Apellis Pharmaceuticals (APLS) 10-Q 8 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 02, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
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		87,295,371
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

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 283,745	$ 565,779
Marketable securities	146,566	311,869
Accounts receivable	3,522
Inventory	1,677	0
Prepaid assets	17,374	11,400
Restricted cash	1,563	1,266
Other current assets	20,980	26,878
Total current assets	475,427	917,192
Non-current Assets:
Right-of-use assets	20,930	17,719
Property and equipment, net	6,509	6,803
Other assets	22,823	18,855
Total assets	525,689	960,569
Current liabilities:
Accounts payable	4,984	8,477
Accrued expenses	69,847	111,935
Current portion of development derivative liability	15,334	4,230
Current portion of right of use liabilities	4,072	3,685
Total current liabilities	94,237	128,327
Long-term liabilities:
Convertible senior notes	189,610	358,830
Development derivative liability	281,017	253,638
Operating lease liabilities	18,150	15,217
Total liabilities	583,014	756,012
Commitments and contingencies (Note 14)
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized, and zero shares issued and outstanding at September 30, 2021 and December 31, 2020	0	0
Common stock, $0.0001 par value; 200,000 shares authorized at September 30, 2021 and December 31, 2020; 87,219 shares issued and outstanding at September 30, 2021, and 76,130 shares issued and outstanding at December 31, 2020	9	8
Additional paid-in capital	1,453,431	1,131,013
Accumulated other comprehensive loss	(2,010)	(117)
Accumulated deficit	(1,508,755)	(926,347)
Total stockholders' equity	(57,325)	204,557
Total liabilities and stockholders' equity	$ 525,689	$ 960,569

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, issued	0	0
Preferred stock, outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, issued	87,219,000	76,130,000
Common stock, outstanding	87,219,000	76,130,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Income/(Loss) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue:
Revenue	$ 5,650	$ 646	$ 6,273	$ 646
Operating expenses:
Cost of sales	149		149
Research and development	87,733	93,207	267,688	249,584
Cost of research collaboration			50,000
General and administrative	45,763	36,991	135,309	94,909
Total operating expenses:	133,645	130,198	453,146	344,493
Net operating loss	(127,995)	(129,552)	(446,873)	(343,847)
Loss on conversion of debt	(61,102)		(100,589)
(Loss)/gain from remeasurement of development derivative liability	(4,219)	2,697	(42,483)	(62,939)
Interest income	144	670	381	3,970
Interest expense	(2,282)	(9,499)	(10,223)	(20,327)
Other (expense)/income, net	(117)	(16)	1,366	4
Net loss	(195,571)	(135,700)	(598,421)	(423,139)
Other comprehensive (loss)/gain:
Unrealized (loss)/gain on marketable securities	(25)	(430)	19	122
Foreign currency loss	(156)	(1,658)	(1,912)	(1,727)
Total other comprehensive loss	(181)	(2,088)	(1,893)	(1,605)
Comprehensive loss, net of tax	$ (195,752)	$ (137,788)	$ (600,314)	$ (424,744)
Net loss per common share, basic and diluted	$ (2.28)	$ (1.79)	$ (7.31)	$ (5.65)
Weighted-average number of common shares used in net loss per common share, basic and diluted	85,661	75,628	81,846	74,925
Product [Member]
Revenue:
Revenue	$ 5,314	$ 0	$ 5,937	$ 0
Licensing and other revenue [Member]
Revenue:
Revenue	$ 336	$ 646	$ 336	$ 646

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Changes in Stockholder's Equity (Unaudited) - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member]Cumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member]Cumulative Effect, Period of Adoption, Adjustment [Member]
Beginning balance at Dec. 31, 2019	$ 34,229		$ 6	$ 615,850		$ (154)	$ (581,473)
Beginning balance, Shares at Dec. 31, 2019			63,938
Issuance of common stock in follow-on offering, net of offering costs	381,458		$ 1	381,457
Issuance of common stock in follow-on offering, shares			10,925
Issuance of common stock upon exercise of stock options	1,674			1,674
Issuance of common stock upon exercise of stock options, shares			559
Share-based compensation expense	9,294			9,294
Unrealized gain (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	122
Net loss	(423,139)
Foreign currency gain (loss)	(1,727)
Ending balance at Sep. 30, 2020	105,840		$ 8	1,112,203		(1,759)	(1,004,612)
Ending balance, Shares at Sep. 30, 2020			75,694
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
Issuance of common stock to employee stock purchase plan	521			521
Issuance of common stock to employee stock purchase plan, shares			20
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)
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
Issuance of common stock upon exercise of stock options	1,127			1,127
Issuance of common stock upon exercise of stock options, shares			104
Share-based compensation expense	12,099			12,099
Unrealized gain (loss) on available-for-sale investments	(430)					(430)
Recognition of debt discount on convertible notes	(1,662)			(1,662)
Net loss	(135,700)						(135,700)
Foreign currency gain (loss)	(1,658)					(1,658)
Ending balance at Sep. 30, 2020	105,840		$ 8	1,112,203		(1,759)	(1,004,612)
Ending balance, Shares at Sep. 30, 2020			75,694
Beginning balance at Dec. 31, 2020	$ 204,557	$ (149,734)	$ 8	1,131,013	$ (165,747)	(117)	(926,347)	$ 16,013
Beginning balance, Shares at Dec. 31, 2020			76,130
Accounting Standards Update description	ASU 2020-06
Issuance of shares in exchange of Convertible Notes, including issuance costs	$ 162,258			162,258
Issuance of shares in exchange of Convertible Notes, including issuance costs. shares			3,976
Forfeiture of accrued interest in exchange of 2019 Convertible Notes	1,668			1,668
Issuance of common stock upon exercise of stock options	2,588			2,588
Issuance of common stock upon exercise of stock options, shares			285
Vesting of restricted stock units, net of shares withheld for taxes	(956)			(956)
Vesting of restricted stock units, net of shares withheld for taxes. shares			47
Share-based compensation expense	16,439			16,439
Unrealized gain (loss) on available-for-sale investments	79					79
Net loss	(183,659)						(183,659)
Foreign currency gain (loss)	(1,582)					(1,582)
Ending balance at Mar. 31, 2021	51,658		$ 8	1,147,263		(1,620)	(1,093,993)
Ending balance, Shares at Mar. 31, 2021			80,438
Beginning balance at Dec. 31, 2020	204,557	$ (149,734)	$ 8	1,131,013	$ (165,747)	(117)	(926,347)	$ 16,013
Beginning balance, Shares at Dec. 31, 2020			76,130
Unrealized gain (loss) on available-for-sale investments	19
Net loss	(598,421)
Foreign currency gain (loss)	(1,912)
Ending balance at Sep. 30, 2021	(57,325)		$ 9	1,453,431		(2,010)	(1,508,755)
Ending balance, Shares at Sep. 30, 2021			87,219
Beginning balance at Mar. 31, 2021	51,658		$ 8	1,147,263		(1,620)	(1,093,993)
Beginning balance, Shares at Mar. 31, 2021			80,438
Issuance of common stock upon exercise of stock options	7,062			7,062
Issuance of common stock upon exercise of stock options, shares			444
Vesting of restricted stock units, net of shares withheld for taxes	(233)			(233)
Vesting of restricted stock units, net of shares withheld for taxes. shares			11
Share-based compensation expense	17,722			17,722
Issuance of common stock to employee stock purchase plan	1,698			1,698
Issuance of common stock to employee stock purchase plan, shares			63
Unrealized gain (loss) on available-for-sale investments	(35)					(35)
Net loss	(219,191)						(219,191)
Foreign currency gain (loss)	(174)					(174)
Ending balance at Jun. 30, 2021	(141,493)		$ 8	1,173,512		(1,829)	(1,313,184)
Ending balance, Shares at Jun. 30, 2021			80,956
Issuance of shares in exchange of Convertible Notes, including issuance costs	258,105		$ 1	258,104
Issuance of shares in exchange of Convertible Notes, including issuance costs. shares			6,071
Forfeiture of accrued interest in exchange of 2019 Convertible Notes	2,503			2,503
Issuance of common stock upon exercise of stock options	2,480			2,480
Issuance of common stock upon exercise of stock options, shares			177
Vesting of restricted stock units, net of shares withheld for taxes	(362)			(362)
Vesting of restricted stock units, net of shares withheld for taxes. shares			15
Share-based compensation expense	17,194			17,194
Unrealized gain (loss) on available-for-sale investments	(25)					(25)
Net loss	(195,571)						(195,571)
Foreign currency gain (loss)	(156)					(156)
Ending balance at Sep. 30, 2021	$ (57,325)		$ 9	$ 1,453,431		$ (2,010)	$ (1,508,755)
Ending balance, Shares at Sep. 30, 2021			87,219

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating Activities
Net loss	$ (598,421)	$ (423,139)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	51,355	32,882
Loss on conversion of debt	100,589
Loss from remeasurement of development derivative liability	42,483	62,939
Forfeiture of accrued interest in exchange of convertible notes	4,171
Amortization of right-of-use assets	110	209
Depreciation expense	1,006	370
Amortization of discounts for convertible notes, net of financing costs	821	10,476
Changes in operating assets and liabilities:
Accounts receivable	(2,618)
Inventory	(1,677)
Prepaid assets	(5,862)	8,503
Other current assets	6,677	(627)
Other assets	(3,956)	(519)
Accounts payable	(3,213)	2,392
Accrued expenses	(42,092)	4,047
Net cash used in operating activities	(450,627)	(302,467)
Investing Activities
Purchase of property and equipment	(1,084)	(4,711)
Purchase of available-for-sale securities	(171,280)	(567,187)
Proceeds from maturity of available-for-sale securities	335,000	255,000
Net cash provided by (used in) investing activities	162,636	(316,898)
Financing Activities
Proceeds from issuance of common stock, net of issuance costs		381,423
Proceeds from / (payments for) development derivative liability	(4,000)	20,000
Payments for capped call transactions and associated costs		(43,112)
Proceeds from issuance of convertible notes, net of issuance costs		322,874
Proceeds from issuance of common stock under employee share purchase plan	1,698	521
Proceeds from exercise of stock options	12,131	4,155
Payments of employee tax withholding related to equity-based compensation	(1,551)
Net cash provided by financing activities	8,278	685,861
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(2,024)	(1,666)
Net increase in cash, cash equivalents and restricted cash	(281,737)	64,830
Cash, cash equivalents and restricted cash at beginning of period	567,045	351,985
Cash, cash equivalents and restricted cash at end of period	285,308	416,815
Reconciliation of cash, cash equivalents and restricted cash to the consolidated balance sheets:
Cash and cash equivalents	283,745	415,560
Restricted cash	1,563	1,255
Cash, cash equivalents and restricted cash at end of period	285,308	416,815
Supplemental Disclosure of Financing Activities
Cash paid for interest	10,265	$ 12,929
Convertible Notes exchanged for common stock	$ 327,276

Nature of Organization and Oper

Nature of Organization and Operations	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Organization and Operations	1. Nature of Organization and Operations Apellis Pharmaceuticals, Inc. (the “Company”) is a commercial-stage biopharmaceutical company focused on the discovery, development and commercialization 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 and commercializing 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, its ability to successfully commercialize its 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, the timing of the initiation of planned and future clinical trials, regulatory activities and commercialization of its products. Adoption of ASU 2020-06 Debt – Debt with Conversion and Other Options (Subtopic 470-20) Effective January 1, 2021, the Company early adopted ASU 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) Convertible Notes Exchange In In July 2021, the Company entered into separate, privately negotiated exchange agreements to modify the conversion terms with certain holders of the 2019 Convertible Notes and the 2020 Convertible Notes issued in May 2020 (the “2020 Convertible Notes”, and together with the 2019 Convertible Notes, the “Convertible Notes”). Under the terms of these exchange agreements, the holders exchanged approximately $201.1 million in aggregate principal amount of Convertible Notes held by them for an aggregate of 5,992,217 shares of common stock issued by the Company. The Company also has agreed to issue 78,419 shares for settlement of issuance costs paid to the Company’s advisor. The Company recognized a total loss on conversion of debt in the unaudited condensed consolidated statement of operations of $61.1 million for the three months ended September 2021. The Company recognized a total loss on the conversion of debt of $100.6 million in the unaudited condensed statement of operations for the nine months ended September 30, 2021. As of September 30, 2021, the Company held in treasury Convertible Notes in the principal amount of $ 327.2 million which notes have not been cancelled. See Note 7, Long Term Debt for additional information . Liquidity and Going Concern The accompanying unaudited condensed consolidated financial statements have been prepared on the basis of the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. As of November 8, 2021, the date of issuance of these unaudited condensed consolidated financial statements, the Company believes that its cash and cash equivalents and marketable securities of $430.3 The financial statements do not include any adjustments that might result from the outcome of this uncertainty. The Company has generated only limited revenues to date from product sales and has not achieved profitability. The Company’s plans to meet its short-term and longer-term operating cash flow requirements include: (1) obtaining additional debt or equity financing on terms that are favorable to the Company (2) achieving its projected revenues from sales of EMPAVELI, (3) entering into collaborative agreements with strategic partners to obtain funding, and (4) succeeding in its future operations. If the Company is not able to obtain the required funding for its operations, or to obtain funding on a timely basis on terms that are favorable to the Company, or to achieve its projected revenue, 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

