0001564590-21-021318 | 10-Q | XBRL Viewer | Apellis Pharmaceuticals INC

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2021	Apr. 23, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Registrant Name	APELLIS PHARMACEUTICALS, INC.
Entity Central Index Key	0001492422
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
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 Common Stock, Shares Outstanding		80,496,771
Entity Incorporation, State or Country Code	DE
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false
Security 12b Title	Common Stock, $0.0001 par value per share
Trading Symbol	APLS
Security Exchange Name	NASDAQ

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 265,435	$ 565,779
Marketable securities	458,237	311,869
Prepaid assets	17,203	11,400
Restricted cash	1,552	1,266
Other current assets	31,198	26,878
Total current assets	773,625	917,192
Non-current Assets:
Right-of-use assets	22,518	17,719
Property and equipment, net	7,077	6,803
Other assets	6,909	18,855
Total assets	810,129	960,569
Current liabilities:
Accounts payable	4,158	8,477
Accrued expenses	69,398	111,935
Current portion of development derivative liability	6,212	4,230
Current portion of right of use liabilities	3,902	3,685
Total current liabilities	83,670	128,327
Long-term liabilities:
Convertible senior notes	386,152	358,830
Development derivative liability	268,740	253,638
Operating lease liabilities	19,909	15,217
Total liabilities	758,471	756,012
Commitments and contingencies (Note 13)
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized, and zero shares issued and outstanding at March 31, 2021 and December 31, 2020	0	0
Common stock, $0.0001 par value; 200,000 shares authorized at March 31, 2021 and December 31, 2020; 80,438 shares issued and outstanding at March 31, 2021, and 76,130 shares issued and outstanding at December 31, 2020	8	8
Additional paid-in capital	1,147,263	1,131,013
Accumulated other comprehensive loss	(1,620)	(117)
Accumulated deficit	(1,093,993)	(926,347)
Total stockholders' equity	51,658	204,557
Total liabilities and stockholders' equity	$ 810,129	$ 960,569

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
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	80,438,000	76,130,000
Common stock, outstanding	80,438,000	76,130,000

Condensed Consolidated Statements of Operations and Comprehensive Income/(Loss) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating expenses:
Research and development	$ 84,012	$ 69,282
General and administrative	40,579	29,504
Net operating loss	(124,591)	(98,786)
Loss on conversion of debt	(39,487)
Loss from remeasurement of development derivative liability	(17,084)	(68,406)
Interest income	134	2,275
Interest expense	(4,175)	(3,919)
Other income, net	1,544	14
Net loss	(183,659)	(168,822)
Other comprehensive loss:
Unrealized gain on marketable securities	79	1,394
Foreign currency loss	(1,582)	(230)
Total other comprehensive gain/ loss	(1,503)	1,164
Comprehensive loss, net of tax	$ (185,162)	$ (167,658)
Net loss per common share, basic and diluted	$ (2.32)	$ (2.29)
Weighted-average number of common shares used in net loss per common share, basic and diluted	79,219	73,720

Condensed Consolidated Statements of Changes in Stockholder's Equity (Unaudited) - USD ($) $ 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 Income (Loss) [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]
Beginning balance at Dec. 31, 2019	$ 34,229		$ 6	$ 615,850		$ (154)	$ (581,473)
Beginning balance, Shares at Dec. 31, 2019			63,938
Issuance of common stock in follow-on offering, net of offering costs	381,458		$ 1	381,457
Issuance of common stock in follow-on offering, shares			10,925
Issuance of common stock upon exercise of stock options	1,674			1,674
Issuance of common stock upon exercise of stock options, shares			559
Share-based compensation expense	9,294			9,294
Unrealized gain on marketable securities	1,394					1,394
Net loss	(168,822)						(168,822)
Foreign currency loss	(230)					(230)
Ending balance at Mar. 31, 2020	258,997		$ 7	1,008,275		1,010	(750,295)
Ending balance, Shares at Mar. 31, 2020			75,422
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 [Extensible List]	apls:AccountingStandardsUpdate202006Member
Issuance of shares in exchange of 2019 Convertible Notes, including issuance costs	$ 162,258			162,258
Issuance of shares in exchange of 2019 Convertible Notes, including issuance costs. shares			3,976
Forfeiture of accrued interest in exchange of 2019 Convertible Notes	1,668			1,668
Issuance of common stock upon exercise of stock options	2,588			2,588
Issuance of common stock upon exercise of stock options, shares			285
Vesting of restricted stock units, net of shares withheld for taxes	(956)			(956)
Vesting of restricted stock units, net of shares withheld for taxes. shares			47
Share-based compensation expense	16,439			16,439
Unrealized gain on marketable securities	79					79
Net loss	(183,659)						(183,659)
Foreign currency loss	(1,582)					(1,582)
Ending balance at Mar. 31, 2021	$ 51,658		$ 8	$ 1,147,263		$ (1,620)	$ (1,093,993)
Ending balance, Shares at Mar. 31, 2021			80,438

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating Activities
Net loss	$ (183,659)	$ (168,822)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	16,439	9,294
Loss on conversion of debt	39,487
Loss from remeasurement of development derivative liability	17,084	68,406
Forfeiture of accrued interest in exchange of convertible notes	1,668
Amortization of right-of-use assets	112	57
Depreciation expense	282	85
Amortization of debt discounts	360
Amortization of discounts for convertible notes, net of financing costs		1,994
Changes in operating assets and liabilities:
Prepaid assets	(5,819)	(3,004)
Other current assets	(4,242)	(671)
Other assets	11,946	(460)
Accounts payable	(4,170)	(5,237)
Accrued expenses	(42,802)	(9,991)
Net cash used in operating activities	(153,314)	(108,349)
Investing Activities
Purchase of property and equipment	(484)	(435)
Purchase of available-for-sale securities	(171,281)	(227,419)
Proceeds from maturity of available-for-sale securities	25,000
Net cash used in investing activities	(146,765)	(227,854)
Financing Activities
Proceeds from issuance of common stock, net of issuance costs		381,593
Proceeds from development derivative liability		20,000
Proceeds from exercise of stock options	2,588	1,674
Payments of employee tax withholding related to equity-based compensation	(956)
Net cash provided by financing activities	1,632	403,267
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(1,611)	(152)
Net increase in cash, cash equivalents and restricted cash	(300,058)	66,912
Cash, cash equivalents and restricted cash at beginning of period	567,045	351,985
Cash, cash equivalents and restricted cash at end of period	266,987	418,897
Reconciliation of cash, cash equivalents and restricted cash to the consolidated balance sheets:
Cash and cash equivalents	265,435	417,881
Restricted cash	1,552	1,016
Cash, cash equivalents and restricted cash at end of period	266,987	418,897
Supplemental Disclosure of Financing Activities
Cash paid for Interest	6,893	$ 3,829
2019 Convertible Notes exchanged for common stock	$ 126,129

Nature of Organization and Operations

3 Months Ended

Mar. 31, 2021

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 clinical-stage biopharmaceutical company focused on the development of novel therapeutic compounds to treat disease 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 and has its principal office 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 and developing its product candidates.

