 31, 2023, primarily due to increases in operating losses and research and development tax credits.

On December 31, 2023, the Company had approximately $494.1 million, $524.0 million and $1,663.3 million of federal, state and foreign net operating loss carryforward, respectively. On December 31, 2022, the Company had approximately $312.8 million, $395.4 million and $1,204.7 million of federal, state and foreign net operating loss carryforward, respectively. The Company also had federal and state research and development tax credit carryforwards $85.7 million and $20.2 million, respectively of as of December 31, 2023. Federal net operating loss carryforward in the amount of $449.8 million may be carried forward indefinitely. The remaining federal and state net operating loss, research and development tax credit carryforwards begin to expire in 2025. The Company’s foreign net operating loss carryforwards will begin to expire in 2027.

Under the provisions of the Internal Revenue Code (“IRC”), the net operating loss (“NOL”), and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. NOL and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant stockholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the IRC, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has completed several financings since its inception that it believes may have resulted in a change in control as defined by Sections 382 and 383 of the IRC.

The Company does not have any unrecognized tax benefits during any periods presented and does not expect this to significantly change in the next twelve months. There were no interest and penalties recorded in the statement of operations during any period and no amounts accrued for interest and penalties on December 31, 2023 or 2022.

The Company and its subsidiaries file income tax returns in the United States, as well as various state and foreign jurisdictions. Generally, the tax years 2020 through 2022 remain open and subject to examination by the major taxing jurisdictions to which the Company is subject. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service, or state or foreign tax authorities, to the extent utilized in a future period.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Income Taxes - Schedule of Reconciliation Between U.S. Federal Statutory Rate and Effective Tax rate (Detail)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Statutory U.S. federal income tax, Percentage of income before income taxes	21.00%	21.00%	21.00%
Foreign tax rate differential	(8.00%)	(7.70%)	(5.20%)
State income taxes, net of federal benefit, Percentage of income before income taxes	2.60%	(1.40%)	1.90%
Change in valuation allowances, Percentage of income before income taxes	(23.20%)	(14.50%)	(17.90%)
Tax credits, Percentage of income before income taxes	2.20%	3.00%	2.60%
Share Based Compensation	5.10%
Loss on debt conversion		(1.00%)	(2.60%)
Permanent and other	(0.10%)	0.50%	0.10%
Effective income tax provision, Percentage of income before income taxes	(0.40%)	(0.10%)	(0.10%)

Equity Incentive Plans - Summary of Share-based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation expense	$ 105,945	$ 91,085	$ 70,667
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation expense	45,644	42,052	30,586
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation expense	$ 60,301	$ 49,033	$ 40,081

Product Revenues, Accounts Receivable, and Reserves for Product Sales - Schedule of Disaggregation of Product Revenue by Major Source (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Total product revenue, net	$ 396,591	$ 75,422	$ 66,563
EMPAVELI
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Total product revenue, net	91,033	65,092	15,147
SYFOVRE [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Total product revenue, net	275,248
Product revenue, net [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Total product revenue, net	$ 366,281	$ 65,092	$ 15,147

- Definition

+ References

+ Details

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”).

Revenue Recognition

The Company’s revenues consist of product sales of EMPAVELI and SYFOVRE and revenue derived from its collaboration arrangement with Sobi. See Note 12, License and Collaboration Agreements for further discussion related to the Sobi Collaboration and License Agreement.

The Company accounts for contracts with its customers in accordance with ASC Topic 606, Revenue from Contracts with Customers, (“ASC 606”). Pursuant to ASC 606, for arrangements or transactions between participants determined to be within the scope of the contracts with customers guidance, the Company performs the following five steps to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation.

Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset. For performance obligations that are satisfied over time, the Company recognizes revenue using an input or output measure of progress that best depicts the satisfaction of the relevant performance obligation.

Product Revenue

The Company’s revenue from net product sales was generated in the United States following the FDA’s approval for marketing of EMPAVELI for the treatment of PNH in May 2021 and SYFOVRE in February 2023. The Company sells EMPAVELI and SYFOVRE principally through arrangements with specialty pharmacies (“SPs”) and specialty distributors (“SDs”), who are the Company’s customers. The customers subsequently resell the product to patients and health care providers. The Company applies the ASC 606 five step process discussed above to the contracts with SPs and SDs. The Company provides limited right of return to the customers in cases of shipment errors or expiring or defective products. Product revenues are recognized when the customers take control of the product, which typically occurs upon delivery to the customers.