Basis of Presentation	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	2. Basis of Presentation The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Apellis Australia Pty Ltd, Apellis Bermuda Limited, Apellis Germany GmbH, Apellis Ireland Ltd, Apellis Netherlands B.V., Apellis Switzerland GmbH, Apellis UK Limited, APL DEL Holdings LLC, APL Sales Corp I, LLC, APL PRG I, Corp., Apellis Cayman Holdings, Ltd., APL DEL Holdings II, LLC and Apellis MA Securities Corp. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”), for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP have been condensed or omitted and, accordingly, the consolidated balance sheet as of December 31, 2020 has been derived from audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair presentation of the Company’s financial information. The results of operations for the nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any other interim period or for any other future year. The accompanying unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2020 included in the Company’s Annual Report on Form 10-K filed with the SEC on February 25, 2021. Revenue Recognition The Company’s revenues consist of product sales of EMPAVELI and in past periods included revenues derived from its collaboration arrangement with Sobi. S ee Note 13, License and Collaboration Agreements, to our , for further discussion related to the Sobi Collaboration and License Agreement. The Company accounts for contracts with its customers in accordance with FASB ASC Topic 606, Revenue from Contracts with Customers, ( “ASC 606”). Pursuant to ASC 606, for arrangements or transactions between participants determined to be within the scope of the contracts with customers guidance, the Company performs the following five steps to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset. For performance obligations that are satisfied over time, the Company recognizes revenue using an input or output measure of progress that best depicts the satisfaction of the relevant performance obligation. Product Revenues For the three and nine-months ended September 30, 2021, the Company’s revenue from net product sales was generated in the United States following the FDA’s approval for marketing of EMPAVELI for the treatment of PNH in May 2021. The Company sells EMPAVELI principally through arrangements with specialty pharmacies (“SPs”) and specialty distributors (“SDs”), who are the Company’s customers. The customers subsequently resell the product to patients and health care providers. The Company applies the ASC 606 five step process discussed above to the contracts with SPs and SDs. The Company provides limited right of return to the customers in cases of shipment errors or expiring or defective products. Product revenues are recognized when the customers take control of the product, which typically occurs upon delivery to the customers. The Company recognizes revenue from product sales at the net sales price which includes estimates of variable consideration for which reserves are established and reflects each of these as a reduction to the revenue. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which the Company is entitled based on the terms of the contract. The amount of variable consideration that is included in the transaction price may be constrained. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from estimates, the Company may need to adjust its estimates, which would affect net revenue in the period of adjustment. The following are the Company’s significant categories of variable consideration: Distribution Fees : Distribution fees include distribution service fees paid to SPs and SDs based on a contractually fixed percentage of the wholesale acquisition cost (WAC), fees for data, and prompt payment discounts. The Company does not receive a distinct good or service in exchange for the payment. Distribution fees are recorded as an offset to revenue based on contractual terms at the time revenue from the sale is recognized. Chargebacks : Chargebacks are discounts and fees relate to contracts with various third-party payers including pharmacy benefit managers, private healthcare insurers and government healthcare programs that purchase from SDs at a discounted price. SDs charge back to the Company the difference between the price initially paid by SDs and the discounted price paid to SDs by these entities. The Company issues credit notes for the chargeback which are applied to future sales. Product Returns : Consistent with industry practice, the Company offers SPs and SDs limited product return rights for shipment errors or expiring or defective products; provided that the return is within a specified period around the product expiration date as set forth in the applicable individual distribution agreement. The Company does not allow product returns for product that has been dispensed to a patient. As the Company receives inventory reports from SPs and SDs and has visibility into the inventory distribution channel, it is able to make a reasonable estimate of future potential product returns based on this on-hand channel inventory data and sell-through data obtained from SPs and SDs. In arriving at its estimate for product returns, the Company also considers historical product returns (to the extent available), the underlying product demand, and industry data specific to the specialty pharmaceutical distribution industry. Licensing and Collaboration Revenue The Company analyzes license and collaboration arrangements pursuant to FASB ASC Topic 808, Collaborative Arrangement Guidance and Considerations, (“ASC 808”) to assess whether such arrangements, or transactions between arrangement participants, involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities or are more akin to a vendor-customer relationship. In making this evaluation, the Company considers whether the activities of the collaboration are considered to be distinct and deemed to be within the scope of the collaborative arrangement guidance or if they are more reflective of a vendor-customer relationship and, therefore, within the scope of ASC 606. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For elements of collaboration arrangements that are not accounted for pursuant to guidance in ASC 606, an appropriate recognition method is determined and applied consistently, generally by analogy to the revenue from contracts with customers guidance. Amounts related to transactions with a counterparty in a collaborative arrangement that is not a customer are presented as collaboration revenue and in a separate line item from revenue recognized from contracts with customers, if any, in the Company’s consolidated statements of operations. Pursuant to ASC 606, for arrangements or transactions between arrangement participants determined to be within the scope of the contracts with customers guidance, the Company performs the five step process discussed above to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations. The Company evaluates the performance obligations promised in the contract that are based on goods and services that will be transferred to the customer and determine whether those obligations are both (i) capable of being distinct and (ii) distinct in the context of the contract. Goods or services that meet these criteria are considered distinct performance obligations . Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset. For performance obligations that are satisfied over time, the Company recognizes revenue using an input or output measure of progress that best depicts the satisfaction of the relevant performance obligation. After contract inception, the transaction price is reassessed at every period end and updated for changes such as resolution of uncertain events. Any change in the overall transaction price is allocated to the performance obligations on the same methodology as at contract inception. See Note 13, License and Collaboration Agreements, for further discussion related to the Collaboration and License Agreement with Sobi Cost of Research Collaboration Arrangements The Company analyzes research collaboration arrangements pursuant to ASC 808 to assess whether such arrangements, or transactions between arrangement participants, involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. If e ach party is actively participating in this activity and exposed to significant risks and rewards related to the activity through each party’s costs will be accounted for under ASC 808 . Since ASC 808 does not provide recognition guidance, the Company refers to the guidance under FASB ASC 730, Research and Development, ( “ASC 730”) to arrangements involving payments by the Company . ASC 730 requires the Company to recognize research and developments costs as expense as incurred since there is no alternative use. The Company paid a $50.0 million up-front non-refundable payment to Beam Therapeutics, Inc. (“Beam”), in July 2021, which was recorded as a cost of research collaboration in research and development expenses during the nine months ended September 30, 2021. The Company did not record any cost of research collaboration in research and development expenses for the three months ended September 30, 2021. See Note 13 License and Collaboration Agreements for further discussion related to the Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk are primarily cash, cash equivalents, restricted cash, marketable securities and account receivables. The Company’s cash, cash equivalents, restricted cash and marketable securities are concentrated at financial institutions that management believes are creditworthy. Marketable securities consist of treasury notes and certificates of deposit. The Company's investment policy includes guidelines on the quality of the institutions and financial instruments and defines allowable investments that the Company believes minimizes the exposure to concentrations of credit risk. The Company has entered into distribution agreements with a limited number of SPs and SDs, and all of the Company’s product sales will be to these customers. For the quarter ended September 30, 2021, a small number of customers represented all of the Company’s product revenue and accounts receivable balance at September 30, 2021. The Company The Company does not currently have any of its own manufacturing facilities, and therefore it depends on an outsourced manufacturing strategy for the production of EMPAVELI for commercial use and for the production of its product candidates for clinical trials. The Company has contracts in place with one third-party manufacturer of commercial drug product and one third-party manufacturer of the drug substance that is approved for the production of EMPAVELI active pharmaceutical ingredient (API). Although there are potential sources of supply other than the Company’s existing suppliers, any new supplier would be required to qualify under applicable regulatory requirements. 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 7, Long-term Debt, Note 9, Marketable Securities, and Note 11, Fair Value Measurements, include cash and cash equivalents, accounts receivable, other receivables, accounts payable and accrued liabilities. Management believes that the carrying amounts of certain cash and cash equivalents, accounts receivable, other receivables, accounts payable and accrued expenses approximate the fair value due to the short-term nature of those instruments. Cash and Cash Equivalents Cash and cash equivalents are defined as cash in banks and investment instruments having maturities of three months or less from their acquisition date. The carrying amounts reported in the condensed consolidated balance sheets for certain cash and cash equivalents are valued at cost, which approximates their fair value. See Note 11, Fair Value Measurements, for additional information. Restricted Cash The Company is contingently liable under unused letters of credit with a bank, related to the Company’s customs import bond and facility lease agreements of $1.6 million and $1.3 million as of September 30, 2021 and December 31, 2020, respectively. The Company records as restricted cash the collateral used to secure these letters of credit. Accounts Receivable The Company’s accounts receivable primarily arise from product sales. They are generally stated at the invoiced amount and do not bear interest. The Company recognizes revenue from product sales at the net sales price which includes estimates of variable consideration for which reserves are established and reflects each of these as a reduction to the revenue. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which the Company is entitled based on the terms of the contract. The amount of variable consideration that is included in the transaction price may be constrained. The accounts receivable from product sales represents receivables due from the Company’s SPs or SDs. The Company has had no historical write-offs of its accounts receivable and its payment terms are generally 30-65 days. The Company monitors the financial performance and creditworthiness of its customers and provides reserves against trade receivables for expected credit losses that may result from a customer’s inability to pay. Amounts determined to be uncollectible are written-off against the established reserve. As of September 3 0 , 2021, the credit profiles for the Company’s customers were deemed to be in good standing and an allowance for credit losses was not considered necessary . Inventory Inventory is recorded at the lower of cost or net realizable value, with cost determined on a first-in, first-out basis. Inventory costs include third-party contract manufacturing, third-party packaging services, and freight. The Company primarily uses actual costs to determine the cost basis for its inventory. The Company periodically reviews its inventories to identify obsolete, slow moving, excess or otherwise unsaleable items. The determination of whether inventory costs will be realizable requires estimates by management. The Company does not have any obsolete inventory as of September 30, 2021. Prior to regulatory approval of its product candidates, the Company expenses costs associated with the manufacture of its product candidates to research and development expense unless the Company is reasonably certain such costs have future commercial use and net realizable value. When the Company believes regulatory approval and subsequent commercialization of our product candidates is probable, and the Company also expects future Prior to receiving FDA approval for EMPAVELI on May 14, 2021, the Company included in research and development expense the costs associated with the manufacture of EMPAVELI inventory to be sold upon commercialization. As a result, the manufacturing costs related to the EMPAVELI inventory build-up incurred before FDA approval were already expensed in a prior period and are therefore excluded from the cost of goods sold for the three and nine months ended September 30, 2021. Foreign Currency The financial position and results of operations of the Company's Australian, Irish and German subsidiaries are measured using the foreign subsidiary's local currency. Revenues and expenses of the subsidiaries have been translated into U.S. dollars at average exchange rates prevailing during the respective periods. Assets and liabilities have been translated at the rates of exchange on the balance sheet date. The resulting translation gain and loss adjustments are recorded directly as a separate component of stockholders’ equity .

Product Revenues, Accounts Rece

Product Revenues, Accounts Receivable, and Reserves for Product Sales	9 Months Ended
	Sep. 30, 2021
Product Revenues Accounts Receivable And Reserves For Product Sales [Abstract]
Product Revenues, Accounts Receivable, and Reserves for Product Sales	3. Product Revenues, Accounts Receivable, and Reserves for Product Sales The Company received FDA approval for the sale of EMPAVELI in the United States in May 2021. The Company’s product revenues, net of sales discounts and allowances and reserves, for the three and nine months ended September 30, 2021 consist of $5.3 million and $5.9 million, respectively, of sales of EMPAVELI to SPs and SDs. The Company did not have product revenue in 2020. The Company’s accounts receivable balance of $3.5 million as of September 30, 2021 consists of EMPAVELI product sales receivable, net of discounts and allowances. The Company does not have a reserve against its receivable balance. The Company’s product sales reserves totaling $0.3 million are included in accrued expenses on the Company’s unaudited consolidated balance sheet as of September 30, 2021. The Company did not have accounts receivable or product reserve balances as of December 31, 2020 .

Inventory

Inventory	9 Months Ended
	Sep. 30, 2021
Inventory Disclosure [Abstract]
Inventory	4. The Company’s inventory of EMPAVELI as of September 30, 2021 consisted of $1.4 million of semi-finished goods and $0.3 million of finished goods. The Company did not have inventory as of December 31, 2020.

