0001564590-20-034763 | 10-Q | XBRL Viewer | Apellis Pharmaceuticals INC

Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2020	Jul. 27, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
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		75,603,991
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	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 317,348	$ 351,985
Marketable securities	515,476
Prepaid assets	17,925	19,802
Restricted cash	1,248
Other current assets	1,828	1,308
Total current assets	853,825	373,095
Non-current Assets:
Right-of-use assets	12,959	14,110
Property and equipment, net	2,416	1,655
Other assets	906	385
Total assets	870,106	389,245
Current liabilities:
Accounts payable	9,927	8,361
Accrued expenses	45,399	54,783
Current portion of right of use liabilities	2,664	2,609
Total current liabilities	57,990	65,753
Long-term liabilities:
Convertible senior notes	348,842	142,567
Development derivative liability	220,475	134,839
Operating lease liabilities	10,735	11,857
Total liabilities	638,042	355,016
Stockholders' equity:
Preferred stock, $0.0001 par value; 10.0 million shares authorized, and zero shares issued and outstanding at June 30, 2020 and December 31, 2019	0	0
Common stock, $0.0001 par value; 200.0 million shares authorized at June 30, 2020 and December 31, 2019; 75.6 million shares issued and outstanding at June 30, 2020, and 63.9 million shares issued and outstanding at December 31, 2019	8	6
Additional paid-in capital	1,100,639	615,850
Accumulated other comprehensive income/(loss)	329	(154)
Accumulated deficit	(868,912)	(581,473)
Total stockholders' equity	232,064	34,229
Total liabilities and stockholders' equity	$ 870,106	$ 389,245

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000.0	10,000,000.0
Preferred stock, issued	0	0
Preferred stock, outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000.0	200,000,000.0
Common stock, issued	75,600,000	63,900,000
Common stock, outstanding	75,600,000	63,900,000

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating expenses:
Research and development	$ 87,094	$ 50,698	$ 156,377	$ 91,178
General and administrative	28,414	12,778	57,918	20,949
Operating loss	(115,508)	(63,476)	(214,295)	(112,127)
Loss on extinguishment of debt				(1,208)
Gain/(loss) from remeasurement of development derivative liability	2,770	(9,104)	(65,636)	(9,840)
Interest income	1,025	1,421	3,300	2,288
Interest expense	(6,909)	(159)	(10,828)	(753)
Other income/(expense), net	5	228	20	(25)
Net loss	(118,617)	(71,090)	(287,439)	(121,665)
Other comprehensive gain/(loss):
Unrealized gain on marketable securities	(842)		552
Foreign currency gain/(loss)	161	(1)	(69)	1
Total other comprehensive gain/(loss)	(681)	(1)	483	1
Comprehensive loss, net of tax	$ (119,298)	$ (71,091)	$ (286,956)	$ (121,664)
Net loss per common share, basic and diluted	$ (1.57)	$ (1.12)	$ (3.85)	$ (2.01)
Weighted-average number of common shares used in net loss per common share, basic and diluted	75,550	63,264	74,635	60,581

Condensed Consolidated Statements of Changes in Stockholder's Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2018	$ 160,972	$ 5	$ 437,856	$ (123)	$ (276,766)
Beginning balance, Shares at Dec. 31, 2018		56,279
Issuance of common stock in follow-on offering, net of offering costs	109,604	$ 1	109,603
Issuance of common stock in follow-on offering, shares		6,900
Issuance of common stock upon exercise of stock options	192		192
Issuance of common stock upon exercise of stock options, shares		39
Share-based compensation expense	4,559		4,559
Net loss	(50,574)				(50,574)
Foreign currency gain (loss)	2			2
Ending balance at Mar. 31, 2019	224,755	$ 6	552,210	(121)	(327,340)
Ending balance, Shares at Mar. 31, 2019		63,218
Beginning balance at Dec. 31, 2018	160,972	$ 5	437,856	(123)	(276,766)
Beginning balance, Shares at Dec. 31, 2018		56,279
Net loss	(121,665)
Foreign currency gain (loss)	1
Ending balance at Jun. 30, 2019	159,086	$ 6	557,632	(122)	(398,430)
Ending balance, Shares at Jun. 30, 2019		63,672
Beginning balance at Mar. 31, 2019	224,755	$ 6	552,210	(121)	(327,340)
Beginning balance, Shares at Mar. 31, 2019		63,218
Deferred issuance costs	(23)		(23)
Issuance of common stock upon exercise of stock options	1,262		1,262
Issuance of common stock upon exercise of stock options, shares		454
Share-based compensation expense	4,183		4,183
Net loss	(71,090)				(71,090)
Foreign currency gain (loss)	(1)			(1)
Ending balance at Jun. 30, 2019	159,086	$ 6	557,632	(122)	(398,430)
Ending balance, Shares at Jun. 30, 2019		63,672
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 (loss) on available-for-sale investments	1,394			1,394
Net loss	(168,822)				(168,822)
Foreign currency gain (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, 2019	34,229	$ 6	615,850	(154)	(581,473)
Beginning balance, Shares at Dec. 31, 2019		63,938
Unrealized gain (loss) on available-for-sale investments	552
Net loss	(287,439)
Foreign currency gain (loss)	(69)
Ending balance at Jun. 30, 2020	232,064	$ 8	1,100,639	329	(868,912)
Ending balance, Shares at Jun. 30, 2020		75,590
Beginning balance at Mar. 31, 2020	258,997	$ 7	1,008,275	1,010	(750,295)
Beginning balance, Shares at Mar. 31, 2020		75,422
Deferred issuance costs	(35)		(35)
Issuance of common stock upon exercise of stock options	1,355	$ 1	1,354
Issuance of common stock upon exercise of stock options, shares		148
Share-based compensation expense	11,489		11,489
Unrealized gain (loss) on available-for-sale investments	(842)			(842)
Recognition of debt discount on convertible notes	122,147		122,147
Purchase of capped call transactions and associated costs	(43,112)		(43,112)
Issuance of common stock to employee stock purchase plan	521		521
Issuance of common stock to employee stock purchase plan, shares		20
Net loss	(118,617)				(118,617)
Foreign currency gain (loss)	161			161
Ending balance at Jun. 30, 2020	$ 232,064	$ 8	$ 1,100,639	$ 329	$ (868,912)
Ending balance, Shares at Jun. 30, 2020		75,590