The Company recognizes revenue from product sales at the net sales price which includes estimates of variable consideration for which reserves are established and reflects each of these as a reduction to revenue. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which the Company is entitled based on the terms of the contract. The amount of variable consideration that is included in the transaction price may be constrained. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from estimates, the Company may need to adjust its estimates, which would affect net revenue in the period of adjustment. The following are the Company’s significant categories of variable consideration:

Distribution Fees: Distribution fees include distribution service fees paid to SPs and SDs based on a contractually fixed percentage of the wholesale acquisition cost (WAC). The Company does not receive a distinct good or service in exchange for the payment. Distribution fees are recorded as an offset to revenue based on contractual terms at the time revenue from the sale is recognized.

Chargebacks: Chargebacks are discounts and fees related to contracts with various third-party payers including pharmacy benefit managers, private healthcare insurers and government healthcare programs that purchase from SDs at a discounted price. SDs charge back to the Company the difference between the price initially paid by SDs and the discounted price paid to SDs by these entities. The Company issues credit notes for the chargeback which are applied to future sales.

Product Returns: Consistent with industry practice, the Company offers SPs and SDs limited product return rights for shipment errors or expiring or defective products; provided that the return is within a specified period around the product expiration date as set

forth in the applicable individual distribution agreement. The Company does not allow product returns for product that has been dispensed to a patient. As the Company receives inventory reports from SPs and SDs and has visibility into the inventory distribution channel, it is able to make a reasonable estimate of future potential product returns based on this on-hand channel inventory data and sell-through data obtained from SPs and SDs. In arriving at its estimate for product returns, the Company also considers historical product returns (to the extent available), the underlying product demand, and industry data specific to the specialty pharmaceutical distribution industry.

Licensing and Collaboration Revenue

The Company analyzes license and collaboration arrangements pursuant to ASC Topic 808, Collaborative Arrangement Guidance and Considerations, (“ASC 808”) to assess whether such arrangements, or transactions between arrangement participants, involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities or are more akin to a vendor-customer relationship. In making this evaluation, the Company considers whether the activities of the collaboration are considered to be distinct and deemed to be within the scope of the collaborative arrangement guidance or if they are more reflective of a vendor-customer relationship and, therefore, within the scope of ASC 606. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement.

For elements of collaboration arrangements that are not accounted for pursuant to guidance in ASC 606, an appropriate recognition method is determined and applied consistently, generally by analogy to the revenue from contracts with customers guidance. Amounts related to transactions with a counterparty in a collaborative arrangement that is not a customer are presented as collaboration revenue and in a separate line item from revenue recognized from contracts with customers, if any, in the consolidated statements of operations.

Pursuant to ASC 606, for arrangements or transactions between arrangement participants determined to be within the scope of the contracts with customers guidance, the Company performs the five-step process discussed above to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations.

We evaluate the performance obligations promised in the contract that are based on goods and services that will be transferred to the customer and determine whether those obligations are both (i) capable of being distinct and (ii) distinct in the context of the contract. Goods or services that meet these criteria are considered distinct performance obligations. The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential transaction price and the likelihood that the transaction price will be received. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and, if so, these options are considered performance obligations. The Company has not currently identified any such material rights.

After contract inception, the transaction price is reassessed at every period end and updated for changes such as resolution of uncertain events. Any change in the overall transaction price is allocated to the performance obligations on the same methodology as at contract inception.

See Note 12, License and Collaboration Agreements, for further discussion related to the Sobi collaboration agreement.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: development liability, accrued expenses, prepaid expenses, convertible debt, reserves for variable consideration, reserves for excess or obsolete inventories, and income taxes.

Fair Value of Financial Instruments

The Company is required to disclose information on the fair value of financial instruments and inputs that enable an assessment of the fair value. The three levels of the fair value hierarchy prioritize valuation inputs based upon the observable nature of those inputs as follows:

Level 1 – Quoted prices in active markets for identical assets or liabilities;

Level 2 – Inputs other than quoted prices included within level 1 that are observable for the asset or liability, either directly or indirectly;

Level 3 – Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability.