Prepaid Assets and Accrued Expe

Prepaid Assets and Accrued Expenses	9 Months Ended
	Sep. 30, 2021
Prepaid Assets And Accrued Expenses [Abstract]
Prepaid Assets And Accrued Expenses	5. Prepaid Assets and Accrued Expenses Prepaid assets include $12.0 million and $8.0 million of prepaid research and development costs as of September 30, 2021 and December 31, 2020, respectively. Accrued expenses are as follows (in thousands): September 30, December 31, 2021 2020 Accrued research and development $ 28,670 $ 47,879 Accrued license fee — 25,050 Accrued payroll liabilities 27,124 22,896 Other 14,053 16,110 Total $ 69,847 $ 111,935

Development Derivative Liabilit

Development Derivative Liability	9 Months Ended
	Sep. 30, 2021
Research And Development [Abstract]
Development Derivative Liability	6. Development Derivative Liability On February 28, 2019, the Company entered into a development funding agreement, (the “SFJ Agreement”), with SFJ Pharmaceuticals Group (“SFJ”), under which SFJ agreed to provide funding to the Company to support the development of pegcetacoplan for the treatment of patients with paroxysmal nocturnal hemoglobinuria, (“PNH”). SFJ paid the Company $60.0 million following the signing of the agreement and agreed to pay the Company up to an additional $60.0 million in the aggregate in three equal installments upon the achievement of specified development milestones with respect to the Company’s Phase 3 program for systemic 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 systemic pegcetacoplan for the treatment of patients with PNH. As of September 30, 2021, the Company has received a total of $140.0 million from SFJ as the Company met milestones as identified in the agreement. The Company did not receive any funds under the SFJ agreement in 2021 or during the three months ended September 30, 2020. In the nine months ended September 30, 2020, the Company received $20.0 million, from SFJ. Under the SFJ Agreement following regulatory approval by the FDA for the use of systemic pegcetacoplan as a treatment for PNH the Company is obligated to pay SFJ an initial payment of $4.0 million and then an additional $226.0 million in the aggregate in six additional annual payments with the majority of the payments being made from the third anniversary to the sixth anniversary of regulatory approval. During the nine-months ended September 30, 2021, the Company paid $4.0 million to SFJ. Under the SFJ Agreement if regulatory approval is granted by the EMA for the use of systemic pegcetacoplan as a treatment for PNH, the Company will be obligated to pay SFJ an initial payment of up to $5.0 million and then up to an additional $226.0 million in the aggregate in six additional annual payments with the majority of the payments being made from the third anniversary to the sixth anniversary of regulatory approval. Additionally, the Company granted a security interest in all of its assets, excluding intellectual property and license agreements to which it is a party. In connection with the grant of the security interest, the Company agreed to certain affirmative and negative covenants, including restrictions on its ability to pay dividends, incur additional debt or enter into licensing transactions with respect to its intellectual property, other than specified types of licenses. The SFJ Agreement is presented as a derivative liability on the condensed consolidated balance sheet and is considered a level three derivative, and, as such, is recorded at fair value and remeasured each quarter. The change in fair value due to the remeasurement of the development derivative liability resulted in a $ 4.2 million loss and a $ million gain for the three months ended September 3 0 , 2021 and 2020 , respectively, recorded i n the unaudited condensed consolidated statement of operations . The change in fair value of the development derivative liability included in the unaudited condensed consolidated statement of operations for the nine months ended September 30, 2021 and 2020 resulted in a loss of $ 42.5 million and $ 62.9 million, respectively. The development derivative liability has a remeasured fair value of $ 296.3 million on the consolidated balance sheet at September 3 0 , 2021 . At September 3 0 , 2021, $ 15.3 million of the $ 296.3 million of the development derivative liability fair market value is included in current liabilities. The following table presents a rollforward of the development derivative liability (in thousands): For the Nine Months Ended September 30, 2021 2020 Balance at fair market value, January 1, $ 257,868 $ 134,839 Amounts received under the SFJ Agreement and SFJ Amendment — 20,000 Loss recorded in loss from remeasurement of development derivative liability 17,084 68,406 Balance at fair market value, March 31, 274,952 223,245 Amounts repaid under the SFJ Agreement and SFJ Amendment (4,000 ) — Loss/(gain) recorded in loss from remeasurement of development derivative liability 21,180 (2,770 ) Balance at fair market value, June 30, 292,132 220,475 Amounts received under the SFJ agreement and SFJ amendment — — Loss/(gain) recorded in loss from remeasurement of development derivative liability 4,219 (2,697 ) Balance at fair market value, September 30, $ 296,351 $ 217,778 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 EMA approval, (iii) SFJ’s cost of borrowing (8.0%), and (iv) the Company’s cost of borrowing (11.9%). SFJ’s implied cost of borrowing was 8.0% and the Company’s implied cost of borrowing was 11.9% 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

Long-term Debt	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Long-term Debt	7. Long-term Debt Convertible Senior Notes On September 16, 2019, the Company completed a private offering of the 2019 Convertible Notes with an aggregate principal amount of $220.0 million issued pursuant to an indenture (the “Indenture”) with U.S. Bank National Association, as trustee. The net proceeds from the sale of the 2019 Convertible Notes were approximately $212.9 million after deducting the initial purchasers’ discounts and commissions of $6.6 million and offering expenses of $0.5 million by the Company. The Company used $28.4 million of the net proceeds from the sale of the 2019 Convertible Notes to pay the cost of the capped call transactions in September 2019 described below. On May 12, The Convertible Notes are senior unsecured obligations of the Company and bear interest at a rate of 3.5% per year payable semiannually in arrears on March 15 and September 15 of each year, beginning on March 15, 2020. The Convertible Notes will mature on September 15, 2026, unless converted earlier, redeemed or repurchased in accordance with their terms. The Convertible Notes are convertible into shares of the Company’s common stock at an initial conversion rate of 25.3405 shares per $1,000 principal amount of Convertible Notes (equivalent to an initial conversion price of approximately $39.4625 per share of common stock). The conversion rate is subject to customary anti-dilution adjustments. In addition, following certain events that occur prior to the maturity date or if the Company deliver a notice of redemption, the Company will increase the conversion rate for a holder who elects to convert its Convertible Notes in connection with such corporate event or a notice of redemption, as the case may be, in certain circumstances as provided in the indenture. Prior to March 15, 2026, the Convertible Notes are convertible only under the following circumstances: • during any calendar quarter, if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; • during the five business day period after any five consecutive trading day period in which the trading price per $1,000 principal amount of the Convertible Notes for each such trading day was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such trading day; • if the Company calls any or all of the Convertible Notes for redemption, at any time prior to the close of business on the second scheduled trading day immediately preceding the redemption date; or • upon the occurrence of corporate events specified in the Indenture. On or after March 15, 2026 until the close of business on the second scheduled trading day immediately preceding the maturity date of the Convertible Notes, holders may convert the Convertible Notes at any time regardless of the foregoing circumstances. Upon conversion of the Convertible Notes, the Company will pay or deliver, as the case may be, cash, shares of the Company’s common stock or a combination of cash and shares of common stock, at the Company’s election. Prior to September 20, 2023, the Company may not redeem the Convertible Notes. The Company may redeem for cash all or a portion of the Convertible Notes, at its option, on or after September 20, 2023 if the last reported sale price of the Company’s common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive), including the trading day immediately preceding the date on which the Company provides a notice of redemption, during any 30 consecutive trading day period ending on, and including, the trading day immediately preceding the date on which the Company provides notice of redemption. The redemption price will be equal to 100% of the principal amount of the Convertible Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. If the Company undergoes a “fundamental change,” as defined in the Indenture, prior to maturity, subject to certain conditions, holders may require the Company to repurchase for cash all or any portion of their Convertible Notes at a fundamental change repurchase price equal to 100% of the principal amount of the notes to be repurchased, plus any accrued and unpaid interest to, but excluding, the fundamental change repurchase date. Prior to the adoption of ASU 2020-06 effective January 1, 2021, t he Company used an effective interest rate of 10.5% to determine the liability component of the 2019 and 2020 Convertible Notes. This resulted in the recognition of $145.1 million and $204.5 million as the liability component of the 2019 and 2020 Convertible Notes, respectively and the recognition of the residual amount of $74.9 million and $95.5 million as the debt discount with a corresponding increase to additional paid in capital for the equity component of the 2019 and 2020 Convertible Notes, respectively. The 2020 Convertible Notes aggregate debt issuance costs of $6.0 million were allocated to the liability and equity components in the amounts of $3.7 and $2.3 million, respectively. The 2019 Convertible Notes aggregate debt issuance costs of $7.1 million were allocated to the liability and equity components in the amounts of $4.7 million and $2.4 million, respectively. Effective January 1, 2021, the Company adopted ASU 2020-06 using the modified retrospective method. Upon adoption, the Company increased net debt and reduced net equity by $149.7 million. The $149.7 million consisted of several items. The first item is the reclassification from equity to debt of the residual amounts originally identified as the equity components of the 2019 and 2020 Convertible Notes of $74.9 million and $95.5 million, respectively. The equity component reclassification was offset by the adjustment to retained earnings for the reversal of previous non-cash interest expense recorded for the amortization of the equity components of $17.1 million. The second item is the reclassification from equity to debt of the debt issuance costs originally allocated to equity for the 2019 and 2020 Convertible Notes of $ million and $ million, respectively . The debt issuance costs reclass ification was offset by the a djustment to retained earnings for previous amortization of the debt issuance costs recorded of $ million. In January 2021 and in July 2021, the Company entered into separate, privately negotiated exchange agreements to modify the conversion terms with certain holders of its 2019 Convertible Notes. Under the terms of these exchange agreements, in January 2021 and July 2021, the holders exchanged approximately $126.1 million of 2019 Convertible Notes and $201.1 million of Convertible Notes, respectively, in aggregate principal amount held by them for an aggregate of 3,906,869 shares and 5,992,217 shares, respectively, of common stock issued by the Company. In accordance with ASC topic 470-20, “ Debt For the January 2021 transaction, the Company reduced net debt outstanding and increased net equity on the consolidated balance sheet by $122.8 million, consisting of the par value of the 2019 Convertible Notes exchanged of $126.1 million less the $3.3 million of remaining debt issuance costs associated with the exchanged notes. The Company also increased shares outstanding by 3,906,869 shares consisting of 3,196,172 shares issued at the initial conversion rate in the Indenture of 25.3405 plus an additional 710,697 shares. Additionally, the Company issued 69,491 shares as settlement of debt issuance costs paid to the Company’s advisor in connection with the conversion transaction. The Company recorded a loss on conversion of debt of $39.5 million comprised of $36.4 million related to the value of the shares issued in excess of the original conversion terms at the fair market value and $3.1 million for the value of the 69,491 shares issued in payment of issuance costs. Upon exchange of the 2019 Convertible Notes, the holders forfeited accrued interest through the date of the exchange of $1.7 million, which the Company charged to interest expense and to equity. For the July 2021 transaction, the Company reduced net debt outstanding and increased net equity on the consolidated balance sheet by $197.0 million, consisting of the par value of the 2019 and 2020 Convertible Notes exchanged of $201.1 million less the $4.1 million of remaining debt issuance costs associated with the exchanged notes. The Company also increased shares outstanding by 5,992,217 shares consisting of 5,097,166 shares issued at the initial conversion rate in the Indenture of 25.3405 plus an additional 895,051 shares. Additionally, the Company issued 78,419 shares as settlement of debt issuance costs paid to the Company’s advisor in connection with the conversion transaction. For the three months ended September 30, 2021, the Company recorded a loss on conversion of debt of $61.1 million comprised of $55.9 million related to the value of the shares issued in excess of the original conversion terms at the fair market value and $5.2 million for the value of the 78,419 shares issued in payment of issuance costs. Upon exchange of the 2019 and 2020 Convertible Notes, the holders forfeited accrued interest through the date of the exchange of $2.5 million, which the Company charged to interest expense and to equity. During the quarter ended September 30, 2021, the Convertible Notes were convertible at the option of the holders, and certain holders of the Convertible Notes converted approximately $0.7 million of aggregate principal amount of Convertible Notes into an aggregate of 18,775 shares. The shares were issued in October 2021. The Company recognized a total loss on the conversion of debt of $100.6 million of loss on conversion of debt in the unaudited condensed statement of operations for the nine months ended September 30, 2021. As of September 30, 2021, the Company held in treasury Convertible Notes in principal amount of $327.2 million which notes had not been cancelled. Interest expense for the Convertible Notes was $2.3 million and $10.2 million for the three and nine months ended September 30, 2021, respectively. For the three months ended September 30, 2021, interest expense included accrued semi-annual coupon payable of $2.1 million and amortization of debt issuance costs of $0.2 million. For the nine months ended September 30, 2021, interest expense included accrued semi-annual coupon payable of $9.4 million and amortization of debt issuance costs of $0.8 million . The aggregate principal balance of the Convertible Notes, net of unamortized debt issuance costs, as of September 30, 2021 and December 31, 2020 was $189.6 million and $358.8 million respectively. Capped Call Transactions On September 11, 2019, and May 6, 2020 concurrently with the pricing of the 2019 Convertible Notes and the 2020 Convertible Notes, respectively, the Company entered into capped call transactions with two counterparties. The capped call transactions are expected generally to reduce the potential dilution to the Company’s common stock upon any conversion of Convertible Notes and/or offset any cash payments the Company is required to make in excess of the principal amount of converted Convertible Notes, as the case may be, in the event that the market price per share of the Company’s common stock, as measured under the terms of the capped call transactions, is greater than the strike price of the capped call transactions, which is initially $ 39.4625 (the conversion price of the Convertible N otes) and is subject to anti-dilution adjustments substantially similar to those applicable to the conversion rate of such Convertible N otes. 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