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating Activities
Net loss	$ (287,439)	$ (121,665)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	20,783	8,742
Loss on early extinguishment of debt		1,208
Loss from remeasurement of development derivative liability	65,636	9,840
Amortization of right-of-use assets	84	149
Depreciation expense	180	87
Amortization of debt discounts		38
Amortization of term loan facility discounts		104
Amortization of discounts for convertible notes, net of financing costs	5,548
Changes in operating assets and liabilities:
Prepaid assets	1,877	10,357
Other current assets	(824)	(3,527)
Other assets	(518)	(91)
Accounts payable	1,600	3,801
Accrued expenses	(9,570)	15,399
Other liabilities		91
Net cash used in operating activities	(202,643)	(75,467)
Investing Activities
Purchase of property and equipment	(973)	(1,067)
Purchase of available-for-sale securities	(567,188)
Proceeds from maturity of available-for-sale securities	52,500
Net cash used in investing activities	(515,661)	(1,067)
Financing Activities
Proceeds from issuance of common stock, net of issuance costs	381,423	109,629
Proceeds from development derivative liability	20,000	100,000
Payments for capped call transactions and associated costs	(43,112)
Proceeds from issuance of convertible notes, net of issuance costs	323,074
Proceeds from exercise of stock options	3,029	1,454
Proceeds from issuance of common stock under employee share purchase plan	521
Repayment of term loan facility		(21,701)
Net cash provided by financing activities	684,935	189,382
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(20)	12
Net increase in cash, cash equivalents and restricted cash	(33,389)	112,860
Cash, cash equivalents and restricted cash at beginning of period	351,985	176,268
Cash, cash equivalents and restricted cash at end of period	318,596	289,128
Reconciliation of cash, cash equivalents and restricted cash to the consolidated balance sheets:
Cash and cash equivalents	317,348	289,128
Restricted cash	1,248
Cash, cash equivalents and restricted cash at end of period	318,596	289,128
Supplemental Disclosure of Financing Activities
Cash paid for Interest	$ 3,829	$ 728

Nature of Organization and Operations

6 Months Ended

Jun. 30, 2020

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.

Convertible Notes Offering

On May 12, 2020, the Company completed a private offering of $300.0 million aggregate principal amount of 3.5% convertible senior notes due 2026 (the “2020 Convertible Notes”). The aggregate purchase price of the 2020 Convertible Notes was $328.9 million, which amount includes accrued interest from March 15, 2020 to, but not including, May 12, 2020.

The net proceeds from the sale of the 2020 Convertible Notes were approximately $322.9 million after deducting the initial purchasers’ discounts and commissions and offering expenses payable by the Company. The Company used $43.1 million of the net proceeds from the offering to pay the cost of the capped call transactions described below.

The 2020 Convertible Notes form a single series with, and have the same terms as, the Company’s $220.0 million aggregate principal amount of 3.500% convertible senior notes due 2026 issued on September 16, 2019, (the “2019 Convertible Notes”, and together with the 2020 Convertible Notes, the “Convertible Notes”), but have a different issue date, issue price, CUSIP number and different restrictions on transfer. The 2020 Convertible Notes were issued as additional notes under the indenture (the “Indenture”), dated as of September 16, 2019, by and between the Company and U.S. Bank National Association, as trustee (the “Trustee”), under which the 2019 Convertible Notes were issued. The 2020 Convertible Notes rank equal in right of payment to the 2019 Convertible Notes.

The 2020 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 earlier converted, redeemed or repurchased in accordance with their terms. See Note 5 – Long-term Debt for additional information.

Capped Call Transactions

On May 6, 2020, concurrently with the pricing of the 2020 Convertible Notes, the Company entered into capped call transactions with two counterparties. The capped call transactions are expected generally to reduce the potential dilution to the Company’s common stock upon any conversion of the 2020 Convertible Notes and/or offset any cash payments the Company is required to make in excess of the principal amount of converted 2020 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 2020 Convertible Notes) and is subject to anti-dilution adjustments substantially similar to those applicable to the conversion rate of such 2020 Convertible Notes.

Follow-on Public Offerings

On January 13, 2020, the Company issued and sold 10,925,000 shares of its common stock at a price per share to the public of $37.00 in a follow-on public offering including an additional 1,425,000 shares of its common stock that were sold at the follow-on public offering price of $37.00 per share pursuant to the underwriters’ in full exercise of their option to purchase additional shares of common stock. The Company received net proceeds of $381.5 million after deducting underwriting discounts and commissions of $22.2 million and offering costs of $0.5 million for these transactions.

Liquidity and Financial Condition

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 July 30, 2020, the date of issuance of these unaudited condensed consolidated financial statements, the Company believes that its cash and cash equivalents of $317.3 million and marketable securities of $515.5 million as of June 30, 2020 will be sufficient to fund its operations and capital expenditure requirements for at least the next twelve months from the date of issuance of the unaudited interim 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. Management’s plans in order 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 on a timely basis on terms that are favorable to the Company or at all, 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

6 Months Ended

Jun. 30, 2020

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 Ireland Ltd, Apellis Switzerland GmbH 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 balance sheet as of December 31, 2019 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 six months ended June 30, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 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, 2019 included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission on February 27, 2020.

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, the Australian research and development credit, accounts payable and accrued liabilities. Management believes that the carrying amounts of certain cash and cash equivalents, the Australian research and development credit, accounts payable and accrued expenses approximate the fair value due to the short-term nature of those instruments.

Cash and Cash Equivalents

Cash and cash equivalents are defined as cash in banks and investment instruments having maturities of three months or less from their acquisition date. The carrying amounts reported in the consolidated balance sheets for 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 $1.2 million as of June 30, 2020. The Company records as restricted cash the collateral used to secure these letters of credit. The Company did not have restricted cash as of December 31, 2019.

Foreign Currency

The financial position and results of operations of the Company's Australian, Swiss and Irish 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.