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”). Additionally, the Company is subject to risks arising from the Coronavirus Disease 2019 (COVID-19) pandemic, which could have adverse effects upon its business and operations, including on its ability to initiate, conduct and complete clinical trials, delay the initiation of planned and future clinical trials and could disrupt regulatory activities.

Adoption of ASU 2020-06 Debt – Debt with Conversion and Other Options (Subtopic 470-20)

Effective January 1, 2021, the Company early adopted ASU 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) which reduces complexity in applying GAAP to certain financial instruments with characteristics of liability and equity. The ASU removes the guidance that requires entities to account for beneficial conversion features and cash conversion features in equity, separately from the host convertible debt or preferred stock. The ASU further revises the guidance to require entities to calculate diluted earnings per share for convertible instruments by using the if-converted method. In addition, entities must presume share settlement for purposes of calculating diluted earnings per share when an instrument may be settled in cash or shares. The impact of the adoption of the statement increased net debt outstanding and decreased net equity by $149.7 million as of January 1, 2021. Of the $149.7 million decrease to net equity, $16.0 million was recorded to retained earnings. See Note 5, Long Term Debt for additional information.

Convertible Notes Exchange

In January 2021, the Company entered into separate, privately negotiated exchange agreements to modify the conversion terms with certain holders of its convertible notes issued in September 2019 (the “2019 Convertible Notes”). Under the terms of these exchange agreements, the holders exchanged approximately $126.1 million in aggregate principal amount of 2019 Convertible Notes held by them for an aggregate of 3,906,869 shares of common stock issued by the Company. The Company also issued 69,491 shares for settlement of issuance costs paid to the Company’s advisor. The Company recognized a total loss on conversion of debt in the unaudited condensed consolidated statement of operations of $39.5 million. As of March 31, 2021, the Company held as treasury Convertible Notes the $126.1 million principal amount of exchanged notes and such notes have not been cancelled. See Note 5, Long Term Debt for additional information.

Liquidity and Going Concern

The accompanying unaudited condensed consolidated financial statements have been prepared on the basis of the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. As of April 28, 2021, the date of issuance of these unaudited condensed consolidated financial statements, the Company believes that its cash and cash equivalents of $265.4 million and marketable securities of $458.2 million as of March 31, 2021 will be sufficient to fund its operations and capital expenditure requirements for at least the next twelve months from the date of issuance of these unaudited condensed consolidated

financial statements. The future viability of the Company beyond that point is dependent on its ability to raise additional capital to finance its operations.

The Company is subject to risks common to other life science companies in the development stage including, but not limited to, uncertainty of product development and commercialization, lack of marketing and sales history, development by its competitors of new technological innovations, dependence on key personnel, market acceptance of products, product liability, protection of proprietary technology, ability to raise additional financing, and compliance with FDA and other government regulations. If the Company does not successfully commercialize any of its product candidates, it will be unable to generate recurring product revenue or achieve profitability. The Company’s plans to meet its short-term and longer-term operating cash flow requirements include obtaining additional funding.

There are uncertainties associated with the Company’s ability to (1) obtain additional debt or equity financing on terms that are favorable to the Company (2) enter into collaborative agreements with strategic partners to obtain funding, and (3) succeed in its future operations. If the Company is not able to obtain the required funding for its operations, or is not able to obtain funding on a timely basis on terms that are favorable to the Company, it could be forced to delay, reduce or eliminate its research and development programs or future commercialization efforts and its business could be materially harmed.

Basis of Presentation

3 Months Ended

Mar. 31, 2021

Accounting Policies [Abstract]

Basis of Presentation

2. Basis of Presentation

The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Apellis Australia Pty Ltd, Apellis Bermuda Limited, Apellis Germany GmbH, Apellis Ireland Ltd, Apellis Netherlands B.V., Apellis Switzerland GmbH, Apellis UK Limited, APL DEL Holdings LLC, APL Sales Corp I, LLC, APL PRG I, Corp. and Apellis MA Securities Corp. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”), for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP have been condensed or omitted and, accordingly, the consolidated balance sheet as of December 31, 2020 has been derived from audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair presentation of the Company’s financial information. The results of operations for the three months ended March 31, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any other interim period or for any other future year.

The accompanying unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2020 included in the Company’s Annual Report on Form 10-K filed with the SEC on February 25, 2021.

Licensing and Collaboration Revenue

The Company analyzes license and collaboration arrangements pursuant to FASB 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 FASB ASC Topic 606, Revenue from Contracts with Customer, (“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 Company’s 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 following 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.

The Company evaluates 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 11, License and Collaboration Agreements, for further discussion related to the Collaboration and License Agreement with Swedish Orphan Biovitrum AB (Publ) (“Sobi”).

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 5, Long-term Debt, Note 7, Marketable Securities, and Note 9, Fair Value Measurements, include cash and cash equivalents, other receivables, accounts payable and accrued liabilities. Management believes that the carrying amounts of certain cash and cash equivalents, other receivables, 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 condensed consolidated balance sheets for certain cash and cash equivalents are valued at cost, which approximates their fair value. See Note 9, Fair Value Measurements, for additional information.

Restricted Cash

The Company is contingently liable under unused letters of credit with a bank, related to the Company’s customs import bond and facility lease agreements of $1.6 million and $1.3 million as of March 31, 2021 and December 31, 2020, respectively. The Company records as restricted cash the collateral used to secure these letters of credit.

Foreign Currency

The financial position and results of operations of the Company's Australian, Irish and German subsidiaries are measured using the foreign subsidiary's local currency. 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. The financial position and results of operations of the Company’s Swiss subsidiary are measured and reported in U.S. dollars and transactions are translated to U.S. dollars at the end of the period.

Prepaid Assets and Accrued Expenses

3 Months Ended

Mar. 31, 2021

Prepaid Assets And Accrued Expenses [Abstract]

Prepaid Assets And Accrued Expenses

3. Prepaid Assets and Accrued Expenses

Prepaid assets include $14.1 million and $8.0 million of prepaid research and development costs as of March 31, 2021 and December 31, 2020, respectively.

Accrued expenses are as follows (in thousands):

	March 31,		December 31,
	2021		2020
Accrued research and development	$	32,586	$	47,879
Accrued license fee		—		25,050
Accrued payroll liabilities		11,857		22,896
Other		24,955		16,110
Total	$	69,398	$	111,935

Development Derivative Liability

3 Months Ended

Mar. 31, 2021

Research And Development [Abstract]

Development Derivative Liability

4. Development Derivative Liability

On February 28, 2019, the Company entered into a development funding agreement, (the “SFJ Agreement”), with SFJ Pharmaceuticals Group (“SFJ”), under which SFJ agreed to provide funding to the Company to support the development of pegcetacoplan for the treatment of patients with PNH. 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.