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	8. Leases On January 1, 2019, the Company adopted ASU 2016-02 Leases (Topic 842) 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. options to terminate the leases within one year or per other contractual terms. As of September 30, 2021 and December 31, 2020, all leases were classified as operating lease assets and liabilities. Additional information related to the operating lease assets and liabilities is as follows (in thousands): September 30, December 31, 2021 2020 Operating Lease Assets $ 20,930 $ 17,719 Operating Lease Liabilities $ 22,222 $ 18,902 Weighted Average Remaining Term in years 4.87 4.66 Weighted Average discount rate used to measure outstanding lease liabilities 7.71 % 7.74 % For the three months ended September 30, 2021 and 2020, the total lease cost for operating lease expense was $1.4 million and $1.1 million, respectively. For the nine months ended September 30, 2021 and 2020, the total lease cost for operating lease expense was $4.2 million and $3.1 million, respectively. Supplemental cash flow information related to operating leases for the nine months ended September 30 is as follows (in thousands): 2021 2020 Operating cash flows for operating leases $ 4,476 $ 3,322 Operating lease assets obtained in exchange for lease obligations $ 5,675 $ 6,664 The maturities of the Company’s operating lease liabilities as of September 30, 2021 are as follows (in thousands): 2021 $ 1,436 2022 5,561 2023 5,625 2024 4,862 2025 and thereafter 9,261 Total future minimum lease payments less 26,745 Imputed interest (4,523 ) Total operating lease liabilities $ 22,222

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2021
Investments Debt And Equity Securities [Abstract]
Marketable Securities	9. Marketable Securities The amortized cost, gross unrealized holding losses and fair value of available-for-sale debt securities by type of security as of September 30, 2021 and December 31, 2020 were as follows (in thousands): As of September 30, 2021 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Fair Value U.S. Government-related obligations $ 146,555 $ 11 $ — $ 146,566 As of December 31, 2020 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Fair Value U.S. Government-related obligations $ 311,877 $ 11 $ (19 ) $ 311,869 All available-for-sale securities mature in one year or less.

Other Comprehensive Income and

Other Comprehensive Income and Accumulated Other Comprehensive Income	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Other Comprehensive Income and Accumulated Other Comprehensive Income	10. Other Comprehensive Income and Accumulated Other Comprehensive Income The following tables summarize the changes in accumulated other comprehensive income/(loss), by component for the nine months ended September 30, 2021 and 2020 (in thousands): Unrealized Gains (Losses) from Marketable Securities Foreign Currency Translation Adjustment Total Accumulated Other Comprehensive Income (Loss) Balances, December 31, 2020 $ (8 ) $ (109 ) $ (117 ) Net other comprehensive income (loss) 79 (1,582 ) (1,503 ) Balances, March 31, 2021 71 (1,691 ) (1,620 ) Net other comprehensive income (loss) (35 ) (174 ) (209 ) Balances, June 30, 2021 36 (1,865 ) (1,829 ) Net other comprehensive income (loss) (25 ) (156 ) (181 ) Balances, September 30, 2021 $ 11 $ (2,021 ) $ (2,010 ) 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 Net other comprehensive income (loss) (430 ) (1,658 ) (2,088 ) Balances, September 30, 2020 $ 122 $ (1,881 ) $ (1,759 )

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	11 . Fair Value Measurements 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 following table presents the fair value of financial instruments recorded originally at amortized cost or fair value and not remeasured on a recurring basis (in thousands): September 30, 2021 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Cash and cash equivalents: Money market funds $ 254,088 $ — $ — $ 254,088 Total Financial Assets $ 254,088 $ — $ — $ 254,088 December 31, 2020 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Cash and cash equivalents Money market funds $ 427,515 $ — $ — $ 427,515 Bank certificates of deposit 43,577 — — 43,577 Total Financial Assets $ 471,092 $ — $ — $ 471,092 * The convertible notes were measured and recognized at fair value on the consolidated balance sheet at inception. The Company’s Convertible Notes are Level 1 category within the fair value level hierarchy at September 30, 2021 due to the adoption of ASU 2020-06. The fair value of the Convertible Notes was $241.2 million at September 30, 2021. At December 31, 2020, the Company’s Convertible Notes were Level 2 category within the fair value level hierarchy. At December 31, 2020, the fair value of debt was determined using broker quotes in a non-active market for valuation. As of December 31, 2020, the fair value of the debt component of the Company's Convertible Notes was $676.2 million. The Convertible Notes accrue a semi-annual coupon at an annual rate of 3.5%, which was included in accrued expenses in the consolidated balance sheets at September 30, 2021 and December 31, 2020. The following table presents the fair value of financial instruments recorded at fair value at inception and remeasured on a recurring basis (in thousands): September 30, 2021 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Marketable securities: US government obligations $ 146,566 — — $ 146,566 Total Financial Assets $ 146,566 $ — $ — $ 146,566 Financial Liabilities: Development derivative liability Development derivative liability $ — $ — $ 296,351 $ 296,351 Total Financial Liabilities $ — $ — $ 296,351 $ 296,351 December 31, 2020 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Cash and cash equivalents US government obligations $ 89,990 $ — $ — $ 89,990 Marketable securities: US government obligations 311,869 — — 311,869 Total Financial Assets $ 401,859 $ — $ — $ 401,859 Financial Liabilities: Development derivative liability Development derivative liability $ — $ — $ 257,868 $ 257,868 Total Financial Liabilities $ — $ — $ 257,868 $ 257,868 The fair value of the obligations under the SFJ Agreement is presented as a development derivative liability based on level 3 inputs. The derivative is valued using a scenario-based discounted cash flow method, whereby each scenario makes assumptions about the probability and timing of cash flows, and such cash flows are present valued using a risk-adjusted discount rate. The analysis is calibrated such that the value of the derivative as of the date of the SFJ Agreement was consistent with an arm’s-length transaction. Key inputs to the level 3 fair value model include (i) the probability and timing of achieving stated development milestones to receive the next tranches of funding, (ii) the probability and timing of achieving EMA approval, (iii) SFJ’s cost of borrowing (8.0%), and (iv) the Company’s cost of borrowing (11.9%). SFJ’s implied cost of borrowing was 8.0% and the Company’s implied cost of borrowing was 11.9% as of the reporting date. These implied costs of borrowing were determined assuming the SFJ Agreement was initially executed with arm’s-length terms.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes Deferred tax assets and deferred tax liabilities are determined based on temporary differences between the financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Company has recorded a full valuation allowance against its deferred tax assets for the period ended on September 30, 2021. The Company does not recognize a tax benefit for uncertain tax positions unless it is more likely than not that the position will be sustained upon examination by tax authorities, including resolution of any related appeals or litigation processes, based on the technical merits of the position. The tax benefit that is recorded for these positions is measured at the largest amount of cumulative benefit that has greater than a 50 percent likelihood of being realized upon ultimate settlement. Deferred tax assets that do not meet these recognition criteria are not recorded and the Company recognizes a liability for uncertain tax positions that may result in tax payments. If such unrecognized tax benefits were realized and not subject to valuation allowances, the entire amount would impact the tax provision. The Company has not recorded any amounts for unrecognized tax positions for the period ended on September 30, 2021. For the three and nine months ended September 30, 2021 and 2020, the Company did not record any current or deferred income tax expense or benefit.