Accrued Expenses

6 Months Ended

Jun. 30, 2020

Text Block [Abstract]

Accrued Expenses

3. Accrued Expenses

Accrued expenses are as follows:

	June 30,		December 31,
	2020		2019
Accrued research and development	$	23,815	$	36,449
Accrued payroll liabilities		11,598		11,443
Other		9,986		6,891
Total	$	45,399	$	54,783

Development Derivative Liability

6 Months Ended

Jun. 30, 2020

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

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. This additional $20.0 million payment is in addition to and not part of the Additional SFJ Funding.

In the six months ended June 30, 2020 and the year ended December 31,2019, the Company received $20.0 million and $100.0 million, respectively, from SFJ, as the Company met milestones as identified in the SFJ Agreement.

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. Such payments will be proportionately adjusted in the event that the actual funding from SFJ is greater than $120.0 million (including as a result of the payment of the Additional SFJ Funding but excluding the $20.0 million funding payment made under the SFJ Amendment). 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 balance sheet and is considered a level three derivative, and as such is remeasured each quarter. During the three months ended June 30, 2019, the Company received $40.0 million under the SFJ Agreement. The change in fair value due to the remeasurement of the development derivative liability resulted in a $2.8 million gain and $9.1 million loss, for the three months ended June 30, 2020 and 2019, respectively, recorded on the condensed consolidated statement of operations. During the six months ended June 30, 2020 and 2019, the Company received $20.0 million and $100.0 million, respectively. The change in fair value of the development derivative liability included in the statement of operations for the six months ended June 30, 2020 and 2019 was a loss of $65.6 million and $9.8 million, respectively. The development derivative liability has a remeasured fair value of $220.5 million on the consolidated balance sheet at June 30,2020.

The following table presents a rollforward of the development derivative liability:

	Six Months Ended June 30,
	2020			2019
Balance at fair market value, January 1,	$	134,839		$	—
Amounts received under the SFJ agreement and SFJ amendment		20,000			60,000
Loss recorded in loss from remeasurement of development derivative liability		68,406			736
Balance at fair market value, March 31,	$	223,245		$	60,736
Amounts received under the SFJ agreement and SFJ amendment		—			40,000
Gain/(loss) recorded in loss from remeasurement of development derivative liability		(2,770	)		9,104
Balance at fair market value, June 30,	$	220,475		$	109,840

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 (15.08%).

SFJ’s implied cost of borrowing was 8.0% and the Company’s implied cost of borrowing was 15.08% 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

6 Months Ended

Jun. 30, 2020

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 which were issued pursuant to 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 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 $39.46 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.

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.

Interest expense for the Convertible Notes was $ $6.9 million and $10.8 million and for the three and six months ended June 30, 2020, respectively. For the three months ended June 30, 2020, interest expense included the amortization of the discount on the Convertible Notes of $3.4 million, accrued semi-annual coupon payable of $3.4 million and amortization of debt issuance costs of $0.1 million. For the six months ended June 30, 2020 interest expense included the amortization of the discount on the Convertible Notes of $5.3 million, accrued semi-annual coupon payable of $5.3 million and amortization of debt issuance costs of $0.2 million. As of June 30, 2020, $8.1 million of debt issuance costs was recorded on the consolidated balance sheet as a reduction to the carrying amount of the Convertible Notes.

The aggregate balance of the Convertible Notes, net of unamortized debt issuance costs, as of June 30, 2020 and December 31, 2019 was $348.8 million and $142.6 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 as June 30, 2020 for the 2019 and 2020 Convertible notes, respectively.

Term Loan Facility

On October 20, 2017, the Company entered into a loan and security agreement with Silicon Valley Bank (“SVB”) to provide for a $20.0 million term loan facility (the “term loan facility”). Borrowings under the term loan facility accrued interest at a floating rate per annum equal to the WSJ prime rate plus 1.50%. Under the agreement, the Company was required to make monthly interest-only payments through November 1, 2019 and was required to make 24 equal monthly payments of principal, plus accrued interest, from November 1, 2019 through October 1, 2021, when all unpaid principal and interest became due and payable.

On March 26, 2019, the Company voluntarily repaid all outstanding amounts due and owed, including applicable termination fees, under the term loan facility. The final payment of $21.8 million totaled per diem interest of $0.1 million and $21.7 million for the outstanding balance of the term loan which included (i) a final payment equal to 8% of the original principal amount of the term loan of $1.6 million, and (ii) a prepayment fee contractually owed of $0.1 million plus other fees which resulted in a total loss on extinguishment of debt of $1.2 million.

In connection with the Company’s entry into the term loan facility, the Company issued to SVB a warrant to purchase 14,064 shares of the Company’s common stock with an exercise price per share of $5.484. The warrant has a ten-year term and included a put option pursuant to which, in the event of an acquisition, change in control or dissolution or winding up of the Company, or the expiration of the warrant, SVB could have required the Company to repurchase the warrant for a total aggregate purchase price of $250 thousand. The warrants were exercised in November 2019.

Promissory Note

On October 19, 2017, the Company issued and sold an unsecured promissory note in the principal amount of $7.0 million to Golda Darty Partners S.A. (“GDP”). The promissory note accrued interest at a rate per annum of 8.0%, and was due and payable quarterly in arrears on the 19th day of each April, July, October and January. The promissory note had a maturity date of

October 19, 2022 when the $7.0 million would be due and payable in its entirety. The promissory note was contractually subordinated to the Company’s obligations to SFJ under the SFJ Agreement.

On September 16, 2019, the Company voluntarily repaid all outstanding amounts due and owed under the promissory note, except for a small amount of interest subsequently repaid. The payment of $7.1 million totaled per diem interest of $0.1 million and $7.0 million for the outstanding principal balance of the promissory note.

In connection with the issuance and sale of the above promissory note, the Company issued to GDP a warrant to purchase 93,764 shares of the Company’s common stock at a price per share of $5.484, which was exercised in whole in October 2017. The Company recorded the fair value of the warrant in the aggregate amount of $0.4 million as a discount to the promissory note. This amount was being accreted as additional interest expense over the term of the promissory note. Upon the repayment of the promissory note, the Company recorded a loss on extinguishment of debt of $0.3 million due to the remaining discount.