On June 7, 2019, the Company and SFJ amended the development funding agreement, (the “SFJ Amendment”). Under the SFJ Amendment, SFJ agreed to make an additional $20.0 million funding payment to the Company to support the development of pegcetacoplan for the treatment of patients with PNH.

As of March 31, 2021, the Company has received a total of $140.0 million from SFJ as the Company met milestones as identified in the agreement. The Company did not receive any funds under the SFJ agreement in 2021. In the three months ended March 31, 2020, the Company received $20.0 million, from SFJ.

Under the SFJ Agreement following regulatory approval by the FDA or EMA for the use of pegcetacoplan as a treatment for PNH the Company will be obligated to pay SFJ an initial payment of up to $5.0 million (or a total of $10.0 million if regulatory approval is granted by the FDA and the EMA) and then up to an additional $226.0 million in the aggregate (or up to $452.0 million if regulatory approval is granted by the FDA and the EMA) in six additional annual payments with the majority of the payments being made from the third anniversary to the sixth anniversary of regulatory approval. Additionally, the Company granted a security interest

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.

The SFJ Agreement is presented as a derivative liability on the condensed consolidated balance sheet and is considered a level three derivative, and, as such, is recorded at fair value and remeasured each quarter. The change in fair value due to the remeasurement of the development derivative liability resulted in a $17.1 million loss and a $68.4 million loss for the three months ended March 31, 2021 and 2020, respectively, recorded on the unaudited condensed consolidated statement of operations. The development derivative liability has a remeasured fair value of $275.0 million on the consolidated balance sheet at March 31, 2021. At March 31, 2021, $6.2 million of the $275.0 million of the development derivative liability fair market value is included in current liabilities.

The following table presents a rollforward of the development derivative liability (in thousands):

	For the Three Months Ended March 31,
	2021		2020
Balance at fair market value, January 1,	$	257,868	$	134,839
Amounts received under the SFJ Agreement and SFJ Amendment		—		20,000
Loss recorded in loss from remeasurement of development derivative liability		17,084		68,406
Balance at fair market value, March 31,	$	274,952	$	223,245

The derivative is valued using a scenario-based discounted cash flow method, whereby each scenario makes assumptions about the probability and timing of cash flows, and such cash flows are present valued using a risk-adjusted discount rate. The analysis is calibrated such that the value of the derivative as of the date of the SFJ Agreement was consistent with an arm’s-length transaction. Key inputs to the level 3 fair value model include (i) the probability and timing of achieving stated development milestones to receive the next tranches of funding, (ii) the probability and timing of achieving FDA and EMA approval, (iii) SFJ’s cost of borrowing (8.0%), and (iv) the Company’s cost of borrowing (11.76%).

SFJ’s implied cost of borrowing was 8.0% and the Company’s implied cost of borrowing was 11.76% as of the reporting date. These implied costs of borrowing were determined assuming the SFJ Agreement was initially executed with arm’s-length terms. If the SFJ Agreement was instead not determined to be an arm’s-length transaction, then implied discount rates could differ.

Long-term Debt

3 Months Ended

Mar. 31, 2021

Debt Disclosure [Abstract]

Long-term Debt

5. 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 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 by the Company. The Company used $28.4 million of the net proceeds from the sale of the 2019 Convertible Notes to pay the cost of the capped call transactions in September 2019 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 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. 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 may not redeem the Convertible Notes. The Company may redeem for cash all or a portion of the Convertible Notes, at its option, on or after September 20, 2023 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 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.

Prior to the adoption of ASU 2020-06 effective January 1, 2021, 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 Convertible Notes aggregate debt issuance costs of $6.0 million were allocated to the liability and equity components in the amounts of $3.7 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.

Effective January 1, 2021, the Company adopted ASU 2020-06 using the modified retrospective method. Upon adoption, the Company increased net debt and reduced net equity by $149.7 million. The $149.7 million consisted of several items. The first item is the reclassification from equity to debt of the residual amounts originally identified as the equity components of the 2019 and 2020 Convertible Notes of $74.9 million and $95.5 million, respectively. The equity component reclassification was offset by the adjustment to retained earnings for the reversal of previous non-cash interest expense recorded for the amortization of the equity components of $17.1 million. The second item is the reclassification from equity to debt of the debt issuance costs originally allocated to equity for the 2019 and 2020 Convertible Notes of $2.4 million and $2.3 million, respectively. The debt issuance costs reclassification was offset by the adjustment to retained earnings for previous amortization of the debt issuance costs recorded of $1.1 million.

In January 2021, the Company entered into separate, privately negotiated exchange agreements to modify the conversion terms with certain holders of its 2019 Convertible Notes. Under the terms of these exchange agreements, the holders exchanged approximately $126.1 million in aggregate principal amount of 2019 Convertible Notes held by them for an aggregate of 3,906,869 shares of common stock issued by the Company. In accordance with ASC topic 470-20, “Debt,– Debt with Conversion and Other Options,” 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. 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 advisor in connection with the conversion transaction. 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. 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 of March 31, 2021, the Company held as treasury Convertible Notes the $126.1 million principal amounts of exchanged notes and such notes had not been cancelled.

Interest expense for the Convertible Notes was $4.2 million and $3.9 million for the three months ended March 31, 2021 and 2020, respectively. For the three months ended March 31, 2021, interest expense included accrued semi-annual coupon payable of $3.8 million and amortization of debt issuance costs of $0.4 million. For the three months ended March 31, 2020 interest expense included the amortization of the discount on the Convertible Notes of $1.9 million, an accrued semi-annual coupon payable of $1.9 million and amortization of debt issuance costs of $0.1 million. As of March 31, 2021, $7.7 million of debt issuance costs was recorded on the unaudited condensed consolidated balance sheet as a reduction to the carrying amount of the Convertible Notes.

The aggregate principal balance of the Convertible Notes, net of unamortized debt issuance costs, as of March 31, 2021 and December 31, 2020 was $386.2 million and $358.8 million respectively.

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, respectively, 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 March 31, 2021 for the 2019 and 2020 Convertible Notes, respectively.

Leases

3 Months Ended

Mar. 31, 2021

Leases [Abstract]

Leases

6. Leases

On January 1, 2019, the Company adopted ASU 2016-02 Leases (Topic 842) using a modified retrospective method. 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 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 of these 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 March 31, 2021 and December 31, 2020, 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):

	March 31,			December 31,
	2021			2020
Operating Lease Assets	$	22,518		$	17,719
Operating Lease Liabilities	$	23,811		$	18,902
Weighted Average Remaining Term in years		5.35		4.66
Weighted Average discount rate used to measure outstanding lease liabilities		7.76	%		7.74	%

For the three months ended March 31, 2021 and 2020, the total lease cost for operating lease expense was $1.3 million and $1.0 million, respectively.