The Company’s financial instruments, in addition to those presented in Note 8, Long-term Debt, and Note 11, Fair Value Measurements, include cash and cash equivalents, accounts payable and accrued liabilities. Management believes that the carrying amounts of cash and cash equivalents, accounts payable and accrued expenses approximate the fair value due to the short-term nature of those instruments.

Cash and Cash Equivalents

Cash and cash equivalents are defined as cash in banks and investment instruments having maturities of three months or less from their acquisition date. The carrying amounts reported in the consolidated balance sheets for cash and cash equivalents are valued at cost, which approximates the fair value. See Note 11, Fair Value Measurements, for additional information.

Accounts Receivable

The Company’s accounts receivable primarily arise from product sales. They are generally stated at the invoiced amount and do not bear interest. The accounts receivable from product sales represents receivables due from the Company’s SPs or SDs. The Company has had no historical write offs of its accounts receivable as of December 31, 2023, and its payment terms are generally 30-65 days for EMPAVELI and 60-150 days for SYFOVRE. The Company monitors the financial performance and creditworthiness of its customers and provides reserves against trade receivables for expected credit losses that may result from a customer’s inability to pay. Amounts determined to be uncollectible are written-off against the established reserve. As of December 31, 2023 and 2022, the credit profiles for the Company’s customers were deemed to be in good standing and an allowance for credit losses was not considered necessary.

Inventory

Inventory is recorded at the lower of cost or net realizable value, with cost determined on a first-in, first-out basis. Inventory costs include third-party contract manufacturing, third-party packaging services, and freight. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess and obsolete inventories to their estimated realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded within cost of sales. The determination of whether inventory costs will be realizable requires estimates by management. If actual market conditions are less favorable than projected by management, additional write-downs of inventory may be required which would be recorded as a cost of sales in the consolidated statements of operations and comprehensive loss.

Prior to regulatory approval of its product candidates, the Company expensed costs associated with the manufacturing of its product candidates to research and development expense unless the Company was reasonably certain such costs have future

commercial use and net realizable value. When the Company believes regulatory approval and subsequent commercialization of its product candidates is probable, and the Company also expects future economic benefit from the sales of the product candidates to be realized, the Company will then capitalize the costs of production as inventory. Inventory that can be used in either the production of clinical or commercial product is expensed as research and development expense when selected for use in a clinical manufacturing campaign.

Prior to receiving FDA approval for EMPAVELI on May 14, 2021, the Company included in research and development expense the costs associated with the manufacture of EMPAVELI inventory to be sold upon commercialization. As a result, the manufacturing costs related to the EMPAVELI inventory build-up incurred before FDA approval were expensed in a prior period and are, therefore, excluded from the cost of goods sold and inventory. As of December 31, 2023, the remaining pre-FDA approved inventory was $19.4 million, which primarily consisted of raw materials.

Shipping and handling costs for product shipments are recorded as incurred in cost of sales along with costs associated with manufacturing the product and any inventory write-downs.

Development Liability

From December 15, 2021 and thereafter until the final annual payment due December 2027, the development liability will be accreted from its initial carrying amount to the total payment amount using the effective interest rate method under ASC 835 over the remaining life of the SFJ agreement as defined in Note 6. The difference between the carrying amount and the total payment amount is presented as discount to the development liability. The accretion is recorded as interest expense in the consolidated income statement.

Foreign Currency

The functional currency of each of the Company’s subsidiaries is its local currency, except for the wholly owned subsidiaries in Switzerland and Netherlands where the functional currency is the U.S. dollar. Revenues and expenses of the subsidiaries have been translated into U.S. dollars at average exchange rates prevailing during the respective periods. Assets and liabilities have been translated at the rates of exchange on the balance sheet date. The resulting translation gain and loss adjustments are recorded directly as a separate component of stockholders’ equity.

Research and Development

Costs incurred in connection with research and development activities are expensed as incurred. Research and development expenses include (i) employee-related expenses, including salaries, benefits, travel and share-based compensation expense; (ii) external research and development expenses incurred under arrangements with third parties, such as contract research and contract manufacturing organizations, investigational sites and consultants, including share-based compensation expense for consultants; (iii) the cost of acquiring, developing and manufacturing clinical study materials; and (iv) costs associated with preclinical and clinical activities and regulatory operations.