The contractual maturities of the Company’s long-term debt obligations due subsequent to June 30, 2020 consist of the $348.8 million Convertible Senior Notes which mature in September 2026.

Leases

6 Months Ended

Jun. 30, 2020

Leases [Abstract]

Leases

6. Leases

On January 1, 2019, the Company adopted ASU 2016-02 Leases (Topic 842) using a modified retrospective method. The Company recognized $5.5 million of lease assets and liabilities. There was no impact to retained earnings upon adoption of Topic 842. 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. During 2019, the Company leased additional office space resulting in an initial recognition value of $9.8 million of lease assets and liabilities.

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 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 June 30, 2020 and December 31, 2019, all leases were classified as operating lease assets and liabilities. Additional information related to the operating lease assets and liabilities is as follows:

	June 30,			December 31,
	2020			2019
Operating Lease Assets	$	12,959		$	14,110
Operating Lease Liabilities	$	13,399		$	14,466
Weighted Average Remaining Term in years		4.57		5.01
Weighted Average discount rate used to measure outstanding lease liabilities		8.30	%		8.19	%

For the three months ended June 30, 2020 and 2019, the total lease cost for operating lease expense was $1.0 million and $0.5 million, respectively. For the six months ended June 30, 2020 and 2019, the total lease cost for operating lease expense was $2.0 million and $0.9 million.

Supplemental cash flow information related to operating leases for the six months ended June 30 is as follows:

	2020		2019
Operating cash flows for operating leases	$	2,056	$	713
Operating lease assets obtained in exchange for lease obligations	$	334	$	7,287

The maturities of the Company’s operating lease liabilities as of June 30, 2020 are as follows:

2020	$	1,872
2021		3,519
2022		3,283
2023		3,288
2024 and thereafter		4,107
Total future minimum lease payments less		16,069
Imputed interest		(2,670	)
Total operating lease liabilities	$	13,399

Marketable Securities

6 Months Ended

Jun. 30, 2020

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 June 30, 2020 were as follows:

	As of June 30, 2020
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses		Fair Value
U.S. Government-related obligations	$	514,924	$	555	$	3	$	515,476

All available-for-sale securities mature in one year or less. The Company did not hold available-for-sale securities as of December 31, 2019.

Other Comprehensive Income and Accumulated Other Comprehensive Income

6 Months Ended

Jun. 30, 2020

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 and six months ended June 30, 2020 and 2019:

	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
Net other comprehensive income (loss)		(842	)		161			(681	)
Balances, June 30, 2020	$	552		$	(223	)	$	329

	Unrealized Gains (Losses) from Marketable Securities		Foreign Currency Translation Adjustment			Total Accumulated Other Comprehensive Income (Loss)
Balances, December 31, 2018	$	—	$	(123	)	$	(123	)
Net other comprehensive income (loss)		—		2			2
Balances, March 31, 2019	$	—	$	(121	)	$	(121	)
Net other comprehensive income (loss)		—		(1	)		(1	)
Balances, June 30, 2019	$	—	$	(122	)	$	(122	)

Fair Value Measurements

6 Months Ended

Jun. 30, 2020

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:

		June 30, 2020
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents:	Money market funds	$	273,452	$	—	$	—	$	273,452
	Bank certificates of deposit		40,816		—		—		40,816
Total Financial Assets		$	314,268	$	—	$	—	$	314,268

Financial Liabilities:
Convertible senior notes	Convertible senior notes*	$	—	$	—	$	378,732	$	378,732
Total Financial Liabilities		$	—	$	—	$	378,732	$	378,732

		December 31, 2019
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents	Money market funds	$	281,314	$	—	$	—	$	281,314
Total Financial Assets		$	281,314	$	—	$	—	$	281,314

Financial Liabilities:
Convertible senior notes	Convertible senior notes*	$	—	$	—	$	149,496	$	149,496
Total Financial Liabilities		$	—	$	—	$	149,496	$	149,496

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

The fair value of debt component of the Company's Convertible Notes was $378.7 million and $149.5 million, as of June 30, 2020 and December 31, 2019, respectively, based on the discounted cash flows for comparable straight debt instrument. 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 June 30, 2020 and December 31, 2019.

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

		June 30, 2020
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Marketable Securities:	US government obligations	$	495,494	$	—	$	—	$	495,494
	US government agency		19,982		—		—		19,982
Total Financial Assets		$	515,476	$	—	$	—	$	515,476

Financial Liabilities:
Development derivative liability	Development derivative liability	$	—	$	—	$	220,475	$	220,475
Total Financial Liabilities		$	—	$	—	$	220,475	$	220,475

		December 31, 2019
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Liabilities:
Development derivative liability	Development derivative liability	$	—	$	—	$	134,839	$	134,839
Total Financial Liabilities		$	—	$	—	$	134,839	$	134,839

The fair value of the SFJ Agreement is presented as a 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 (15.08%).

- 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

Refundable Research and Development Credit and Income Taxes

6 Months Ended

Jun. 30, 2020

Refundable Research And Development Credit And Income Taxes [Abstract]

Refundable Research And Development Credit And Income Taxes

10. Refundable Research and Development Credit and Income Taxes

The Company earns non-income related refundable Australian research and development credits that are settled and paid to the Company annually. The associated income from the credits are an offset to research and development expenses.

The Company’s income tax provision is computed based on the federal statutory rate and the average state statutory rates, net of the related federal benefit. For the three and six months ended June 2020 and 2019, there were no current or deferred income tax expenses or benefits due to the Company’s net losses, research and development credits and increases in its deferred tax asset valuation allowance during those periods.

The Company’s estimate of the realizability of the deferred tax asset is dependent on estimates of projected future levels of taxable income. In analyzing future taxable income levels, the Company considered all evidence currently available, both positive and negative. Based on this analysis, the Company has recorded a valuation allowance for all deferred tax assets as of June 30, 2020.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

11. Commitments and Contingencies

The Company has entered into a leasing agreement for lab space in Watertown, Massachusetts with an estimated commencement date of August 6, 2020 (the “Lab Lease”). The Lab Lease has a term of 85 months and includes leasing 9,704 square feet of office space. The Lab Lease provides for initial monthly lease payments of $60 thousand per month. The base rent payable over the lease period is $5.4 million.