Supplemental cash flow information related to operating leases for the three months ended March 31 is as follows (in thousands):

	2021		2020
Operating cash flows for operating leases	$	1,588	$	968
Operating lease assets obtained in exchange for lease obligations	$	5,675	$	334

The maturities of the Company’s operating lease liabilities as of March 31, 2021 are as follows (in thousands):

2021	$	4,204
2022		5,415
2023		5,480
2024		4,811
2025 and thereafter		9,267
Total future minimum lease payments less		29,177
Imputed interest		(5,366	)
Total operating lease liabilities	$	23,811

Marketable Securities

3 Months Ended

Mar. 31, 2021

Investments Debt And Equity Securities [Abstract]

Marketable Securities

7. Marketable Securities

The amortized cost, gross unrealized holding losses and fair value of available-for-sale debt securities by type of security as of March 31, 2021 and December 31, 2020 were as follows (in thousands):

	As of March 31, 2021
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
U.S. Government-related obligations	$	458,158	$	79	$	—		$	458,237

	As of December 31, 2020
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
U.S. Government-related obligations	$	311,877	$	11	$	(19	)	$	311,869

All available-for-sale securities mature in one year or less.

Other Comprehensive Income and Accumulated Other Comprehensive Income

3 Months Ended

Mar. 31, 2021

Equity [Abstract]

Other Comprehensive Income and Accumulated Other Comprehensive Income

8. Other Comprehensive Income and Accumulated Other Comprehensive Income

The following tables summarize the changes in accumulated other comprehensive income/(loss), by component for the three months ended March 31, 2021 and 2020 (in thousands):

	Unrealized Gains (Losses) from Marketable Securities			Foreign Currency Translation Adjustment			Total Accumulated Other Comprehensive Income (Loss)
Balances, December 31, 2020	$	(8	)	$	(109	)	$	(117	)
Net other comprehensive income (loss)		79			(1,582	)		(1,503	)
Balances, March 31, 2021		71			(1,691	)		(1,620	)

	Unrealized Gains (Losses) from Marketable Securities		Foreign Currency Translation Adjustment			Total Accumulated Other Comprehensive Income (Loss)
Balances, December 31, 2019	$	—	$	(154	)	$	(154	)
Net other comprehensive income (loss)		1,394		(230	)		1,164
Balances, March 31, 2020		1,394		(384	)		1,010

Fair Value Measurements

3 Months Ended

Mar. 31, 2021

Fair Value Disclosures [Abstract]

Fair Value Measurements

9. 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 remeasured on a recurring basis (in thousands):

		March 31, 2021
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents:	Money market funds	$	213,175	$	—	$	—	$	213,175
	Bank certificates of deposit		43,582		—		—		43,582
Total Financial Assets		$	256,757	$	—	$	—	$	256,757

		December 31, 2020
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents	Money market funds	$	427,515	$	—	$	—	$	427,515
	Bank certificates of deposit		43,577		—		—		43,577
Total Financial Assets		$	471,092	$	—	$	—	$	471,092

* The convertible notes were measured and recognized at fair value on the consolidated balance sheet at inception.

The Company’s Convertible Notes are Level 1 category within the fair value level hierarchy at March 31, 2021 due to the adoption of ASU 2020-06. The fair value of the Convertible Notes was $547.3 million at March 31, 2021. At December 31, 2020, the Company’s Convertible Notes were Level 2 category within the fair value level hierarchy. At December 31, 2020, the fair value of debt was determined using broker quotes in a non-active market for valuation. As of December 31, 2020, the debt component of the Company's Convertible Notes was $676.2 million. 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 at March 31, 2021 and December 31, 2020.

The following table presents the fair value of financial instruments recorded at fair value at inception and remeasured on a recurring basis (in thousands):

		March 31, 2021
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Marketable securities:	US government obligations	$	458,237		—		—	$	458,237
Total Financial Assets		$	458,237	$	—	$	—	$	458,237

Financial Liabilities:
Development derivative liability	Development derivative liability	$	—	$	—	$	274,952	$	274,952
Total Financial Liabilities		$	—	$	—	$	274,952	$	274,952

		December 31, 2020
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents	US government obligations	$	89,990	$	—	$	—	$	89,990
Marketable securities:	US government obligations		311,869		—		—		311,869
Total Financial Assets		$	401,859	$	—	$	—	$	401,859

Financial Liabilities:
Development derivative liability	Development derivative liability	$	—	$	—	$	257,868	$	257,868
Total Financial Liabilities		$	—	$	—	$	257,868	$	257,868

The fair value of the SFJ Agreement is presented as a development derivative liability based on level 3 inputs. The derivative is valued using a scenario-based discounted cash flow method, whereby each scenario makes assumptions about the probability and timing of cash flows, and such cash flows are present valued using a risk-adjusted discount rate. The analysis is calibrated such that the value of the derivative as of the date of the SFJ Agreement was consistent with an arm’s-length transaction. Key inputs to the level 3 fair value model include (i) the probability and timing of achieving stated development milestones to receive the next tranches of funding, (ii) the probability and timing of achieving FDA and EMA approval, (iii) SFJ’s cost of borrowing (8.0%), and (iv) the Company’s cost of borrowing (11.76%).

- 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

Income Taxes

3 Months Ended

Mar. 31, 2021

Income Tax Disclosure [Abstract]

Income Taxes

10. Income Taxes

Deferred tax assets and deferred tax liabilities are determined based on temporary differences between the financial reporting and tax bases 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. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Company has recorded a full valuation allowance against its deferred tax assets for the period ended on March 31, 2021.

The Company does not recognize a tax benefit for uncertain tax positions unless it is more likely than not that the position will be sustained upon examination by tax authorities, including resolution of any related appeals or litigation processes, based on the technical merits of the position. The tax benefit that is recorded for these positions is measured at the largest amount of cumulative benefit that has greater than a 50 percent likelihood of being realized upon ultimate settlement. Deferred tax assets that do not meet these recognition criteria are not recorded and the Company recognizes a liability for uncertain tax positions that may result in tax payments. If such unrecognized tax benefits were realized and not subject to valuation allowances, the entire amount would impact the tax provision. The Company has not recorded any amounts for unrecognized tax positions for the period ended on March 31, 2021.

For the three months ended on March 31, 2021 and 2020, the Company did not record any current or deferred income tax expense or benefit.

- 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 + Details

License and Collaboration Agreements

3 Months Ended

Mar. 31, 2021

Organization Consolidation And Presentation Of Financial Statements [Abstract]

License and Collaboration Agreements

11. License and Collaboration Agreements

Sobi Transaction

On October 27, 2020, the Company and its subsidiaries 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 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 collaboration agreement, the Company and Sobi have agreed to collaborate to develop Licensed Products for the treatment of paroxysmal nocturnal hemoglobinuria, cold agglutinin disease, hematopoietic stem cell transplantation-associated thrombotic microangiopathy, C3 glomerulopathy and immune complex membranoproliferative glomerulonephritis, and amyotrophic lateral sclerosis, 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 paroxysmal nocturnal hemoglobinuria in the European Union and the United Kingdom. The Company and Sobi will form several governance committees to oversee the development and manufacture, and to review and discuss the commercialization, of Licensed Products.