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
License and Collaboration Agreements	13. License and Collaboration Agreements Sobi License and Collaboration Agreement On October 27, 2020, the Company and its subsidiaries Apellis Switzerland GmbH and APL DEL Holdings, LLC entered into a Collaboration and License Agreement with Sobi, concerning the development and commercialization of pegcetacoplan and specified other structurally and functionally similar compstatin analogues or derivatives for use systemically or for local non-ophthalmological administration (collectively referred to as the “Licensed Products”). Under the collaboration agreement, the Company granted Sobi an exclusive (subject to certain retained rights of the Company), sublicensable license of certain patent rights and know-how to develop and commercialize Licensed Products in all countries outside of the United States. The Company retains the right to commercialize Licensed Products in the United States, and, subject to specified limitations, to develop Licensed Products worldwide for commercialization in the United States. Under the collaboration agreement, the Company and Sobi have agreed to collaborate to develop Licensed Products for the treatment of PNH, cold agglutinin disease, hematopoietic stem cell transplantation-associated thrombotic microangiopathy, C3 glomerulopathy and immune complex membranoproliferative glomerulonephritis, and amyotrophic lateral sclerosis, and any other indications subsequently agreed upon by the parties, for commercialization by or on behalf of the Company in the United States and by or on behalf of Sobi outside of the United States. If the parties do not agree to jointly pursue any development activities for the Licensed Products (whether for an Initial Indication or otherwise), the party proposing to pursue such activities may conduct such activities at its sole expense (with the non-proposing party having the right to obtain rights to the data generated by such development activities by paying a specified percentage of that expense), subject to agreed-upon exceptions that limit each party’s unilateral development rights. The initial development plan sets forth the initial development activities to be conducted by each of the Company and Sobi, with the Company bearing all costs incurred in conducting the activities set forth in such initial development plan, as well as certain specified additional costs that are not included in the initial development plan that may be incurred by the parties in developing Licensed Products for PNH in the European Union and the United Kingdom. The Company and Sobi have formed several governance committees to oversee the development and manufacture, and to review and discuss the commercialization, of Licensed Products. The Company shall supply Licensed Products to Sobi for development and for commercialization outside of the United States in accordance with a supply agreement to be negotiated by the parties. The collaboration agreement grants Sobi the right to perform or have performed drug product manufacturing of Licensed Products for development and for commercialization outside the United States and to manufacture or have manufactured drug substance under certain circumstances. Sobi paid the Company an up-front payment of $250.0 million in November 2020 and has agreed to pay up to an aggregate of $915.0 million upon the achievement of specified one-time regulatory and commercial milestone events, including a $50.0 million milestone payment which would be payable upon the first regulatory and reimbursement approval for systemic pegcetacoplan in any major European country, and to reimburse the Company for up to $80.0 million in development costs. The Company will also be entitled to receive tiered, double-digit royalties (ranging from high teens to high twenties) on sales of Licensed Products outside of the United States, subject to customary deductions and third-party payment obligations, until the latest to occur of: (i) expiration of the last-to-expire of specified licensed patent rights; (ii) expiration of regulatory exclusivity; and (iii) ten (10) years after the first commercial sale of the applicable Licensed Product, in each case on a Licensed Product-by-Licensed Product and country-by-country basis. Under the collaboration agreement, the Company remains responsible for its license fee obligations (including royalty obligations) to the University of Pennsylvania as a licensor of the Company and for its payment obligations to SFJ. Sobi Accounting Analysis The Company has determined that the agreement is within the scope of ASC 808 as a contractual arrangement that involves a joint operating activity whereby both parties are (i) active participants in the activity and (ii) exposed to certain significant risks and rewards dependent on the commercial success of the activity. ASC Topic 808 does not address measurement or recognition matters but allows for analogizing to ASC 606. Pursuant to ASC 606, The Company identified the following material distinct promises under the Sobi Agreement: (1) licenses to develop and commercialize pegcetacoplan or, Licenses to IP, and (2) performance of research and development services. The Company determined the promises to be distinct because Sobi can benefit from each of the license and the development services on their own or with readily available services. The Company could have provided the license without any development services and Sobi would have been able to benefit from it by obtaining development services from another provider as the Licensed Products are at a more mature stage in their life cycle. Under the agreement, Sobi agreed to pay the Company i) a fixed amount of $250.0 million in an up-front payment ii) a fixed amount of an additional $80.0 million in development reimbursement payments, payable yearly in four tranches in amounts determined based upon actual expenses incurred by the Company; iii) up to an aggregate of $915.0 million upon the achievement of specified one-time regulatory and commercial milestone events; and iv) tiered, double-digit royalties, ranging from high teens to high twenties, on sales of Licensed Products outside of the United States, subject to customary deductions and third-party payment obligations. At contract inception, the $250.0 million non-refundable payment and the $80.0 million reimbursements were fixed proceeds. The Company evaluated whether Sobi is a customer for either of the distinct promises in the agreement. Under the Licenses to IP, the Company determined that Sobi is a customer as the know-how provided and the right granted by the Company to Sobi are outputs of the Company’s business activities for which the Company will receive consideration. With respect to research and development activity, management determined that there is no vendor relationship as performing research and development activities for others is not a part of the Company’s ongoing central operations. The milestone and royalty payments are subject to activities outside the control of the Company. Per ASC 606, the Company considers this to be a customer/ vendor relationship, therefore, the Company will include the regulatory milestone payments in the total transaction price when it is probable that a significant reversal of revenue would not occur in a future period. The Company will recognize commercial milestone and royalty revenue at the later of (i) when the related sales occur or (ii) when the performance obligation to which the commercial milestone or royalty has been allocated has been satisfied. In case of commercial milestone or royalty payments, the Company will recognize revenue in the same period that the sales are completed for which the Company is contractually entitled to the milestone or percentage-based royalty payment. To date, the Company has not recognized any commercial milestone or royalty revenue resulting from any of its licensing arrangements. Pursuant to ASC 606, for the year ended December 31, 2020 the Company recognized the $250.0 million in revenue as this is the amount allocated to the license. The $80.0 million reimbursement commitment for research and development activities does not constitute a customer/vendor relationship and thus is not in the scope of ASC 606. As ASC 808 does not include recognition guidance, the Company has established an accounting policy to recognize the payments under the reimbursement as a receivable on the balance sheet in an amount that is to be reimbursed based upon expense incurred by the Company, with a contra- research and development expense recognized in the statement of operations, over time as the expenses are incurred. Under the Sobi collaboration agreement, for the three and nine months ended September 30, 2021, the Company did not recognize licensing revenue. For the three and nine months ended September 30, 2021, the Company recognized $6.4 million and $23.6 million, respectively for contra-research and development expense in the unaudited condensed consolidated statement of operations related to the $80.0 million reimbursement commitment from Sobi. As of December 31, 2020, the Company had recorded a $43.0 million receivable for contra-research and development reimbursement in the unaudited condensed consolidated balance sheet, with $25.0 million and $18.0 million in current and long-term assets, respectively. The Company received a $25.0 million payment from Sobi in January 2021. As of September 30, 2021, the Company has recorded a receivable of $41.6 million for contra-research and development reimbursement from Sobi in the unaudited condensed consolidated balance sheet with $20.0 million and $21.6 million recognized in current assets and long term assets, respectively. University of Pennsylvania License Agreement The Company is a party to a license agreement with the Trustees of the University of Pennsylvania (“Penn”) for an exclusive, worldwide license to specified patent rights. The Company is required to pay annual maintenance fees of $0.1 million until the first sale of a licensed product. The Company is also required to make milestone payments aggregating up to $3.2 million based upon the achievement of specified development and regulatory milestones and up to $5.0 million based upon the achievement of specified annual sales milestones with respect to each licensed product, and to pay low single-digit royalties based on net sales of each licensed product and with minimum quarterly royalty thresholds. In addition, the Company is obligated to pay a specified portion of income it receives from sublicensees. In addition, the Company is also party to a license agreement with Penn for an exclusive, worldwide license to specified patent rights for the development and commercialization of products in fields of use, as defined therein. The Company is required to pay annual maintenance fees of $0.1 million until the first sale of a licensed product. The Company is required to make milestone payments aggregating up to $1.7 million, based upon the achievement of development and regulatory approval milestones, and up to $2.5 million, based upon the achievement of annual sales milestones with respect to each of the first two licensed products. The license agreement also requires the Company to pay low single digit royalties based on net sales of each licensed product, subject to minimum quarterly royalty thresholds. In addition, the Company is obligated to pay a specified portion of income it receives from sublicensees. In January 2021, the Company paid $25.0 million for sublicense fee owed to Penn related to the Sobi Agreement and another licensing transaction. As of December 31, 2020 the $25.0 million was recognized in accrued expenses on the consolidated balance sheet and recognized in license fees on the consolidated income statement. In August 2021 the Company paid $1.0 million to Penn upon the achievement of a development milestone. Beam Research Collaboration In June 2021, the Company entered into an exclusive five-year . T As part of the collaboration, the Company agreed to pay a $50.0 million up-front, non-refundable payment to Beam, which the Company paid in July 2021, and the Company is to pay an additional $25.0 million payment on the first anniversary of the agreement on June 30, 2022. The Company has not recognized the $25.0 million payment in the unaudited condensed financial statements as of September 30, 2021, as the payment is not yet probable. The Company and Beam will each be responsible for their own costs during the research collaboration. If and after the opt-in license rights are exercised for each of the up to six programs, Beam will be eligible to receive development, regulatory and sales milestones from the Company, as well as royalty payments on sales. The collaboration has an initial term of five years and may be extended up to two years on a per year program-by-program basis. The Company analyzed the research collaboration agreement pursuant to ASC 808 to assess whether the agreement involved joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. Since each party is actively participating in this activity and exposed to significant risks and rewards related to the activity through each party’s costs will be accounted for under ASC 808. Since ASC 808 does not provide recognition guidance, the Company referred to the guidance under ASC 730 to arrangements involving payments by the Company . ASC 730 requires the Company to recognize research and developments costs as expense as incurred since the payment was made for the use of Beam’s intellectual property and research and development services and there is no alternative use. The Company recorded the $50.0 million up-front, non-refundable payment to Beam, recorded as a cost of research collaboration in research and development expenses for the nine months ended September 30, 2021. The Company did not incur cost of research collaboration expense in research and development expenses for the three months ended September 30, 2021. Other Agreements In addition to the license agreements with Penn, and Beam, the Company contracts to conduct research and development activities with third parties. Certain of these contracts commit the Company to pay future milestone payments up to $15.0 million or to pay royalty fees ranging from 3-6% if any of the research results in regulatory approval or commercial revenue for a product.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	14. Commitments and Contingencies The Company contracts to conduct research and development activities with third parties. The scope of the services under the research and development contracts can be modified and the contracts cancelled by the Company upon written notice. In some instances, the contracts may be cancelled by the third party upon written notice. If the Company were to cancel these contracts as of September 30, 2021, the Company would be required to pay certain termination costs and other fees of approximately $2.4 million that would be incurred in future periods. The Company has certain non-cancellable purchase obligations related to the manufacturing of drug substance and drug product, primarily with Bachem Americas, Inc., and Bachem AG, collectively (“Bachem”) for the drug substance for the finished dosage form of pegcetacoplan and with NOF Corporation and NOF America Corporation, collectively, (“NOF”) for a component of pegcetacoplan. As of November 8, 2021, the date of this Quarterly Report on Form 10-Q , the Company has remaining non-cancellable purchase commitments through September 2022 in the amount of approximately $65.2 million. The Company has additional purchase commitments of approximately $37.0 million through December of 2023. Through September 2023, the Company has the option to terminate the $37.0 million minimum commitments at a cost of approximately $12.8 million. To the extent the minimum purchase commitments of $37.0 million are not met by December 31, 2023, the Company will incur costs of up to $19.7 million. Following regulatory approval of EMPAVELI by the FDA in May 2021 and any potential future approval by the EMA of systemic pegcetacoplan for the treatment of PNH, the Company has or will have certain payment and other obligations under the SFJ Agreement, which are discussed above in Note 6. The Company is a party to a master lease agreement under which the Company leases vehicles with initial terms of 36 months from the date of delivery. If the Company were unable to take delivery of a previously ordered vehicle, the Company may incur nominal fees. Indemnifications —In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend indemnified parties for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third-party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has not incurred any cost to defend lawsuits or settle claims related to these indemnification provisions. Legal —During the normal course of business, the Company may be a party to legal claims that may not be covered by insurance. Management does not believe that any such claims would have a material impact on the Company’s consolidated financial statements.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss per Share	15. Net Loss per Share Since the Company was in a loss position for all periods presented, basic net loss per common share is the same as diluted net loss per common share for all periods presented as the inclusion of all potential common shares outstanding would have been anti-dilutive. Convertible notes and shares outstanding presented below were excluded from the calculation of diluted net loss per share, prior to the use of the treasury stock method, as their effect is anti-dilutive (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2021 2020 2021 2020 Convertible notes 4,884 13,177 4,884 13,177 Common stock options 12,954 12,174 12,954 12,174 Restricted stock units 1,071 433 1,071 433 Total 18,909 25,784 18,909 25,784