The Company has entered into a new lease for its Switzerland office, with a commencement date of July 1, 2020 (the “Swiss Office Lease”). The Swiss Office Lease has a term of 60 months with and includes leasing 938 square meters of office space. The

Swiss Office Lease provides for initial monthly lease payments of CHF38 thousand per month. The base rent payable over the initial lease period is CHF2.3 million.

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. 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 June 30, 2020, the Company would be required to pay certain termination costs and other fees of approximately $1.8 million that would be incurred in future periods.

As of June 30, 2020, the Company has non-cancellable purchase commitments for 2020 with certain manufacturing vendors in the amount of approximately $14.1 million.

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.

Net Loss per Share

6 Months Ended

Jun. 30, 2020

Earnings Per Share [Abstract]

Net Loss per Share

12. 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:

	For the Three Months Ended June 30,				For the Six Months Ended June 30,
	2020		2019		2020		2019
Convertible notes		13,177		—		13,177		—
Common stock options		11,832		9,095		11,832		9,095
Restricted stock units		349				349		—
Common stock warrants		—		14		—		14
Total		25,358		9,109		25,358		9,109

Related Party Transaction

6 Months Ended

Jun. 30, 2020

Related Party Transaction

13. Related Party Transaction

Effective as of May 1, 2018, the Company entered into a subscription license agreement and a services agreement with Revon Systems, Inc. (“Revon”). Under the subscription license agreement, Revon granted the Company an exclusive license to use the Revon software platform and applications for any purpose with respect to the Company's programs in age-related macular degeneration, hemolytic diseases and complement-dependent nephropathies for an annual license fee of $0.2 million for a two year initial term and an option to obtain a perpetual, exclusive license thereafter for $0.4 million. Under the services agreement, Revon provided development services with respect to the Revon software to the Company for $0.3 million during the first year. Prior to the acquisition of Revon by an unrelated third party in July 2019, the Company paid the remainder of the annual license fee due for the second year, exercised the option for the perpetual license and discontinued the services agreement.

Each of Cedric Francois, the Company’s chief executive officer, Pascal Deschatelets, the Company’s chief scientific officer, and Alec Machiels, a member of the board of directors, was an affiliate of Revon. The Board approved the Revon agreements after review by a subcommittee of the disinterested members of the Board and determination by the full Board that the terms of the Revon agreements were fair, reasonable and in the best interests of the Company. The exercise of the option for the perpetual license was approved in accordance with the Company’s related party transaction policy.

Basis of Presentation (Policies)	6 Months Ended
Basis of Presentation (Policies)	Jun. 30, 2020
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 Ireland Ltd, Apellis Switzerland GmbH 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 balance sheet as of December 31, 2019 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 six months ended June 30, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 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, 2019 included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission on February 27, 2020.
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, the Australian research and development credit, accounts payable and accrued liabilities. Management believes that the carrying amounts of certain cash and cash equivalents, the Australian research and development credit, accounts payable and accrued expenses approximate the fair value due to the short-term nature of those instruments.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents are defined as cash in banks and investment instruments having maturities of three months or less from their acquisition date. The carrying amounts reported in the consolidated balance sheets for 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 $1.2 million as of June 30, 2020. The Company records as restricted cash the collateral used to secure these letters of credit. The Company did not have restricted cash as of December 31, 2019.
Foreign Currency	Foreign Currency The financial position and results of operations of the Company's Australian, Swiss and Irish 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.

Accrued Expenses (Tables)

6 Months Ended

Jun. 30, 2020

Text Block [Abstract]

Schedule of Accrued Expenses

Accrued expenses are as follows:

	June 30,		December 31,
	2020		2019
Accrued research and development	$	23,815	$	36,449
Accrued payroll liabilities		11,598		11,443
Other		9,986		6,891
Total	$	45,399	$	54,783

Development Derivative Liability (Tables)

6 Months Ended

Jun. 30, 2020

Research And Development [Abstract]

Schedule of Development Derivative Liability

The following table presents a rollforward of the development derivative liability:

	Six Months Ended June 30,
	2020			2019
Balance at fair market value, January 1,	$	134,839		$	—
Amounts received under the SFJ agreement and SFJ amendment		20,000			60,000
Loss recorded in loss from remeasurement of development derivative liability		68,406			736
Balance at fair market value, March 31,	$	223,245		$	60,736
Amounts received under the SFJ agreement and SFJ amendment		—			40,000
Gain/(loss) recorded in loss from remeasurement of development derivative liability		(2,770	)		9,104
Balance at fair market value, June 30,	$	220,475		$	109,840

Leases (Tables)

6 Months Ended

Jun. 30, 2020

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:

	June 30,			December 31,
	2020			2019
Operating Lease Assets	$	12,959		$	14,110
Operating Lease Liabilities	$	13,399		$	14,466
Weighted Average Remaining Term in years		4.57		5.01
Weighted Average discount rate used to measure outstanding lease liabilities		8.30	%		8.19	%

Supplemental Cash Flow Information Related to Operating Leases

Supplemental cash flow information related to operating leases for the six months ended June 30 is as follows:

	2020		2019
Operating cash flows for operating leases	$	2,056	$	713
Operating lease assets obtained in exchange for lease obligations	$	334	$	7,287

Maturities of Operating Lease Liabilities

The maturities of the Company’s operating lease liabilities as of June 30, 2020 are as follows:

2020	$	1,872
2021		3,519
2022		3,283
2023		3,288
2024 and thereafter		4,107
Total future minimum lease payments less		16,069
Imputed interest		(2,670	)
Total operating lease liabilities	$	13,399

Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2020

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 June 30, 2020 were as follows:

	As of June 30, 2020
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses		Fair Value
U.S. Government-related obligations	$	514,924	$	555	$	3	$	515,476

Other Comprehensive Income and Accumulated Other Comprehensive Income (Tables)

6 Months Ended

Jun. 30, 2020

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 and six months ended June 30, 2020 and 2019:

	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
Net other comprehensive income (loss)		(842	)		161			(681	)
Balances, June 30, 2020	$	552		$	(223	)	$	329

	Unrealized Gains (Losses) from Marketable Securities		Foreign Currency Translation Adjustment			Total Accumulated Other Comprehensive Income (Loss)
Balances, December 31, 2018	$	—	$	(123	)	$	(123	)
Net other comprehensive income (loss)		—		2			2
Balances, March 31, 2019	$	—	$	(121	)	$	(121	)
Net other comprehensive income (loss)		—		(1	)		(1	)
Balances, June 30, 2019	$	—	$	(122	)	$	(122	)

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2020

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:

		June 30, 2020
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents:	Money market funds	$	273,452	$	—	$	—	$	273,452
	Bank certificates of deposit		40,816		—		—		40,816
Total Financial Assets		$	314,268	$	—	$	—	$	314,268

Financial Liabilities:
Convertible senior notes	Convertible senior notes*	$	—	$	—	$	378,732	$	378,732
Total Financial Liabilities		$	—	$	—	$	378,732	$	378,732

		December 31, 2019
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Cash and cash equivalents	Money market funds	$	281,314	$	—	$	—	$	281,314
Total Financial Assets		$	281,314	$	—	$	—	$	281,314

Financial Liabilities:
Convertible senior notes	Convertible senior notes*	$	—	$	—	$	149,496	$	149,496
Total Financial Liabilities		$	—	$	—	$	149,496	$	149,496

* 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:

		June 30, 2020
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Assets:
Marketable Securities:	US government obligations	$	495,494	$	—	$	—	$	495,494
	US government agency		19,982		—		—		19,982
Total Financial Assets		$	515,476	$	—	$	—	$	515,476

Financial Liabilities:
Development derivative liability	Development derivative liability	$	—	$	—	$	220,475	$	220,475
Total Financial Liabilities		$	—	$	—	$	220,475	$	220,475

		December 31, 2019
Balance Sheet Classification	Type of Instrument	Level 1		Level 2		Level 3		Total
Financial Liabilities:
Development derivative liability	Development derivative liability	$	—	$	—	$	134,839	$	134,839
Total Financial Liabilities		$	—	$	—	$	134,839	$	134,839

Net Loss per Share (Tables)

6 Months Ended

Jun. 30, 2020

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:

	For the Three Months Ended June 30,				For the Six Months Ended June 30,
	2020		2019		2020		2019
Convertible notes		13,177		—		13,177		—
Common stock options		11,832		9,095		11,832		9,095
Restricted stock units		349				349		—
Common stock warrants		—		14		—		14
Total		25,358		9,109		25,358		9,109

Nature of Organization and Operations - Additional Information (Detail) $ / shares in Units, $ in Thousands				6 Months Ended
	May 12, 2020 USD ($)	Jan. 13, 2020 USD ($) $ / shares shares	Sep. 16, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	May 06, 2020 CounterParty $ / shares	Dec. 31, 2019 USD ($)	Sep. 11, 2019 CounterParty $ / shares
Nature Of Organization And Operations [Line Items]
Proceeds from follow-on public offering after deducting underwriting discounts and commissions				$ 381,423	$ 109,629
Cash and cash equivalents				317,348	$ 289,128		$ 351,985
Marketable securities				$ 515,476
Capped Call Transactions [Member]
Nature Of Organization And Operations [Line Items]
Number of counterparties \| CounterParty						2		2
Initial conversion price \| $ / shares						$ 39.4625		$ 39.4625
Follow-on Public Offerings [Member]
Nature Of Organization And Operations [Line Items]
Issuance of common stock in follow-on offering, shares \| shares		10,925,000
Price of common stock \| $ / shares		$ 37.00
Proceeds from follow-on public offering after deducting underwriting discounts and commissions		$ 381,500
Underwriting discounts and commissions		22,200
Offering Cost		$ 500
Over Allotment Option [Member]
Nature Of Organization And Operations [Line Items]
Issuance of common stock in follow-on offering, shares \| shares		1,425,000
Price of common stock \| $ / shares		$ 37.00
Convertible Senior Notes Due 2026 [Member]
Nature Of Organization And Operations [Line Items]
Debt instrument, stated percentage	3.50%
Debt instrument, due and payment description				The 2020 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
Convertible Senior Notes Due 2026 [Member] \| 2020 Convertible Notes [Member]
Nature Of Organization And Operations [Line Items]
Debt instrument, stated percentage	3.50%
Purchase price of convertible notes	$ 328,900
Net proceeds from the sale of the notes	322,900
Payments of transactions cost	43,100
Convertible Senior Notes Due 2026 [Member] \| Private Offering [Member] \| 2020 Convertible Notes [Member]
Nature Of Organization And Operations [Line Items]
Principal amount	300,000
Convertible Senior Notes Due 2026 [Member]
Nature Of Organization And Operations [Line Items]
Principal amount				$ 348,800
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
Convertible Senior Notes Due 2026 [Member] \| 2020 Convertible Notes [Member]
Nature Of Organization And Operations [Line Items]
Net proceeds from the sale of the notes	322,900
Payments of transactions cost	43,100
Convertible Senior Notes Due 2026 [Member] \| 2019 Convertible Notes [Member]
Nature Of Organization And Operations [Line Items]
Debt instrument, stated percentage			3.50%
Net proceeds from the sale of the notes			$ 212,900
Payments of transactions cost			28,400
Convertible Senior Notes Due 2026 [Member] \| Private Offering [Member] \| 2020 Convertible Notes [Member]
Nature Of Organization And Operations [Line Items]
Principal amount	$ 300,000
Convertible Senior Notes Due 2026 [Member] \| Private Offering [Member] \| 2019 Convertible Notes [Member]
Nature Of Organization And Operations [Line Items]
Principal amount			$ 220,000

Basis of Presentation - Additional Information (Detail) $ in Thousands	Jun. 30, 2020 USD ($)
Accounting Policies [Abstract]
Restricted cash	$ 1,248

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accrued Liabilities Current [Abstract]
Accrued research and development	$ 23,815	$ 36,449
Accrued payroll liabilities	11,598	11,443
Other	9,986	6,891
Total	$ 45,399	$ 54,783