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, and to reimburse the Company for up to $80.0 million in development costs. The Company will also be 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. Under the collaboration agreement, the Company remains responsible for its license fee obligations (including royalty obligations) to the University of Pennsylvania as a licensor of the Company and for its payment obligations to SFJ Pharmaceuticals.

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. To date, the Company has not recognized any commercial milestone or royalty revenue resulting from any of our licensing arrangements. Management will periodically assess the elements of the contract and re-evaluate revenue recognition as necessary.

Pursuant to ASC 606, for the year ended December 31, 2020 the Company 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 three months ended March 31, 2021, the Company did not recognize licensing revenue. As of March 31, 2021, the Company recognized $8.1 million for contra-research and development expense in the unaudited condensed consolidated statement of operations related to the $80.0 million reimbursement from Sobi. As of December 31, 2020, the Company had recorded a $43.0 million receivable for contra-research and development reimbursement on the consolidated balance sheet, with $25.0 million and $18.0 million in current and long-term assets, respectively. The Company received a $25.0 million payment from Sobi in January 2021. As of March 31, 2021, the Company has a receivable of $26.1 million for contra-research and development reimbursement from Sobi recognized on the unaudited condensed consolidated balance sheet with $20.0 million recognized in current assets and $6.1 million recognized in other assets.

License Agreements

3 Months Ended

Mar. 31, 2021

Organization Consolidation And Presentation Of Financial Statements [Abstract]

License Agreements

12. License Agreements

In connection with its purchase of assets from Potentia in September 2014, the Company became party to a license agreement with the Trustees of the University of Pennsylvania (“Penn”) as a result of an agreement to purchase substantially all the assets of Potentia Pharmaceuticals, Inc, 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 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 royalty expense owed to Penn related to the Sobi Agreement and another licensing transaction. As of December 31, 2020 the $25.0 million was recognized in accrued expenses on the consolidated balance sheet and recognized in license fees on the consolidated income statement.

In addition to the license agreement with Penn, the Company contracts to conduct research and development activities with third parties. Certain of these contracts commit the Company to pay future milestone payments up to $15.0 million or to pay royalty fees ranging from 3-6% if any of the research results in regulatory approval or commercial revenue for a product.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2021

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

13. Commitments and Contingencies

The Company contracts to conduct research and development activities with third parties. The scope of the services under the research and development contracts can be modified and the contracts cancelled by the Company upon written notice. In some instances, the contracts may be cancelled by the third party upon written notice. If the Company were to cancel these contracts as of March 31, 2021, the Company would be required to pay certain termination costs and other fees of approximately $3.2 million that would be incurred in future periods.

The Company has certain non-cancellable purchase obligations related to the manufacturing of drug substance and drug product, primarily with Bachem Americas, Inc., and Bachem AG, collectively (“Bachem”) for the drug substance for the finished dosage form of pegcetacoplan and with NOF Corporation and NOF America Corporation, collectively, (“NOF”) for a component of pegcetacoplan. As of March 31, 2021, the Company has non-cancellable purchase commitments for 2021 with Bachem and NOF in the amount of approximately $16.4 million and $32.4 million, respectively. Subsequent to March 31, 2021, the Company became obligated for additional non-cancellable purchase commitments to Bachem and NOF for 2021 of approximately $2.9 million and $6.4 million, respectively.

Following regulatory approval by the FDA or EMA of pegcetacoplan for the treatment of PNH, the Company has certain payment and other obligations under the SFJ Agreement, which are discussed above in Note 4.

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. Management does not believe that any such claims would have a material impact on the Company’s consolidated financial statements.

Net Loss per Share

3 Months Ended

Mar. 31, 2021

Earnings Per Share [Abstract]

Net Loss per Share

14. Net Loss per Share

Since the Company was in a loss position for all periods presented, basic net loss per common share is the same as diluted net loss per common share for all periods presented as the inclusion of all potential common shares outstanding would have been anti-dilutive. Convertible notes and shares outstanding presented below were excluded from the calculation of diluted net loss per share, prior to the use of the treasury stock method, as their effect is anti-dilutive (in thousands):

	For the Three Months Ended March 31,
	2021		2020
Convertible notes		9,981		5,575
Common stock options		13,404		9,434
Restricted stock units		949		298
Total		24,334		15,307

Basis of Presentation (Policies)	3 Months Ended
Basis of Presentation (Policies)	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Apellis Australia Pty Ltd, Apellis Bermuda Limited, Apellis Germany GmbH, Apellis Ireland Ltd, Apellis Netherlands B.V., Apellis Switzerland GmbH, Apellis UK Limited, APL DEL Holdings LLC, APL Sales Corp I, LLC, APL PRG I, Corp. and Apellis MA Securities Corp. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”), for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP have been condensed or omitted and, accordingly, the consolidated balance sheet as of December 31, 2020 has been derived from audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair presentation of the Company’s financial information. The results of operations for the three months ended March 31, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any other interim period or for any other future year. The accompanying unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2020 included in the Company’s Annual Report on Form 10-K filed with the SEC on February 25, 2021.
Licensing and Collaboration Revenue	Licensing and Collaboration Revenue The Company analyzes license and collaboration arrangements pursuant to FASB 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 FASB ASC Topic 606, Revenue from Contracts with Customer, (“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 Company’s 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 following 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. The Company evaluates 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 11, License and Collaboration Agreements, for further discussion related to the Collaboration and License Agreement with Swedish Orphan Biovitrum AB (Publ) (“Sobi”).
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 5, Long-term Debt, Note 7, Marketable Securities, and Note 9, Fair Value Measurements, include cash and cash equivalents, other receivables, accounts payable and accrued liabilities. Management believes that the carrying amounts of certain cash and cash equivalents, other receivables, 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 condensed consolidated balance sheets for certain cash and cash equivalents are valued at cost, which approximates their fair value. See Note 9, Fair Value Measurements, for additional information.
Restricted Cash	Restricted Cash The Company is contingently liable under unused letters of credit with a bank, related to the Company’s customs import bond and facility lease agreements of $1.6 million and $1.3 million as of March 31, 2021 and December 31, 2020, respectively. The Company records as restricted cash the collateral used to secure these letters of credit.
Foreign Currency	Foreign Currency The financial position and results of operations of the Company's Australian, Irish and German subsidiaries are measured using the foreign subsidiary's local currency. 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. The financial position and results of operations of the Company’s Swiss subsidiary are measured and reported in U.S. dollars and transactions are translated to U.S. dollars at the end of the period.