The Company enters into consulting, research and other agreements with commercial entities, researchers, universities and others for the provision of goods and services. Such arrangements are generally cancellable upon reasonable notice and payment of costs incurred. Costs are considered incurred based on an evaluation of the progress to completion of specific tasks under each contract using information and data provided by the Company’s clinical sites and vendors. These costs consist of direct and indirect costs associated with specific projects, as well as fees paid to various entities that perform certain research on behalf of the Company.

Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management’s estimates of the work performed under service agreements, milestones achieved and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly.

Income Taxes

The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided if, based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The

determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position, as well as consideration of the available facts and circumstances. As of December 31, 2023 and 2022, the Company did not have any significant uncertain tax positions.

Share-Based Compensation - Options

The Company measures stock-based compensation cost at the accounting measurement date based on the fair value of the option and recognizes the expense related to awards to employees on a straight-line basis over the requisite service period of the option, which is typically the vesting period. Forfeitures are recognized as they occur.

The Company estimates the fair value of each option using the Black-Scholes option pricing model that considers the fair value of its common stock, the exercise price, the expected life of the option, the expected volatility of its common stock, expected dividends on its common stock, and the risk-free interest rate over the expected life of the option. The Company uses the simplified method described in the SEC's Staff Accounting Bulletin No. 107, Share-Based Payment, to determine the expected life of the option grants. The estimate of expected volatility is based on a review of the historical volatility of similar publicly held companies in the biotechnology field over a period commensurate with the option's expected term. The Company has never declared or paid any cash dividends on its common stock and does not expect to do so in the foreseeable future. Accordingly, it uses an expected dividend yield of zero. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant valuation for a period commensurate with the option's expected term. These assumptions are subjective and changes in them could significantly impact the value of the option and hence the related compensation expense.

Concentrations of Credit Risk

Financial instruments that potentially subject the Company to concentrations of credit risk include cash, cash equivalents, and marketable securities. The Company is exposed to credit risk in the event of default by the financial institutions holding its cash and the issuers of its cash equivalents and marketable securities. The Company maintains its cash, cash equivalents and marketable securities with highly-rated, federally-insured financial institutions. At times, such amounts may exceed federally-insured limits. The Company has not experienced any losses on its deposits since inception, and management believes that minimal credit risk exists with respect to these financial institutions.

Net Loss per Share

Basic net loss per common share is calculated by dividing net loss by the weighted-average shares outstanding during the period. For purposes of the diluted net loss per share calculation, convertible notes and common stock options are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.

Comprehensive Loss

The Company’s components of comprehensive loss other than its net loss, are foreign currency gains/losses recorded from the remeasurement of the long-term intra-entity loan transaction to the Company’s wholly owned subsidiaries, foreign currency gain/loss from the translation of the Company’s wholly owned subsidiaries into U.S. dollars, unrealized gains and losses on marketable securities, and actuarial gains (losses) and prior service costs in connection with the Company's defined benefit plan.

Recent Accounting Pronouncements

In December 2023, the Financial Accounting Standards Board ("FASB") issued an amendment to the accounting guidance on income taxes which requires entities to provide additional information in the rate reconciliation and additional disaggregated disclosures about income taxes paid. This guidance requires public entities to disclose in their rate reconciliation table additional categories of information about federal, state, and foreign income taxes and to provide more details about the reconciling items in some categories if the items meet a quantitative threshold. The guidance is effective for annual periods beginning after December 15, 2024. The Company is currently evaluating this guidance to determine the impact it may have on its consolidated financial statements disclosures.

In November 2023, the FASB issued an amendment to the accounting guidance on segment reporting. The amendments require disclosure of significant segment expenses and other segment items and requires entities to provide in interim periods all disclosures about a reportable segment's profit or loss and assets that are currently required annually. The amendment also requires disclosure of the title and position of the chief operating decision maker ("CODM") and an explanation of how the CODM uses the reported measure(s) of segment profit or loss in assessing segment performance and deciding how to allocate resources. The guidance is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15,

2024. Retrospective application is required, and early adoption is permitted. The Company is currently evaluating the impact the guidance will have on its consolidated financial statements.