Development Derivative Liability - Additional Information (Detail)		3 Months Ended				6 Months Ended		12 Months Ended
	Feb. 28, 2019 USD ($) Installment	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Jun. 07, 2019 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Minimum payment of additional funding amount			$ 20,000,000	$ 40,000,000	$ 60,000,000
Gain/(loss) from remeasurement of development derivative liability		$ 2,770,000	(68,406,000)	(9,104,000)	(736,000)	$ (65,636,000)	$ (9,840,000)
Development derivative liability		220,475,000	$ 223,245,000	109,840,000	$ 60,736,000	$ 220,475,000	109,840,000	$ 134,839,000
Level 3 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Implied cost of borrowing discount rates						15.08%
SFJ Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from SFJ agreement	$ 60,000,000.0					$ 20,000,000.0	100,000,000.0	$ 100,000,000.0
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
Minimum payment of additional funding amount	$ 120,000,000.0
Increase in additional funding amount under amendment									$ 20,000,000.0
Gain/(loss) from remeasurement of development derivative liability		2,800,000		(9,100,000)		(65,600,000)	$ (9,800,000)
Proceeds from collaborators of milestones				$ 40,000,000.0
Development derivative liability		$ 220,500,000				$ 220,500,000
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				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance at fair market value	$ 223,245	$ 134,839	$ 60,736		$ 134,839
Amounts received under the SFJ agreement and SFJ amendment		20,000	40,000	$ 60,000
Gain/(loss) recorded in loss from remeasurement of development derivative liability	(2,770)	68,406	9,104	736	65,636	$ 9,840
Balance at fair market value	$ 220,475	$ 223,245	$ 109,840	$ 60,736	$ 220,475	$ 109,840

Long-term Debt - Additional Information (Detail) $ / shares in Units, $ in Thousands						3 Months Ended	6 Months Ended
	May 12, 2020 USD ($)	Sep. 16, 2019 USD ($)	Mar. 26, 2019 USD ($)	Oct. 20, 2017 USD ($) Installment $ / shares shares	Oct. 19, 2017 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($) d $ / shares	Jun. 30, 2019 USD ($)	May 06, 2020 CounterParty $ / shares	Dec. 31, 2019 USD ($)	Sep. 11, 2019 USD ($) CounterParty $ / shares
Debt Instrument [Line Items]
Amortization of debt discounts								$ 38
Loss on extinguishment of debt								$ 1,208
Term Loan Facility [Member]
Debt Instrument [Line Items]
Principal amount			$ 21,700
Final payment due amount			21,800
Debt instrument per diem interest amount			$ 100
Final payment percentage equal to original principal amount			8.00%
Final payment towards original principal amount			$ 1,600
Prepayment fee			100
Loss on extinguishment of debt			$ 1,200
Silicon Valley Bank [Member] \| Term Loan Facility [Member]
Debt Instrument [Line Items]
Warrant to purchase common stock \| shares				14,064,000
Exercise price per share \| $ / shares				$ 5.484
Warrant term				10 years
Aggregate purchase price				$ 250
Loan and Security Agreement [Member] \| Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Debt instrument, due and payment description							the Company was required to make monthly interest-only payments through November 1, 2019 and was required to make 24 equal monthly payments of principal, plus accrued interest, from November 1, 2019 through October 1, 2021, when all unpaid principal and interest became due and payable
Term loan facility				$ 20,000
Loan and Security Agreement [Member] \| Silicon Valley Bank [Member] \| Convertible Preferred Stock [Member]
Debt Instrument [Line Items]
Debt instrument, number of equal monthly installments \| Installment				24
Loan and Security Agreement [Member] \| Silicon Valley Bank [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Interest bear rate				1.50%
2019 Convertible Notes [Member]
Debt Instrument [Line Items]
Premium paid for capped call transactions							$ 28,400
2020 Convertible Notes [Member]
Debt Instrument [Line Items]
Premium paid for capped call transactions							43,100
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]
Principal amount						$ 348,800	$ 348,800
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%
Debt interest expense						6,900	$ 10,800
Amortization of debt discounts						3,400	5,300
Accrued semi annual coupon payable						3,400	5,300
Amortization of debt issuance costs						100	200
Debt issuance costs gross						8,100	8,100
Long-term debt						$ 348,800	$ 348,800			$ 142,600
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 $39.46 per share of common stock).
Conversion ratio							0.0253405
Conversion price \| $ / shares						$ 39.46	$ 39.46
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, stated percentage		3.50%
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] \| 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
Unsecured Promissory Note [Member] \| Golda Darty Partners S A [Member]
Debt Instrument [Line Items]
Principal amount		7,000			$ 7,000
Debt instrument, due and payment description							The promissory note accrued interest at a rate per annum of 8.0%, and was due and payable quarterly in arrears on the 19th day of each April, July, October and January.
Maturity date					Oct. 19, 2022
Long-term debt					$ 7,000
Debt instrument per diem interest amount		100
Loss on extinguishment of debt					$ 300
Warrant to purchase common stock \| shares					93,764,000
Exercise price per share \| $ / shares					$ 5.484
Accrued interest rate					8.00%
Repayment of related party due amount including diem interest		$ 7,100
Fair value of warrant					$ 400

Leases - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jan. 01, 2019
Lessee Lease Description [Line Items]
Operating lease asset	$ 12,959		$ 12,959		$ 14,110
Operating lease liability	13,399		$ 13,399		$ 14,466
Operating lease description			The Company enters into lease agreements with terms generally ranging from 2-7 years. Some of the Company’s lease agreements include Company options to extend the lease on a month to month basis or for set periods for up to five years. Many leases also include options to terminate the leases within one year or per other contractual terms. Renewal and termination options were generally not included in the lease term for the Company’s existing operating leases.
Operating lease, existence of option to extend			true
Operating lease maximum term of options to terminate lease			1 year
Operating lease expense	$ 1,000	$ 500	$ 2,000	$ 900
Minimum [Member]
Lessee Lease Description [Line Items]
Operating lease, term of contract	2 years		2 years
Maximum [Member]
Lessee Lease Description [Line Items]
Operating lease, term of contract	7 years		7 years
Operating lease options to extend lease	5 years		5 years
ASU 2016-02 [Member]
Lessee Lease Description [Line Items]
Operating lease asset						$ 5,500
Operating lease liability						5,500
Additional operating lease asset						9,800
Additional operating lease liability						$ 9,800