- Definition

Disclosure of accounting policy for revenue from contract with customer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130561-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 20
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130566-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130563-203045

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-URI http://asc.fasb.org/topic&trid=49130388

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 20
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130566-203045

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130563-203045

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18823-107790

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 20
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130566-203045

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130564-203045

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 20
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130566-203045

+ Details

Prepaid Assets and Accrued Expenses (Tables)

3 Months Ended

Mar. 31, 2021

Prepaid Assets And Accrued Expenses [Abstract]

Schedule of Accrued Expenses

Accrued expenses are as follows (in thousands):

	March 31,		December 31,
	2021		2020
Accrued research and development	$	32,586	$	47,879
Accrued license fee		—		25,050
Accrued payroll liabilities		11,857		22,896
Other		24,955		16,110
Total	$	69,398	$	111,935

Development Derivative Liability (Tables)

3 Months Ended

Mar. 31, 2021

Research And Development [Abstract]

Schedule of Development Derivative Liability

The following table presents a rollforward of the development derivative liability (in thousands):

	For the Three Months Ended March 31,
	2021		2020
Balance at fair market value, January 1,	$	257,868	$	134,839
Amounts received under the SFJ Agreement and SFJ Amendment		—		20,000
Loss recorded in loss from remeasurement of development derivative liability		17,084		68,406
Balance at fair market value, March 31,	$	274,952	$	223,245

Leases (Tables)

3 Months Ended

Mar. 31, 2021

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):

	March 31,			December 31,
	2021			2020
Operating Lease Assets	$	22,518		$	17,719
Operating Lease Liabilities	$	23,811		$	18,902
Weighted Average Remaining Term in years		5.35		4.66
Weighted Average discount rate used to measure outstanding lease liabilities		7.76	%		7.74	%

Supplemental Cash Flow Information Related to Operating Leases

Supplemental cash flow information related to operating leases for the three months ended March 31 is as follows (in thousands):

	2021		2020
Operating cash flows for operating leases	$	1,588	$	968
Operating lease assets obtained in exchange for lease obligations	$	5,675	$	334

Maturities of Operating Lease Liabilities

The maturities of the Company’s operating lease liabilities as of March 31, 2021 are as follows (in thousands):

2021	$	4,204
2022		5,415
2023		5,480
2024		4,811
2025 and thereafter		9,267
Total future minimum lease payments less		29,177
Imputed interest		(5,366	)
Total operating lease liabilities	$	23,811

Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2021

Investments Debt And Equity Securities [Abstract]

Schedule of Amortized Cost, Gross Unrealized Holding Losses and Fair Value of Available-for-Sale Debt Securities by Type of Security

The amortized cost, gross unrealized holding losses and fair value of available-for-sale debt securities by type of security as of March 31, 2021 and December 31, 2020 were as follows (in thousands):

	As of March 31, 2021
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
U.S. Government-related obligations	$	458,158	$	79	$	—		$	458,237

	As of December 31, 2020
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
U.S. Government-related obligations	$	311,877	$	11	$	(19	)	$	311,869

Other Comprehensive Income and Accumulated Other Comprehensive Income (Tables)

3 Months Ended

Mar. 31, 2021

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 three months ended March 31, 2021 and 2020 (in thousands):

	Unrealized Gains (Losses) from Marketable Securities			Foreign Currency Translation Adjustment			Total Accumulated Other Comprehensive Income (Loss)
Balances, December 31, 2020	$	(8	)	$	(109	)	$	(117	)
Net other comprehensive income (loss)		79			(1,582	)		(1,503	)
Balances, March 31, 2021		71			(1,691	)		(1,620	)

	Unrealized Gains (Losses) from Marketable Securities		Foreign Currency Translation Adjustment			Total Accumulated Other Comprehensive Income (Loss)
Balances, December 31, 2019	$	—	$	(154	)	$	(154	)
Net other comprehensive income (loss)		1,394		(230	)		1,164
Balances, March 31, 2020		1,394		(384	)		1,010

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2021

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 remeasured on a recurring basis (in thousands):

		March 31, 2021
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents:	Money market funds	$	213,175	$	—	$	—	$	213,175
	Bank certificates of deposit		43,582		—		—		43,582
Total Financial Assets		$	256,757	$	—	$	—	$	256,757

		December 31, 2020
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents	Money market funds	$	427,515	$	—	$	—	$	427,515
	Bank certificates of deposit		43,577		—		—		43,577
Total Financial Assets		$	471,092	$	—	$	—	$	471,092

* The convertible notes were measured and recognized at fair value on the consolidated balance sheet at inception.

Fair Value, Recurring [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 at fair value at inception and remeasured on a recurring basis (in thousands):

		March 31, 2021
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Marketable securities:	US government obligations	$	458,237		—		—	$	458,237
Total Financial Assets		$	458,237	$	—	$	—	$	458,237

Financial Liabilities:
Development derivative liability	Development derivative liability	$	—	$	—	$	274,952	$	274,952
Total Financial Liabilities		$	—	$	—	$	274,952	$	274,952

		December 31, 2020
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents	US government obligations	$	89,990	$	—	$	—	$	89,990
Marketable securities:	US government obligations		311,869		—		—		311,869
Total Financial Assets		$	401,859	$	—	$	—	$	401,859

Financial Liabilities:
Development derivative liability	Development derivative liability	$	—	$	—	$	257,868	$	257,868
Total Financial Liabilities		$	—	$	—	$	257,868	$	257,868

Net Loss per Share (Tables)

3 Months Ended

Mar. 31, 2021

Earnings Per Share [Abstract]

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

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

	For the Three Months Ended March 31,
	2021		2020
Convertible notes		9,981		5,575
Common stock options		13,404		9,434
Restricted stock units		949		298
Total		24,334		15,307

Nature of Organization and Operations - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended
	Jan. 01, 2021	Jan. 31, 2021	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Nature Of Organization And Operations [Line Items]
Aggregate principal amount converted			$ 126,129
Total loss on conversion of debt			39,487
Cash and cash equivalents			265,435	$ 565,779	$ 417,881
Marketable securities			458,237	$ 311,869
2019 Convertible Notes [Member] \| Convertible Senior Notes Due 2026 [Member] \| Exchange Agreements [Member]
Nature Of Organization And Operations [Line Items]
Increase (decrease) in net debt		$ (122,800)
Aggregate principal amount converted		$ 126,100	$ 126,100
Additional shares issued for settlement of debt issuance cost paid		69,491
Total loss on conversion of debt		$ 39,500
Common Stock [Member] \| 2019 Convertible Notes [Member] \| Convertible Senior Notes Due 2026 [Member] \| Exchange Agreements [Member]
Nature Of Organization And Operations [Line Items]
Aggregate principal amount converted into shares		3,906,869
ASU 2020-06 [Member]
Nature Of Organization And Operations [Line Items]
Change in accounting principle accounting standards update adopted			true
Change in accounting principle accounting standards update adoption date			Jan. 01, 2021
Increase (decrease) in net debt	$ 149,700
Decrease in net equity	(149,700)
ASU 2020-06 [Member] \| Retained Earnings [Member]
Nature Of Organization And Operations [Line Items]
Decrease in net equity	$ (16,000)

Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Restricted cash	$ 1,552	$ 1,266

Prepaid Assets and Accrued Expenses - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Prepaid Assets And Accrued Expenses [Abstract]
Prepaid research and development	$ 14.1	$ 8.0