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Apellis Australia Pty Ltd, Apellis Bermuda Limited, Apellis Germany GmbH, Apellis Ireland Ltd, Apellis Netherlands B.V., Apellis Switzerland GmbH, Apellis UK Limited, APL DEL Holdings LLC, APL Sales Corp I, LLC, APL PRG I, Corp., Apellis Cayman Holdings, Ltd., APL DEL Holdings II, LLC and Apellis MA Securities Corp. All intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”), for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP have been condensed or omitted and, accordingly, the consolidated balance sheet as of December 31, 2020 has been derived from audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair presentation of the Company’s financial information. The results of operations for the nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any other interim period or for any other future year. The accompanying unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2020 included in the Company’s Annual Report on Form 10-K filed with the SEC on February 25, 2021.
Revenue Recognition	Revenue Recognition The Company’s revenues consist of product sales of EMPAVELI and in past periods included revenues derived from its collaboration arrangement with Sobi. S ee Note 13, License and Collaboration Agreements, to our , for further discussion related to the Sobi Collaboration and License Agreement. The Company accounts for contracts with its customers in accordance with FASB ASC Topic 606, Revenue from Contracts with Customers, ( “ASC 606”). Pursuant to ASC 606, for arrangements or transactions between participants determined to be within the scope of the contracts with customers guidance, the Company performs the following five steps to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset. For performance obligations that are satisfied over time, the Company recognizes revenue using an input or output measure of progress that best depicts the satisfaction of the relevant performance obligation.
Product Revenues	Product Revenues For the three and nine-months ended September 30, 2021, the Company’s revenue from net product sales was generated in the United States following the FDA’s approval for marketing of EMPAVELI for the treatment of PNH in May 2021. The Company sells EMPAVELI principally through arrangements with specialty pharmacies (“SPs”) and specialty distributors (“SDs”), who are the Company’s customers. The customers subsequently resell the product to patients and health care providers. The Company applies the ASC 606 five step process discussed above to the contracts with SPs and SDs. The Company provides limited right of return to the customers in cases of shipment errors or expiring or defective products. Product revenues are recognized when the customers take control of the product, which typically occurs upon delivery to the customers. The Company recognizes revenue from product sales at the net sales price which includes estimates of variable consideration for which reserves are established and reflects each of these as a reduction to the revenue. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which the Company is entitled based on the terms of the contract. The amount of variable consideration that is included in the transaction price may be constrained. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from estimates, the Company may need to adjust its estimates, which would affect net revenue in the period of adjustment. The following are the Company’s significant categories of variable consideration: Distribution Fees : Distribution fees include distribution service fees paid to SPs and SDs based on a contractually fixed percentage of the wholesale acquisition cost (WAC), fees for data, and prompt payment discounts. The Company does not receive a distinct good or service in exchange for the payment. Distribution fees are recorded as an offset to revenue based on contractual terms at the time revenue from the sale is recognized. Chargebacks : Chargebacks are discounts and fees relate to contracts with various third-party payers including pharmacy benefit managers, private healthcare insurers and government healthcare programs that purchase from SDs at a discounted price. SDs charge back to the Company the difference between the price initially paid by SDs and the discounted price paid to SDs by these entities. The Company issues credit notes for the chargeback which are applied to future sales. Product Returns : Consistent with industry practice, the Company offers SPs and SDs limited product return rights for shipment errors or expiring or defective products; provided that the return is within a specified period around the product expiration date as set forth in the applicable individual distribution agreement. The Company does not allow product returns for product that has been dispensed to a patient. As the Company receives inventory reports from SPs and SDs and has visibility into the inventory distribution channel, it is able to make a reasonable estimate of future potential product returns based on this on-hand channel inventory data and sell-through data obtained from SPs and SDs. In arriving at its estimate for product returns, the Company also considers historical product returns (to the extent available), the underlying product demand, and industry data specific to the specialty pharmaceutical distribution industry.
Licensing and Collaboration Revenue	Licensing and Collaboration Revenue The Company analyzes license and collaboration arrangements pursuant to FASB ASC Topic 808, Collaborative Arrangement Guidance and Considerations, (“ASC 808”) to assess whether such arrangements, or transactions between arrangement participants, involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities or are more akin to a vendor-customer relationship. In making this evaluation, the Company considers whether the activities of the collaboration are considered to be distinct and deemed to be within the scope of the collaborative arrangement guidance or if they are more reflective of a vendor-customer relationship and, therefore, within the scope of ASC 606. This assessment is performed throughout the life of the arrangement based on changes in the responsibilities of all parties in the arrangement. For elements of collaboration arrangements that are not accounted for pursuant to guidance in ASC 606, an appropriate recognition method is determined and applied consistently, generally by analogy to the revenue from contracts with customers guidance. Amounts related to transactions with a counterparty in a collaborative arrangement that is not a customer are presented as collaboration revenue and in a separate line item from revenue recognized from contracts with customers, if any, in the Company’s consolidated statements of operations. Pursuant to ASC 606, for arrangements or transactions between arrangement participants determined to be within the scope of the contracts with customers guidance, the Company performs the five step process discussed above to determine the appropriate amount of revenue to be recognized as the Company fulfills its obligations. The Company evaluates the performance obligations promised in the contract that are based on goods and services that will be transferred to the customer and determine whether those obligations are both (i) capable of being distinct and (ii) distinct in the context of the contract. Goods or services that meet these criteria are considered distinct performance obligations . Revenue is recognized when, or as, the Company satisfies a performance obligation by transferring a promised good or service to a customer. An asset is transferred when, or as, the customer obtains control of that asset. For performance obligations that are satisfied over time, the Company recognizes revenue using an input or output measure of progress that best depicts the satisfaction of the relevant performance obligation. After contract inception, the transaction price is reassessed at every period end and updated for changes such as resolution of uncertain events. Any change in the overall transaction price is allocated to the performance obligations on the same methodology as at contract inception. See Note 13, License and Collaboration Agreements, for further discussion related to the Collaboration and License Agreement with Sobi
Cost of Research Collaboration Arrangements	Cost of Research Collaboration Arrangements The Company analyzes research collaboration arrangements pursuant to ASC 808 to assess whether such arrangements, or transactions between arrangement participants, involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities. If e ach party is actively participating in this activity and exposed to significant risks and rewards related to the activity through each party’s costs will be accounted for under ASC 808 . Since ASC 808 does not provide recognition guidance, the Company refers to the guidance under FASB ASC 730, Research and Development, ( “ASC 730”) to arrangements involving payments by the Company . ASC 730 requires the Company to recognize research and developments costs as expense as incurred since there is no alternative use. The Company paid a $50.0 million up-front non-refundable payment to Beam Therapeutics, Inc. (“Beam”), in July 2021, which was recorded as a cost of research collaboration in research and development expenses during the nine months ended September 30, 2021. The Company did not record any cost of research collaboration in research and development expenses for the three months ended September 30, 2021. See Note 13 License and Collaboration Agreements for further discussion related to the
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk are primarily cash, cash equivalents, restricted cash, marketable securities and account receivables. The Company’s cash, cash equivalents, restricted cash and marketable securities are concentrated at financial institutions that management believes are creditworthy. Marketable securities consist of treasury notes and certificates of deposit. The Company's investment policy includes guidelines on the quality of the institutions and financial instruments and defines allowable investments that the Company believes minimizes the exposure to concentrations of credit risk. The Company has entered into distribution agreements with a limited number of SPs and SDs, and all of the Company’s product sales will be to these customers. For the quarter ended September 30, 2021, a small number of customers represented all of the Company’s product revenue and accounts receivable balance at September 30, 2021. The Company The Company does not currently have any of its own manufacturing facilities, and therefore it depends on an outsourced manufacturing strategy for the production of EMPAVELI for commercial use and for the production of its product candidates for clinical trials. The Company has contracts in place with one third-party manufacturer of commercial drug product and one third-party manufacturer of the drug substance that is approved for the production of EMPAVELI active pharmaceutical ingredient (API). Although there are potential sources of supply other than the Company’s existing suppliers, any new supplier would be required to qualify under applicable regulatory requirements.
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 7, Long-term Debt, Note 9, Marketable Securities, and Note 11, Fair Value Measurements, include cash and cash equivalents, accounts receivable, other receivables, accounts payable and accrued liabilities. Management believes that the carrying amounts of certain cash and cash equivalents, accounts receivable, other receivables, accounts payable and accrued expenses approximate the fair value due to the short-term nature of those instruments.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents are defined as cash in banks and investment instruments having maturities of three months or less from their acquisition date. The carrying amounts reported in the condensed consolidated balance sheets for certain cash and cash equivalents are valued at cost, which approximates their fair value. See Note 11, Fair Value Measurements, for additional information.
Restricted Cash	Restricted Cash The Company is contingently liable under unused letters of credit with a bank, related to the Company’s customs import bond and facility lease agreements of $1.6 million and $1.3 million as of September 30, 2021 and December 31, 2020, respectively. The Company records as restricted cash the collateral used to secure these letters of credit.
Accounts Receivable	Accounts Receivable The Company’s accounts receivable primarily arise from product sales. They are generally stated at the invoiced amount and do not bear interest. The Company recognizes revenue from product sales at the net sales price which includes estimates of variable consideration for which reserves are established and reflects each of these as a reduction to the revenue. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which the Company is entitled based on the terms of the contract. The amount of variable consideration that is included in the transaction price may be constrained. The accounts receivable from product sales represents receivables due from the Company’s SPs or SDs. The Company has had no historical write-offs of its accounts receivable and its payment terms are generally 30-65 days. The Company monitors the financial performance and creditworthiness of its customers and provides reserves against trade receivables for expected credit losses that may result from a customer’s inability to pay. Amounts determined to be uncollectible are written-off against the established reserve. As of September 3 0 , 2021, the credit profiles for the Company’s customers were deemed to be in good standing and an allowance for credit losses was not considered necessary .
Inventory	Inventory Inventory is recorded at the lower of cost or net realizable value, with cost determined on a first-in, first-out basis. Inventory costs include third-party contract manufacturing, third-party packaging services, and freight. The Company primarily uses actual costs to determine the cost basis for its inventory. The Company periodically reviews its inventories to identify obsolete, slow moving, excess or otherwise unsaleable items. The determination of whether inventory costs will be realizable requires estimates by management. The Company does not have any obsolete inventory as of September 30, 2021. Prior to regulatory approval of its product candidates, the Company expenses costs associated with the manufacture of its product candidates to research and development expense unless the Company is reasonably certain such costs have future commercial use and net realizable value. When the Company believes regulatory approval and subsequent commercialization of our product candidates is probable, and the Company also expects future Prior to receiving FDA approval for EMPAVELI on May 14, 2021, the Company included in research and development expense the costs associated with the manufacture of EMPAVELI inventory to be sold upon commercialization. As a result, the manufacturing costs related to the EMPAVELI inventory build-up incurred before FDA approval were already expensed in a prior period and are therefore excluded from the cost of goods sold for the three and nine months ended September 30, 2021.
Foreign Currency	Foreign Currency The financial position and results of operations of the Company's Australian, Irish and German subsidiaries are measured using the foreign subsidiary's local currency. Revenues and expenses of the subsidiaries have been translated into U.S. dollars at average exchange rates prevailing during the respective periods. Assets and liabilities have been translated at the rates of exchange on the balance sheet date. The resulting translation gain and loss adjustments are recorded directly as a separate component of stockholders’ equity .

Prepaid Assets and Accrued Ex_2

Prepaid Assets and Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2021
Prepaid Assets And Accrued Expenses [Abstract]
Schedule of Accrued Expenses	Accrued expenses are as follows (in thousands): September 30, December 31, 2021 2020 Accrued research and development $ 28,670 $ 47,879 Accrued license fee — 25,050 Accrued payroll liabilities 27,124 22,896 Other 14,053 16,110 Total $ 69,847 $ 111,935

Development Derivative Liabil_2

Development Derivative Liability (Tables)	9 Months Ended
	Sep. 30, 2021
Research And Development [Abstract]
Schedule of Development Derivative Liability	The following table presents a rollforward of the development derivative liability (in thousands): For the Nine Months Ended September 30, 2021 2020 Balance at fair market value, January 1, $ 257,868 $ 134,839 Amounts received under the SFJ Agreement and SFJ Amendment — 20,000 Loss recorded in loss from remeasurement of development derivative liability 17,084 68,406 Balance at fair market value, March 31, 274,952 223,245 Amounts repaid under the SFJ Agreement and SFJ Amendment (4,000 ) — Loss/(gain) recorded in loss from remeasurement of development derivative liability 21,180 (2,770 ) Balance at fair market value, June 30, 292,132 220,475 Amounts received under the SFJ agreement and SFJ amendment — — Loss/(gain) recorded in loss from remeasurement of development derivative liability 4,219 (2,697 ) Balance at fair market value, September 30, $ 296,351 $ 217,778

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Schedule of Additional Information Related to Operating Lease Assets and Liabilities	Additional information related to the operating lease assets and liabilities is as follows (in thousands): September 30, December 31, 2021 2020 Operating Lease Assets $ 20,930 $ 17,719 Operating Lease Liabilities $ 22,222 $ 18,902 Weighted Average Remaining Term in years 4.87 4.66 Weighted Average discount rate used to measure outstanding lease liabilities 7.71 % 7.74 %
Supplemental Cash Flow Information Related to Operating Leases	Supplemental cash flow information related to operating leases for the nine months ended September 30 is as follows (in thousands): 2021 2020 Operating cash flows for operating leases $ 4,476 $ 3,322 Operating lease assets obtained in exchange for lease obligations $ 5,675 $ 6,664
Maturities of Operating Lease Liabilities	The maturities of the Company’s operating lease liabilities as of September 30, 2021 are as follows (in thousands): 2021 $ 1,436 2022 5,561 2023 5,625 2024 4,862 2025 and thereafter 9,261 Total future minimum lease payments less 26,745 Imputed interest (4,523 ) Total operating lease liabilities $ 22,222

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2021
Investments Debt And Equity Securities [Abstract]
Schedule of Amortized Cost, Gross Unrealized Holding Losses and Fair Value of Available-for-Sale Debt Securities by Type of Security	The amortized cost, gross unrealized holding losses and fair value of available-for-sale debt securities by type of security as of September 30, 2021 and December 31, 2020 were as follows (in thousands): As of September 30, 2021 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Fair Value U.S. Government-related obligations $ 146,555 $ 11 $ — $ 146,566 As of December 31, 2020 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Fair Value U.S. Government-related obligations $ 311,877 $ 11 $ (19 ) $ 311,869

Other Comprehensive Income an_2

Other Comprehensive Income and Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Summary of Changes in Accumulated Other Comprehensive Income/(Loss), by Component	The following tables summarize the changes in accumulated other comprehensive income/(loss), by component for the nine months ended September 30, 2021 and 2020 (in thousands): Unrealized Gains (Losses) from Marketable Securities Foreign Currency Translation Adjustment Total Accumulated Other Comprehensive Income (Loss) Balances, December 31, 2020 $ (8 ) $ (109 ) $ (117 ) Net other comprehensive income (loss) 79 (1,582 ) (1,503 ) Balances, March 31, 2021 71 (1,691 ) (1,620 ) Net other comprehensive income (loss) (35 ) (174 ) (209 ) Balances, June 30, 2021 36 (1,865 ) (1,829 ) Net other comprehensive income (loss) (25 ) (156 ) (181 ) Balances, September 30, 2021 $ 11 $ (2,021 ) $ (2,010 ) 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 Net other comprehensive income (loss) (430 ) (1,658 ) (2,088 ) Balances, September 30, 2020 $ 122 $ (1,881 ) $ (1,759 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value, Nonrecurring [Member]
Schedule of Financial Instruments and the Related Fair Value Hierarchy of the Valuation Techniques Utilized	The following table presents the fair value of financial instruments recorded originally at amortized cost or fair value and not remeasured on a recurring basis (in thousands): September 30, 2021 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Cash and cash equivalents: Money market funds $ 254,088 $ — $ — $ 254,088 Total Financial Assets $ 254,088 $ — $ — $ 254,088 December 31, 2020 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Cash and cash equivalents Money market funds $ 427,515 $ — $ — $ 427,515 Bank certificates of deposit 43,577 — — 43,577 Total Financial Assets $ 471,092 $ — $ — $ 471,092 * The convertible notes were measured and recognized at fair value on the consolidated balance sheet at inception.
Fair Value, Recurring [Member]
Schedule of Financial Instruments and the Related Fair Value Hierarchy of the Valuation Techniques Utilized	The following table presents the fair value of financial instruments recorded at fair value at inception and remeasured on a recurring basis (in thousands): September 30, 2021 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Marketable securities: US government obligations $ 146,566 — — $ 146,566 Total Financial Assets $ 146,566 $ — $ — $ 146,566 Financial Liabilities: Development derivative liability Development derivative liability $ — $ — $ 296,351 $ 296,351 Total Financial Liabilities $ — $ — $ 296,351 $ 296,351 December 31, 2020 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Cash and cash equivalents US government obligations $ 89,990 $ — $ — $ 89,990 Marketable securities: US government obligations 311,869 — — 311,869 Total Financial Assets $ 401,859 $ — $ — $ 401,859 Financial Liabilities: Development derivative liability Development derivative liability $ — $ — $ 257,868 $ 257,868 Total Financial Liabilities $ — $ — $ 257,868 $ 257,868