Development Liability - Summary of Development Liability (Detail) - SFJ Agreement [Member] - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development liability	$ 366,000	$ 421,500
Less: Unamortized discount to development liability	(50,353)	(76,349)
Less: Current portion of development liability, net of discount	(75,830)	(29,504)
Total long term development liability	$ 239,817	$ 315,647
Effective Interest Rate	7.91%	7.91%

Leases (Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Schedule of Additional Information Related to Operating Lease Assets and Liabilities

Additional information related to the operating lease assets and liabilities is as follows (in thousands):


	December 31,			December 31,
	2023			2022
Operating lease assets	$	16,745		$	18,747
Operating lease liabilities	$	17,895		$	19,977
Weighted average remaining term in years		2.83			3.57
Weighted average discount rate used to measure outstanding lease liabilities		7.20	%		7.26	%

Supplemental Cash Flow Information Related to Operating Leases

Supplemental cash flow information related to operating leases for the years ended December 31, 2023, 2022 and 2021 is as follows (in thousands):


	2023		2022		2021
Operating cash flows from operating leases	$	7,939	$	7,375	$	5,989
Operating lease assets obtained in exchange for lease obligations		2,700		—	$	5,675

Maturity of Operating Lease Liabilities

The maturity of the Company’s operating lease liabilities as of December 31, 2023 are as follows (in thousands):


2024	$	7,393
2025		6,238
2026		5,299
2027		859
Total future minimum lease payments		19,789
Less imputed interest		(1,894	)
Total operating lease liabilities	$	17,895

Leases - Schedule of Additional Information Related to Operating Lease Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Operating lease assets	$ 16,745	$ 18,747
Operating lease liabilities	$ 17,895	$ 19,977
Weighted average remaining term in years	2 years 9 months 29 days	3 years 6 months 25 days
Weighted average discount rate used to measure outstanding lease liabilities	7.20%	7.26%

Fair Value Measurements

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair Value Measurements

11. Fair Value Measurements

Level 1 – Quoted prices in active markets for identical assets or liabilities;

Level 2 – Inputs other than quoted prices included within level 1 that are observable for the asset or liability, either directly or indirectly;

Level 3 – Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability.

The following table presents the fair value of financial instruments recorded originally at amortized cost or fair value and not re-measured on a recurring basis (in thousands):


		December 31, 2023
Balance Sheet Classification:	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents:	Money market funds	$	276,391	$	—	$	—	$	276,391
Total Financial Assets		$	276,391	$	—	$	—	$	276,391

		December 31, 2022
Balance Sheet Classification:	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents:	Money market funds	$	527,728	$	—	$	—	$	527,728
Total Financial Assets		$	527,728	$	—	$	—	$	527,728

The Company's Convertible Notes and development liability are financial instruments that are reported in the consolidated financial statements at historical cost. The Convertible Notes are Level 1 within the fair value level hierarchy as of December 31, 2023 and December 31, 2022. The fair value of the Convertible Notes was $140.8 million as of December 31, 2023 and $143.9 million as of December 31, 2022. The Convertible Notes accrue a semi-annual coupon at an annual rate of 3.5%, which was included in accrued expenses in the consolidated balance sheets as of December 31, 2023 and December 31, 2022.

The fair value of the development liability was $306.9 million and $315.8 million as of December 31, 2023 and December 31, 2022, respectively. The development liability is Level 2 within the fair value hierarchy based on the discounting of fixed cash flows using an observed bond yield for borrowers with similar credit rating.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Long-term Debt (Tables)

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Schedule of Outstanding Balance of Convertible Notes

The outstanding balance of the Convertible Notes as of December 31, 2023 and 2022 consisted of the following (in thousands):


	December 31,
	2023			2022
Liability
Principal		93,897			93,897
Less: debt discount and issuance costs, net		(864	)		(1,161	)
Net carrying amount		93,033			92,736

Schedule of Interest Expense Recognized Related to Convertible Notes

The following table sets forth total interest expense recognized related to the Convertible Notes during the twelve months ended December 31, 2023, 2022 and 2021 (in thousands):


	Year Ended December 31,
		2023		2022		2021
Amortization of debt issuance costs			297		459		964
Contractual interest expense			3,286		5,248		11,086
Total interest expense		$	3,583	$	5,707	$	12,050

Schedule of Future Minimum Payments on Convertible Notes Payable

Future minimum payments on Convertible Notes payable as of December 31, 2023 is as follows (in thousands):


2024	$	3,286
2025		3,286
2026		96,225
Total future minimum payments		102,797
Less: interest		(8,900	)
Less: debt discount and issuance costs, net		(864	)
Less: current portion		—
Convertible senior notes		93,033