Prepaid Assets and Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Prepaid Assets And Accrued Expenses [Abstract]
Accrued research and development	$ 32,586	$ 47,879
Accrued license fee		25,050
Accrued payroll liabilities	11,857	22,896
Other	24,955	16,110
Total	$ 69,398	$ 111,935

Development Derivative Liability - Additional Information (Detail)		3 Months Ended
	Feb. 28, 2019 USD ($) Installment	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Jun. 07, 2019 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Loss from remeasurement of development derivative liability		$ 17,084,000	$ 68,406,000
Development derivative liability		268,740,000		$ 253,638,000
Current portion of development derivative liability		$ 6,212,000		$ 4,230,000
Level 3 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Implied cost of borrowing discount rates		11.76%
SFJ Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from SFJ agreement	$ 60,000,000.0	$ 140,000,000.0	20,000,000.0
Additional funding amount upon achievement of development milestones	$ 60,000,000.0
Number of milestone payments \| Installment	3
Development funding for minimum period of operating expense	10 months
Increase in additional funding for development costs					$ 20,000,000.0
Number of additional annual payments \| Installment	6
Loss from remeasurement of development derivative liability		17,100,000	$ 68,400,000
Development derivative liability		275,000,000.0
Current portion of development derivative liability		$ 6,200,000
SFJ Agreement [Member] \| Level 3 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Implied cost of borrowing discount rates		8.00%
SFJ Agreement [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Obligated to pay initial payment	$ 5,000,000.0
Aggregate amount of additional annual payments	226,000,000.0
SFJ Agreement [Member] \| Regulatory Approval Granted by FDA and EMA [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Obligated to pay initial payment	10,000,000.0
SFJ Agreement [Member] \| Regulatory Approval Granted by FDA and EMA [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate amount of additional annual payments	$ 452,000,000.0

Development Derivative Liability - Schedule of Development Derivative Liability (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance at fair market value	$ 257,868	$ 134,839
Amounts received under the SFJ Agreement and SFJ Amendment		20,000
Loss recorded in loss from remeasurement of development derivative liability	17,084	68,406
Balance at fair market value	$ 274,952	$ 223,245

Long-term Debt - Additional Information (Detail) $ / shares in Units, $ in Thousands				1 Months Ended	3 Months Ended
	Jan. 01, 2021 USD ($)	May 12, 2020 USD ($)	Sep. 16, 2019 USD ($)	Jan. 31, 2021 USD ($) shares	Mar. 31, 2021 USD ($) d $ / shares shares	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	May 06, 2020 CounterParty $ / shares	Sep. 11, 2019 USD ($) CounterParty $ / shares
Debt Instrument [Line Items]
Aggregate principal amount converted					$ 126,129
Loss on conversion of debt					39,487
Forfeiture of accrued interest in exchange of convertible notes					1,668
Amortization of debt discounts					$ 360
ASU 2020-06 [Member]
Debt Instrument [Line Items]
Change in accounting principle accounting standards update adopted					true
Change in accounting principle accounting standards update adoption date					Jan. 01, 2021
Increase (decrease) in net debt	$ 149,700
Decrease in net equity	149,700
Convertible notes	149,700
Non-cash interest expense	17,100
Amortization of debt issuance costs	1,100
Common Stock [Member]
Debt Instrument [Line Items]
Shares issued \| shares					3,976
2019 Convertible Notes [Member]
Debt Instrument [Line Items]
Premium paid for capped call transactions					$ 28,400
2019 Convertible Notes [Member] \| ASU 2020-06 [Member]
Debt Instrument [Line Items]
Debt issuance costs	2,400
Convertible notes	74,900
2020 Convertible Notes [Member]
Debt Instrument [Line Items]
Premium paid for capped call transactions					$ 43,100
2020 Convertible Notes [Member] \| ASU 2020-06 [Member]
Debt Instrument [Line Items]
Debt issuance costs	2,300
Convertible notes	$ 95,500
Capped Call Transactions [Member]
Debt Instrument [Line Items]
Number of counterparties \| CounterParty								2	2
Initial conversion price \| $ / shares								$ 39.4625	$ 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
Redemption period, start date					Sep. 20, 2023
Threshold percentage of stock price trigger					130.00%
Threshold trading days \| d					20
Threshold consecutive trading days \| d					30
Redemption price, percentage					100.00%
Amortization of debt issuance costs					$ 400	$ 100
Debt interest expense					4,200	3,900
Amortization of debt discounts						1,900
Accrued semi annual coupon payable					3,800	$ 1,900
Debt issuance costs gross					7,700
Long-term debt					$ 386,200		$ 358,800
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
Payment of convertible debt discounts and commissions			6,600
Payment of convertible debt offering expenses			500
Payments of transactions cost			28,400
Debt instrument effective interest rate									10.50%
Debt instrument convertible carrying amount of liability component									$ 145,100
Debt discount									74,900
Debt issuance costs									7,100
Convertible Senior Notes Due 2026 [Member] \| 2019 Convertible Notes [Member] \| Exchange Agreements [Member]
Debt Instrument [Line Items]
Conversion ratio				0.0253405
Debt issuance costs				$ 3,300
Increase (decrease) in net debt				(122,800)
Aggregate principal amount converted				$ 126,100	$ 126,100
Increase in shares outstanding \| shares				3,906,869
Shares issued \| shares				3,196,172
Additional shares issued \| shares				710,697
Additional shares issued for settlement of debt issuance cost paid \| shares				69,491
Loss on conversion of debt				$ 39,500
Loss on conversion of debt related to additional shares issued				36,400
Additional amount issued in payment of issuance costs				3,100
Forfeiture of accrued interest in exchange of convertible notes				$ 1,700
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
Convertible Senior Notes Due 2026 [Member] \| 2019 Convertible Notes [Member] \| Equity Component [Member]
Debt Instrument [Line Items]
Debt issuance costs									$ 2,400
Convertible Senior Notes Due 2026 [Member] \| 2020 Convertible Notes [Member]
Debt Instrument [Line Items]
Net proceeds from the sale of the notes		$ 322,900
Payment of convertible debt discounts and commissions		5,700
Payment of convertible debt offering expenses		300
Payments of transactions cost		$ 43,100
Debt instrument effective interest rate		10.50%
Debt instrument convertible carrying amount of liability component		$ 204,500
Debt discount		95,500
Debt issuance costs		6,000
Convertible Senior Notes Due 2026 [Member] \| 2020 Convertible Notes [Member] \| Liability Component [Member]
Debt Instrument [Line Items]
Debt issuance costs		3,700
Convertible Senior Notes Due 2026 [Member] \| 2020 Convertible Notes [Member] \| Equity Component [Member]
Debt Instrument [Line Items]
Debt issuance costs		2,300
Convertible Senior Notes Due 2026 [Member] \| Private Offering [Member] \| 2019 Convertible Notes [Member]
Debt Instrument [Line Items]
Principal amount			$ 220,000
Convertible Senior Notes Due 2026 [Member] \| Private Offering [Member] \| 2020 Convertible Notes [Member]
Debt Instrument [Line Items]
Principal amount		$ 300,000