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Summary of Shares Outstanding that were Excluded from Calculation of Diluted Net Loss Per Share	Convertible notes and shares outstanding presented below were excluded from the calculation of diluted net loss per share, prior to the use of the treasury stock method, as their effect is anti-dilutive (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2021 2020 2021 2020 Convertible notes 4,884 13,177 4,884 13,177 Common stock options 12,954 12,174 12,954 12,174 Restricted stock units 1,071 433 1,071 433 Total 18,909 25,784 18,909 25,784

Nature of Organization and Op_2

Nature of Organization and Operations - Additional Information (Detail) - USD ($) $ in Thousands	Jan. 01, 2021	Jul. 31, 2021	Jan. 31, 2021	Sep. 30, 2021	Sep. 30, 2021
Nature Of Organization And Operations [Line Items]
Aggregate principal amount converted					$ 327,276
Total loss on conversion of debt				$ 61,102	100,589
Cash and cash equivalents and marketable securities				430,300	430,300
Convertible Senior Notes Due 2026 [Member]
Nature Of Organization And Operations [Line Items]
Aggregate principal amount converted				$ 700
Aggregate principal amount converted into shares				18,775
Convertible Senior Notes Due 2026 [Member] | Exchange Agreements [Member]
Nature Of Organization And Operations [Line Items]
Total loss on conversion of debt		$ 100,600	$ 100,600
2019 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [Member] | Exchange Agreements [Member]
Nature Of Organization And Operations [Line Items]
Increase (decrease) in net debt		(197,000)	(122,800)
Aggregate principal amount converted		$ 201,100	$ 126,100
Additional shares issued for settlement of debt issuance cost paid		78,419	69,491	78,419
Total loss on conversion of debt			$ 39,500	$ 61,100
2019 and 2020 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [Member] | Exchange Agreements [Member]
Nature Of Organization And Operations [Line Items]
Aggregate principal amount converted		$ 201,100			327,200
Total loss on conversion of debt				$ 61,100	$ 100,600
Additional shares agreed to issue for settlement of debt issuance cost paid		78,419
Common Stock [Member] | 2019 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [Member] | Exchange Agreements [Member]
Nature Of Organization And Operations [Line Items]
Aggregate principal amount converted into shares		5,992,217	3,906,869
Common Stock [Member] | 2019 and 2020 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [Member] | Exchange Agreements [Member]
Nature Of Organization And Operations [Line Items]
Aggregate principal amount converted into shares		5,992,217
ASU 2020-06 [Member]
Nature Of Organization And Operations [Line Items]
Change in accounting principle accounting standards update adopted				true	true
Change in accounting principle accounting standards update adoption date				Jan. 1, 2021	Jan. 1, 2021
Increase (decrease) in net debt	$ 149,700
Decrease in net equity	(149,700)
ASU 2020-06 [Member] | Retained Earnings [Member]
Nature Of Organization And Operations [Line Items]
Decrease in net equity	$ (16,000)

Basis of Presentation - Additio

Basis of Presentation - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended
	Jul. 31, 2021	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Cost of research collaboration			$ 50,000,000
Accounts receivable, allowance for credit losses		$ 0	0
Restricted cash		1,563,000	1,563,000	$ 1,266,000
Obsolete inventory		0	$ 0
Collaboration and License Agreement [Member] | Beam Therapeutics, Inc [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Upfront payment	$ 50,000,000
Collaboration and License Agreement [Member] | Research and Development Expense [Member] | Beam Therapeutics, Inc [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Cost of research collaboration		$ 0

Product Revenues, Accounts Re_2

Product Revenues, Accounts Receivable, and Reserves for Product Sales - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Revenue	$ 5,650	$ 646	$ 6,273	$ 646
Accounts receivable	3,522		3,522
Accrued Expenses [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Product sales reserves	300		300
Product [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Revenue	$ 5,314	$ 0	$ 5,937	$ 0

Inventory - Additional Informat

Inventory - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Inventory, Semi-finished goods	$ 1,400
Inventory, Finished goods	300
Inventory	$ 1,677	$ 0

Prepaid Assets and Accrued Ex_3

Prepaid Assets and Accrued Expenses - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Prepaid Assets And Accrued Expenses [Abstract]
Prepaid research and development	$ 12	$ 8

Prepaid Assets and Accrued Ex_4

Prepaid Assets and Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Prepaid Assets And Accrued Expenses [Abstract]
Accrued research and development	$ 28,670	$ 47,879
Accrued license fee		25,050
Accrued payroll liabilities	27,124	22,896
Other	14,053	16,110
Total	$ 69,847	$ 111,935

Development Derivative Liabil_3

Development Derivative Liability - Additional Information (Detail)	Feb. 28, 2019USD ($)Installment	Sep. 30, 2021USD ($)	Jun. 30, 2021USD ($)	Mar. 31, 2021USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Jun. 07, 2019USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Gain (loss) from remeasurement of development derivative liability		$ (4,219,000)	$ (21,180,000)	$ (17,084,000)	$ 2,697,000	$ 2,770,000	$ (68,406,000)	$ (42,483,000)	$ (62,939,000)
Development derivative liability		281,017,000						281,017,000		$ 253,638,000
Current portion of development derivative liability		15,334,000						$ 15,334,000		$ 4,230,000
Level 3 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Implied cost of borrowing discount rates								11.90%
SFJ Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from SFJ agreement	$ 60,000,000							$ 140,000,000	20,000,000
Additional funding amount upon achievement of development milestones	$ 60,000,000
Number of milestone payments | Installment	3
Development funding for minimum period of operating expense	10 months
Increase in additional funding for development costs											$ 20,000,000
Payment made under agreement								4,000,000
Gain (loss) from remeasurement of development derivative liability		(4,200,000)			$ 2,700,000			(42,500,000)	$ (62,900,000)
Development derivative liability		296,300,000						296,300,000
Current portion of development derivative liability		$ 15,300,000						$ 15,300,000
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] | Regulatory Approval Granted US Food and Drug Administration [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Obligated to pay initial payment	$ 4,000,000
Number of additional annual payments | Installment	6
SFJ Agreement [Member] | Regulatory Approval Granted US Food and Drug Administration [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate amount of additional annual payments	$ 226,000,000
SFJ Agreement [Member] | Regulatory Approval Granted by EMA [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of additional annual payments | Installment	6
SFJ Agreement [Member] | Regulatory Approval Granted by EMA [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Obligated to pay initial payment	$ 5,000,000
Aggregate amount of additional annual payments	$ 226,000,000

Development Derivative Liabil_4

Development Derivative Liability - Schedule of Development Derivative Liability (Detail) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance at fair market value	$ 292,132	$ 274,952	$ 257,868	$ 220,475	$ 223,245	$ 134,839	$ 257,868	$ 134,839
Amounts received under the SFJ Agreement and SFJ Amendment		(4,000)				20,000
(Gain)/loss recorded in loss from remeasurement of development derivative liability	4,219	21,180	17,084	(2,697)	(2,770)	68,406	42,483	62,939
Balance at fair market value	$ 296,351	$ 292,132	$ 274,952	$ 217,778	$ 220,475	$ 223,245	$ 296,351	$ 217,778

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Detail)	Jan. 01, 2021USD ($)	May 12, 2020USD ($)	Sep. 16, 2019USD ($)	Jul. 31, 2021USD ($)shares	Jan. 31, 2021USD ($)shares	Sep. 30, 2021USD ($)$ / sharesshares	Mar. 31, 2021shares	Sep. 30, 2021USD ($)d$ / shares	Dec. 31, 2020USD ($)	May 06, 2020CounterParty$ / shares	Sep. 11, 2019USD ($)CounterParty$ / shares
Debt Instrument [Line Items]
Aggregate principal amount converted								$ 327,276,000
Loss on conversion of debt						$ 61,102,000		100,589,000
Forfeiture of accrued interest in exchange of convertible notes								$ 4,171,000
ASU 2020-06 [Member]
Debt Instrument [Line Items]
Change in accounting principle accounting standards update adopted						true		true
Change in accounting principle accounting standards update adoption date						Jan. 1, 2021		Jan. 1, 2021
Increase (decrease) in net debt	$ 149,700,000
Decrease in net equity	149,700,000
Convertible notes	149,700,000
Non-cash interest expense	17,100,000
Amortization of debt issuance costs	1,100,000
Common Stock [Member]
Debt Instrument [Line Items]
Shares issued | shares						6,071	3,976
2019 Convertible Notes [Member]
Debt Instrument [Line Items]
Premium paid for capped call transactions								$ 28,400,000
2019 Convertible Notes [Member] | ASU 2020-06 [Member]
Debt Instrument [Line Items]
Debt issuance costs	2,400,000
Convertible notes	74,900,000
2020 Convertible Notes [Member]
Debt Instrument [Line Items]
Premium paid for capped call transactions								$ 43,100,000
2020 Convertible Notes [Member] | ASU 2020-06 [Member]
Debt Instrument [Line Items]
Debt issuance costs	2,300,000
Convertible notes	$ 95,500,000
Capped Call Transactions [Member]
Debt Instrument [Line Items]
Number of counterparties | CounterParty										2	2
Initial conversion price | $ / shares										$ 39.4625	$ 39.4625
Initial cap price | $ / shares											$ 63.14
Convertible Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt instrument, stated percentage			3.50%
Debt instrument, due and payment description								The Convertible Notes are senior unsecured obligations of the Company and bear interest at a rate of 3.5% per year payable semiannually in arrears on March 15 and September 15 of each year, beginning on March 15, 2020.
Debt instrument, frequency of periodic payment								semiannually
Maturity date			Sep. 15, 2026
Threshold trading days | d								20
Threshold consecutive trading days | d								30
Threshold percentage of stock price trigger								130.00%
Redemption period, start date								Sep. 20, 2023
Redemption price, percentage								100.00%
Amortization of debt issuance costs						$ 200,000		$ 800,000
Aggregate principal amount converted						$ 700,000
Aggregate principal amount converted into shares | shares						18,775
Debt interest expense						$ 2,300,000		10,200,000
Accrued semi annual coupon payable						2,100,000		9,400,000
Debt issuance costs gross						3,100,000		3,100,000
Long-term debt						$ 189,600,000		$ 189,600,000	$ 358,800,000
Convertible Senior Notes Due 2026 [Member] | Exchange Agreements [Member]
Debt Instrument [Line Items]
Loss on conversion of debt				$ 100,600,000	$ 100,600,000
Convertible Senior Notes Due 2026 [Member] | Prior to March 15, 2026 Convertible [Member]
Debt Instrument [Line Items]
Threshold trading days | d								20
Threshold consecutive trading days | d								30
Threshold percentage of stock price trigger								130.00%
Trading price per principal amount								$ 1,000
Convertible Senior Notes Due 2026 [Member] | Prior to March 15, 2026 Convertible [Member] | Maximum [Member]
Debt Instrument [Line Items]
Threshold percentage of stock price trigger								98.00%
Convertible Senior Notes Due 2026 [Member] | Common Stock [Member]
Debt Instrument [Line Items]
Terms of conversion								The Convertible Notes are convertible into shares of the Company’s common stock at an initial conversion rate of 25.3405 shares per $1,000 principal amount of Convertible Notes (equivalent to an initial conversion price of approximately $39.4625 per share of common stock).
Conversion ratio								0.0253405
Conversion price | $ / shares						$ 39.4625		$ 39.4625
Convertible Senior Notes Due 2026 [Member] | 2019 Convertible Notes [Member]
Debt Instrument [Line Items]
Net proceeds from the sale of the notes			$ 212,900,000
Payment of convertible debt discounts and commissions			6,600,000
Payment of convertible debt offering expenses			500,000
Payments of transactions cost			28,400,000
Debt instrument effective interest rate											10.50%
Debt instrument convertible carrying amount of liability component											$ 145,100,000
Debt discount											74,900,000
Debt issuance costs											7,100,000
Convertible Senior Notes Due 2026 [Member] | 2019 Convertible Notes [Member] | Exchange Agreements [Member]
Debt Instrument [Line Items]
Conversion ratio				0.0253405	0.0253405
Debt issuance costs				$ 4,100,000	$ 3,300,000
Increase (decrease) in net debt				(197,000,000)	(122,800,000)
Aggregate principal amount converted				$ 201,100,000	$ 126,100,000
Increase in shares outstanding | shares				5,992,217	3,906,869
Shares issued | shares				5,097,166	3,196,172
Additional shares issued | shares				895,051	710,697
Additional shares issued for settlement of debt issuance cost paid | shares				78,419	69,491	78,419
Loss on conversion of debt					$ 39,500,000	$ 61,100,000
Loss on conversion of debt related to additional shares issued					36,400,000	55,900,000
Additional amount issued in payment of issuance costs					3,100,000	5,200,000
Forfeiture of accrued interest in exchange of convertible notes					$ 1,700,000
Convertible Senior Notes Due 2026 [Member] | 2019 Convertible Notes [Member] | Common Stock [Member] | Exchange Agreements [Member]
Debt Instrument [Line Items]
Aggregate principal amount converted into shares | shares				5,992,217	3,906,869
Convertible Senior Notes Due 2026 [Member] | 2019 Convertible Notes [Member] | Liability Component [Member]
Debt Instrument [Line Items]
Debt issuance costs											4,700,000
Convertible Senior Notes Due 2026 [Member] | 2019 Convertible Notes [Member] | Equity Component [Member]
Debt Instrument [Line Items]
Debt issuance costs											$ 2,400,000
Convertible Senior Notes Due 2026 [Member] | 2020 Convertible Notes [Member]
Debt Instrument [Line Items]
Net proceeds from the sale of the notes		$ 322,900,000
Payment of convertible debt discounts and commissions		5,700,000
Payment of convertible debt offering expenses		300,000
Payments of transactions cost		$ 43,100,000
Debt instrument effective interest rate		10.50%
Debt instrument convertible carrying amount of liability component		$ 204,500,000
Debt discount		95,500,000
Debt issuance costs		6,000,000
Convertible Senior Notes Due 2026 [Member] | 2020 Convertible Notes [Member] | Exchange Agreements [Member]
Debt Instrument [Line Items]
Aggregate principal amount converted								$ 327,200,000
Convertible Senior Notes Due 2026 [Member] | 2020 Convertible Notes [Member] | Liability Component [Member]
Debt Instrument [Line Items]
Debt issuance costs		3,700,000
Convertible Senior Notes Due 2026 [Member] | 2020 Convertible Notes [Member] | Equity Component [Member]
Debt Instrument [Line Items]
Debt issuance costs		2,300,000
Convertible Senior Notes Due 2026 [Member] | 2019 and 2020 Convertible Notes [Member] | Exchange Agreements [Member]
Debt Instrument [Line Items]
Aggregate principal amount converted				$ 201,100,000				327,200,000
Loss on conversion of debt						61,100,000		$ 100,600,000
Forfeiture of accrued interest in exchange of convertible notes						$ 2,500,000
Convertible Senior Notes Due 2026 [Member] | 2019 and 2020 Convertible Notes [Member] | Common Stock [Member] | Exchange Agreements [Member]
Debt Instrument [Line Items]
Aggregate principal amount converted into shares | shares				5,992,217
Convertible Senior Notes Due 2026 [Member] | Private Offering [Member] | 2019 Convertible Notes [Member]
Debt Instrument [Line Items]
Principal amount			$ 220,000,000
Convertible Senior Notes Due 2026 [Member] | Private Offering [Member] | 2020 Convertible Notes [Member]
Debt Instrument [Line Items]
Principal amount		$ 300,000,000