Leases - Schedule of Additional Information Related to Operating Lease Assets and Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Leases [Abstract]
Operating Lease Assets	$ 12,959	$ 14,110
Operating Lease Liabilities	$ 13,399	$ 14,466
Weighted Average Remaining Term in years	4 years 6 months 25 days	5 years 3 days
Weighted Average discount rate used to measure outstanding lease liabilities	8.30%	8.19%

Leases - Supplemental Cash Flow Information Related to Operating Leases (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Leases [Abstract]
Operating cash flows for operating leases	$ 2,056	$ 713
Operating lease assets obtained in exchange for lease obligations	$ 334	$ 7,287

Leases - Maturities of Operating Lease Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Leases [Abstract]
2020	$ 1,872
2021	3,519
2022	3,283
2023	3,288
2024 and thereafter	4,107
Total future minimum lease payments less	16,069
Imputed interest	(2,670)
Operating Lease Liabilities	$ 13,399	$ 14,466

Marketable Securities - Schedule of Amortized Cost, Gross Unrealized Holding Losses and Fair Value of Available-for-Sale Debt Securities by Type of Security (Detail) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Available for sale securities:
Fair Value		$ 0
U.S. Government-Related Obligations [Member]
Available for sale securities:
Amortized Cost	$ 514,924,000
Gross Unrealized Holding Gains	555,000
Gross Unrealized Holding Losses	3,000
Fair Value	$ 515,476,000

Marketable Securities - Additional Information (Detail)	Dec. 31, 2019 USD ($)
Investments Debt And Equity Securities [Abstract]
Available-for-sale securities	$ 0

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
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ 258,997	$ 34,229	$ 224,755	$ 160,972
Net other comprehensive income (loss)	(681)	1,164	(1)	2
Ending balance	232,064	258,997	159,086	224,755
Unrealized Gains (Losses) from Marketable Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	1,394
Net other comprehensive income (loss)	(842)	1,394
Ending balance	552	1,394
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(384)	(154)	(121)	(123)
Net other comprehensive income (loss)	161	(230)	(1)	2
Ending balance	(223)	(384)	(122)	(121)
Total Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	1,010	(154)	(121)	(123)
Ending balance	$ 329	$ 1,010	$ (122)	$ (121)

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	Jun. 30, 2020	Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 314,268	$ 281,314
Total Financial Liabilities	378,732	149,496
Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	273,452	281,314
Bank Certificates of Deposit [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	40,816
Convertible Senior Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	378,732	149,496
Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	314,268	281,314
Level 1 [Member] \| Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	273,452	281,314
Level 1 [Member] \| Bank Certificates of Deposit [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	40,816
Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	378,732	149,496
Level 3 [Member] \| Convertible Senior Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	$ 378,732	$ 149,496

Fair Value Measurements - Additional Information (Detail) - Level 3 [Member] - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Percentage of cost of borrowing	15.08%
SFJ Agreement [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Percentage of cost of borrowing	8.00%
Convertible Senior Notes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Convertible notes	$ 378.7	$ 149.5
Convertible notes, interest rate	3.50%	3.50%

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	Jun. 30, 2020	Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 515,476
Total Financial Liabilities	220,475	$ 134,839
Marketable Securities [Member] \| US Government Agency [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	19,982
Marketable Securities [Member] \| US Government Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	495,494
Development Derivative Liability [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	220,475	134,839
Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	515,476
Level 1 [Member] \| Marketable Securities [Member] \| US Government Agency [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	19,982
Level 1 [Member] \| Marketable Securities [Member] \| US Government Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	495,494
Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	220,475	134,839
Level 3 [Member] \| Development Derivative Liability [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	$ 220,475	$ 134,839

Refundable Research and Development Credit and Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Expense Benefit Continuing Operations [Abstract]
Current income tax expense or benefits	$ 0	$ 0	$ 0	$ 0
Deferred income tax expense or benefits	$ 0	$ 0	$ 0	$ 0

Commitments and Contingencies - Additional Information (Detail) - 6 months ended Jun. 30, 2020 SFr in Thousands	USD ($) ft²	CHF (SFr)	CHF (SFr) ft²
Commitments And Contingencies [Line Items]
Base rent payable	$ 16,069,000
Estimated termination costs and other fees	1,800,000
Non-cancellable purchase commitments	$ 14,100,000
Minimum [Member]
Commitments And Contingencies [Line Items]
Operating lease, term of contract	2 years		2 years
Payment of royalty fees	3.00%	3.00%
Maximum [Member]
Commitments And Contingencies [Line Items]
Operating lease, term of contract	7 years		7 years
Future milestone payments	$ 15,000,000.0
Payment of royalty fees	6.00%	6.00%
Watertown, Massachusetts [Member]
Commitments And Contingencies [Line Items]
Operating lease, term of contract	85 months		85 months
Area of operating lease in Square feet/square meter \| ft²	9,704		9,704
Initial monthly lease payments per month	$ 60,000
Base rent payable	$ 5,400,000
Lease commencement date	Aug. 06, 2020	Aug. 06, 2020
Switzerland [Member]
Commitments And Contingencies [Line Items]
Operating lease, term of contract	60 months		60 months
Area of operating lease in Square feet/square meter \| ft²	938		938
Initial monthly lease payments per month \| SFr		SFr 38
Base rent payable \| SFr			SFr 2,300
Lease commencement date	Jul. 01, 2020	Jul. 01, 2020

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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	25,358	9,109	25,358	9,109
Convertible Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	13,177		13,177
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	11,832	9,095	11,832	9,095
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	349		349
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount		14		14

Related Party Transaction - Additional Information (Detail) - Revon [Member] - License Agreement and Services Agreement [Member] $ in Millions	May 01, 2018 USD ($)
Related Party Transaction [Line Items]
Annual license fee	$ 0.2
Related party transaction, initial term	2 years
Exclusive license option, thereafter	$ 0.4
Development service costs	$ 0.3