Leases - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
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 of these 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	$ 1.3	$ 1.0
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 - Schedule of Additional Information Related to Operating Lease Assets and Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Operating Lease Assets	$ 22,518	$ 17,719
Operating Lease Liabilities	$ 23,811	$ 18,902
Weighted Average Remaining Term in years	5 years 4 months 6 days	4 years 7 months 28 days
Weighted Average discount rate used to measure outstanding lease liabilities	7.76%	7.74%

Leases - Supplemental Cash Flow Information Related to Operating Leases (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Operating cash flows for operating leases	$ 1,588	$ 968
Operating lease assets obtained in exchange for lease obligations	$ 5,675	$ 334

Leases - Maturities of Operating Lease Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Leases [Abstract]
2021	$ 4,204
2022	5,415
2023	5,480
2024	4,811
2025 and thereafter	9,267
Total future minimum lease payments less	29,177
Imputed interest	(5,366)
Operating Lease Liabilities	$ 23,811	$ 18,902

Marketable Securities - Schedule of Amortized Cost, Gross Unrealized Holding Losses and Fair Value of Available-for-Sale Debt Securities by Type of Security (Detail) - U.S. Government-Related Obligations [Member] - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Available for sale securities:
Amortized Cost	$ 458,158	$ 311,877
Gross Unrealized Holding Gains	79	11
Gross Unrealized Holding Losses		(19)
Fair Value	$ 458,237	$ 311,869

Other Comprehensive Income and Accumulated Other Comprehensive Income - Summary of Changes in Accumulated Other Comprehensive Income/(Loss), by Component (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ 204,557	$ 34,229
Net other comprehensive income (loss)	(1,503)	1,164
Ending balance	51,658	258,997
Unrealized Gains (Losses) from Marketable Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(8)
Net other comprehensive income (loss)	79	1,394
Ending balance	71	1,394
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(109)	(154)
Net other comprehensive income (loss)	(1,582)	(230)
Ending balance	(1,691)	(384)
Total Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(117)	(154)
Ending balance	$ (1,620)	$ 1,010

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669619-108580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 45
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118261656&loc=d3e32136-110900

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(21))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=121640130&loc=d3e1436-108581

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450520&loc=d3e32583-110901

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669625-108580

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(23))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(19))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

+ Details

- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

+ References + Details

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	Mar. 31, 2021	Dec. 31, 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 256,757	$ 471,092
Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	213,175	427,515
Bank Certificates of Deposit [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	43,582	43,577
Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	256,757	471,092
Level 1 [Member] \| Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	213,175	427,515
Level 1 [Member] \| Bank Certificates of Deposit [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 43,582	$ 43,577

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Level 1 [Member] \| Convertible Senior Notes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Convertible notes	$ 547.3
Convertible notes, interest rate	3.50%
Level 2 [Member] \| Convertible Senior Notes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Convertible notes		$ 676.2
Convertible notes, interest rate		3.50%
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Percentage of cost of borrowing	11.76%
Level 3 [Member] \| SFJ Agreement [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Percentage of cost of borrowing	8.00%

Fair Value Measurements - Schedule of Financial Instruments and the Related Fair Value Hierarchy of the Valuation Techniques Utilized (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 458,237	$ 401,859
Total Financial Liabilities	274,952	257,868
Cash and Cash Equivalents [Member] \| US Government Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets		89,990
Marketable Securities [Member] \| US Government Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	458,237	311,869
Development Derivative Liability [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	274,952	257,868
Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	458,237	401,859
Level 1 [Member] \| Cash and Cash Equivalents [Member] \| US Government Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets		89,990
Level 1 [Member] \| Marketable Securities [Member] \| US Government Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	458,237	311,869
Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	274,952	257,868
Level 3 [Member] \| Development Derivative Liability [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	$ 274,952	$ 257,868

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Tax Expense Benefit Continuing Operations [Abstract]
Minimum percentage of tax position likelihood of being realized upon examination by taxing authorities	50.00%
Unrecognized income tax benefits	$ 0
Current income tax expense or benefit	0	$ 0
Deferred income tax expense or benefit	$ 0	$ 0

License and Collaboration Agreements - Additional Information (Detail) - USD ($)			1 Months Ended	3 Months Ended	12 Months Ended
	Nov. 30, 2020	Oct. 27, 2020	Jan. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract research and development expense				$ 8,100,000
Contract research and development receivable					$ 43,000,000.0
Contract research and development current				20,000,000.0	25,000,000.0
Contract research and development long-term assets					18,000,000.0
Contract research and development other assets				6,100,000
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
Collaboration and License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development cost reimbursement					80,000,000.0
Collaboration and License Agreement [Member] \| License [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment					$ 250,000,000.0
Collaboration and License Agreement [Member] \| Swedish Orphan Biovitrum AB (Publ) [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment		250,000,000.0
Development cost reimbursement		$ 80,000,000.0
Royalties entitled to receive after first commercial sale of applicable licensed product period		10 years
Contract research and development reimbursement				80,000,000.0
Contract research and development receivable				26,100,000
Proceeds from contract research and development			$ 25,000,000.0
Collaboration and License Agreement [Member] \| Swedish Orphan Biovitrum AB (Publ) [Member] \| License [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue				$ 0
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 and commercial milestone events		915,000,000.0
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

License Agreements - Additional Information (Detail)	1 Months Ended	3 Months Ended	12 Months Ended
License Agreements - Additional Information (Detail)	Sep. 30, 2014 USD ($)	Mar. 31, 2021 USD ($) License	Dec. 31, 2020 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accrued expenses		$ 69,398,000	$ 111,935,000
Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments		$ 15,000,000.0
Payment of royalty fees		6.00%
Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of royalty fees		3.00%
University of Pennsylvania [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Annual maintenance fees	$ 100,000
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]
Royalty expense owed			25,000,000.0
Accrued expenses			25,000,000.0
License fees			$ 25,000,000.0

Commitments and Contingencies - Additional Information (Detail) - USD ($)		3 Months Ended
	Apr. 01, 2021	Mar. 31, 2021
Commitments And Contingencies [Line Items]
Estimated termination costs and other fees		$ 3,200,000
Incurred any cost to defend lawsuits or settle claims		0
Bachem [Member]
Commitments And Contingencies [Line Items]
Non-cancellable purchase commitments		16,400,000
Bachem [Member] \| Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Non-cancellable purchase commitments	$ 2,900,000
NOF [Member]
Commitments And Contingencies [Line Items]
Non-cancellable purchase commitments		$ 32,400,000
NOF [Member] \| Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Non-cancellable purchase commitments	$ 6,400,000

Net Loss per Share - Summary of Shares Outstanding that were Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	24,334	15,307
Convertible Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	9,981	5,575
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	13,404	9,434
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	949	298