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Lessee Lease Description [Line Items]
Operating lease description			The Company enters into lease agreements with terms generally ranging from 2-7 years. Some of the Company’s lease agreements include Company options to extend the lease on a month-to-month basis or for set periods for up to five years. Many of these leases also include options to terminate the leases within one year or per other contractual terms. Renewal and termination options were generally not included in the lease term for the Company’s existing operating leases.
Operating lease, existence of option to extend			true
Operating lease maximum term of options to terminate lease			1 year
Operating lease expense	$ 1.4	$ 1.1	$ 4.2	$ 3.1
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

Leases - Schedule of Additional

Leases - Schedule of Additional Information Related to Operating Lease Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases [Abstract]
Operating Lease Assets	$ 20,930	$ 17,719
Operating Lease Liabilities	$ 22,222	$ 18,902
Weighted Average Remaining Term in years	4 years 10 months 13 days	4 years 7 months 28 days
Weighted Average discount rate used to measure outstanding lease liabilities	7.71%	7.74%

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information Related to Operating Leases (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating cash flows for operating leases	$ 4,476	$ 3,322
Operating lease assets obtained in exchange for lease obligations	$ 5,675	$ 6,664

Leases - Maturities of Operatin

Leases - Maturities of Operating Lease Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases [Abstract]
2021	$ 1,436
2022	5,561
2023	5,625
2024	4,862
2025 and thereafter	9,261
Total future minimum lease payments less	26,745
Imputed interest	(4,523)
Operating Lease Liabilities	$ 22,222	$ 18,902

Marketable Securities - Schedul

Marketable Securities - Schedule of Amortized Cost, Gross Unrealized Holding Losses and Fair Value of Available-for-Sale Debt Securities by Type of Security (Detail) - U.S. Government-Related Obligations [Member] - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Available for sale securities:
Amortized Cost	$ 146,555	$ 311,877
Gross Unrealized Holding Gains	11	11
Gross Unrealized Holding Losses		(19)
Fair Value	$ 146,566	$ 311,869

Other Comprehensive Income an_3

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
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ (141,493)	$ 51,658	$ 204,557	$ 232,064	$ 258,997	$ 34,229
Net other comprehensive income (loss)	(181)	(209)	(1,503)	(2,088)	(681)	1,164
Ending balance	(57,325)	(141,493)	51,658	105,840	232,064	258,997
Unrealized Gains (Losses) from Marketable Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	36	71	(8)	552	1,394
Net other comprehensive income (loss)	(25)	(35)	79	(430)	(842)	1,394
Ending balance	11	36	71	122	552	1,394
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(1,865)	(1,691)	(109)	(223)	(384)	(154)
Net other comprehensive income (loss)	(156)	(174)	(1,582)	(1,658)	161	(230)
Ending balance	(2,021)	(1,865)	(1,691)	(1,881)	(223)	(384)
Total Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(1,829)	(1,620)	(117)	329	1,010	(154)
Ending balance	$ (2,010)	$ (1,829)	$ (1,620)	$ (1,759)	$ 329	$ 1,010

Fair Value Measurements - Sched

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	Sep. 30, 2021	Dec. 31, 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 254,088	$ 471,092
Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	254,088	427,515
Bank Certificates of Deposit [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets		43,577
Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	254,088	471,092
Level 1 [Member] | Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 254,088	427,515
Level 1 [Member] | Bank Certificates of Deposit [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets		$ 43,577

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Level 1 [Member] | Convertible Senior Notes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Convertible notes	$ 241.2
Convertible notes, interest rate	3.50%
Level 2 [Member] | Convertible Senior Notes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Convertible notes		$ 676.2
Convertible notes, interest rate		3.50%
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Percentage of cost of borrowing	11.90%
Level 3 [Member] | SFJ Agreement [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Percentage of cost of borrowing	8.00%

Fair Value Measurements - Sch_2

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	Sep. 30, 2021	Dec. 31, 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 146,566	$ 401,859
Total Financial Liabilities	296,351	257,868
Cash and Cash Equivalents [Member] | US Government Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets		89,990
Marketable Securities [Member] | US Government Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	146,566	311,869
Development Derivative Liability [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	296,351	257,868
Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	146,566	401,859
Level 1 [Member] | Cash and Cash Equivalents [Member] | US Government Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets		89,990
Level 1 [Member] | Marketable Securities [Member] | US Government Obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	146,566	311,869
Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	296,351	257,868
Level 3 [Member] | Development Derivative Liability [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Liabilities	$ 296,351	$ 257,868

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Expense Benefit Continuing Operations [Abstract]
Minimum percentage of tax position likelihood of being realized upon examination by taxing authorities			50.00%
Unrecognized income tax benefits	$ 0		$ 0
Current income tax expense or benefit	0	$ 0	0	$ 0
Deferred income tax expense or benefit	$ 0	$ 0	$ 0	$ 0

License and Collaboration Agr_2

License and Collaboration Agreements - Additional Information (Detail)	Nov. 30, 2020USD ($)	Oct. 27, 2020USD ($)	Aug. 31, 2021USD ($)	Jun. 30, 2021Program	Jan. 31, 2021USD ($)	Sep. 30, 2021USD ($)License	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)License	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Jul. 31, 2021USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue						$ 5,650,000	$ 646,000	$ 6,273,000	$ 646,000
Contract research and development expense						6,400,000		23,600,000
Contract research and development receivable										$ 43,000,000
Contract research and development current						20,000,000		20,000,000		25,000,000
Contract research and development long-term assets						21,600,000		21,600,000		18,000,000
Accrued expenses						69,847,000		69,847,000		111,935,000
Cost of research collaboration								50,000,000
Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments								$ 15,000,000
Payment of royalty fees								6.00%
Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of royalty fees								3.00%
Swedish Orphan Biovitrum AB (Publ) [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development cost reimbursement		$ 80,000,000
Non-refundable Upfront Payment		250,000,000
Collaboration and License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development cost reimbursement commitment										80,000,000
Collaboration and License Agreement [Member] | License [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment										250,000,000
Collaboration and License Agreement [Member] | Swedish Orphan Biovitrum AB (Publ) [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment		250,000,000
Milestone payment achieved		50,000,000
Development cost reimbursement		$ 80,000,000
Royalties entitled to receive after first commercial sale of applicable licensed product period		10 years
Contract research and development reimbursement commitment								$ 80,000,000
Contract research and development receivable						41,600,000		41,600,000
Proceeds from contract research and development					$ 25,000,000
Collaboration and License Agreement [Member] | Swedish Orphan Biovitrum AB (Publ) [Member] | License [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue						0		0
Collaboration and License Agreement [Member] | Swedish Orphan Biovitrum AB (Publ) [Member] | ASC Topic 808
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment	$ 250,000,000
Development cost reimbursement		$ 80,000,000
Collaboration and License Agreement [Member] | Swedish Orphan Biovitrum AB (Publ) [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate milestone payments upon achievement of specified one-time regulatory and commercial milestone events		915,000,000
Collaboration and License Agreement [Member] | Swedish Orphan Biovitrum AB (Publ) [Member] | Maximum [Member] | ASC Topic 808
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate milestone payments upon achievement of specified one-time regulatory and commercial milestone events		$ 915,000,000
University of Pennsylvania [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Annual maintenance fees								100,000
Development milestone achievement			$ 1,000,000
University of Pennsylvania [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate milestones payments						$ 3,200,000		3,200,000
Milestone payments based on annual sales milestones								5,000,000
2010 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Annual maintenance fees								$ 100,000
Number of licensed products | License						2		2
2010 License Agreement [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate milestones payments						$ 1,700,000		$ 1,700,000
Milestone payments based on annual sales milestones								2,500,000
Sobi Agreement and Another Licensing Transaction [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sublicense fee owed										25,000,000
Accrued expenses										25,000,000
License fees										$ 25,000,000
Research Collaboration Agreement [Member] | Beam [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement term				5 years
Number of research programs | Program				6
Up-front non-refundable payment						50,000,000		50,000,000			$ 50,000,000
Up-front payment on first anniversary of agreement on June 30, 2022						25,000,000		25,000,000
Unrecognized upfront payment						25,000,000		$ 25,000,000
Collaboration agreement maximum extendable term				2 years
Research Collaboration Agreement [Member] | Beam [Member] | Research and Development Expense [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cost of research collaboration						$ 0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Nov. 08, 2021	Sep. 30, 2021
Commitments And Contingencies [Line Items]
Estimated termination costs and other fees		$ 2,400,000
Incurred any cost to defend lawsuits or settle claims		$ 0
Vehicles [Member]
Commitments And Contingencies [Line Items]
Operating lease, term of contract		36 months
Maximum [Member]
Commitments And Contingencies [Line Items]
Operating lease, term of contract		7 years
Minimum [Member]
Commitments And Contingencies [Line Items]
Operating lease, term of contract		2 years
Through September 2022 [Member] | Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Non-cancellable purchase commitments	$ 65,200,000
Through December 2023 [Member] | Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Non-cancellable purchase commitments	37,000,000
Through December 2023 [Member] | Subsequent Event [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Non-cancellable purchase commitments costs	19,700,000
Through September 2023 [Member] | Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Non-cancellable purchase commitments	37,000,000
Non-cancellable purchase commitments costs	$ 12,800,000

Net Loss per Share - Summary of

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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	18,909	25,784	18,909	25,784
Convertible Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	4,884	13,177	4,884	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	12,954	12,174	12,954	12,174
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	1,071	433	1,071	433