Apellis Pharmaceuticals (APLS) 10-Q 5 Nov 24 2024 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2024	Oct. 29, 2024
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2024
Document Fiscal Year Focus	2024
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		124,393,017
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, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 396,864	$ 351,185
Accounts receivable, net	279,011	206,442
Inventory	121,058	146,362
Prepaid assets	23,809	38,820
Restricted cash	1,373	1,114
Other current assets	11,782	22,408
Total current assets	833,897	766,331
Non-current assets:
Right-of-use assets	17,060	16,745
Property and equipment, net	3,379	4,345
Long-term inventory	46,080
Other assets	1,450	1,309
Total assets	901,866	788,730
Current liabilities:
Accounts payable	42,730	37,516
Accrued expenses	139,835	127,806
Current portion of development liability		75,830
Current portion of lease liabilities	6,792	6,441
Deferred revenue	1,903
Total current liabilities	191,260	247,593
Long-term liabilities:
Long-term development liability		239,817
Long-term credit facility	358,982
Convertible senior notes	93,263	93,033
Lease liabilities	11,411	11,454
Other liabilities	9,829	2,312
Total liabilities	664,745	594,209
Commitments and contingencies (Note 13)
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized, and zero shares issued and outstanding at September 30, 2024 and December 31, 2023	0	0
Common stock, $0.0001 par value; 200,000 shares authorized at September 30, 2024 and December 31, 2023; 122,069 shares issued and outstanding at September 30, 2024, and 119,556 shares issued and outstanding at December 31, 2023	12	12
Additional paid-in capital	3,239,262	3,035,539
Accumulated other comprehensive loss	(3,140)	(3,542)
Accumulated deficit	(2,999,013)	(2,837,488)
Total stockholders' equity	237,121	194,521
Total liabilities and stockholders' equity	$ 901,866	$ 788,730

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2024	Dec. 31, 2023
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	122,069,000	119,556,000
Common stock, outstanding	122,069,000	119,556,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Revenue:
Revenue	$ 196,830	$ 110,399	$ 568,839	$ 250,214
Operating expenses:
Cost of sales	33,557	22,410	76,867	38,598
Research and development	88,569	79,421	251,216	285,105
Selling, general and administrative	121,984	145,648	379,571	359,114
Total operating expenses:	244,110	247,479	707,654	682,817
Net operating loss	(47,280)	(137,080)	(138,815)	(432,603)
Loss on extinguishment of development liability			(1,949)
Interest income	2,889	4,989	9,377	16,385
Interest expense	(12,532)	(7,310)	(28,857)	(22,179)
Other income/(expense), net	70	(603)	(405)	(946)
Net loss before taxes	(56,853)	(140,004)	(160,649)	(439,343)
Income tax expense	592	233	876	709
Net loss	(57,445)	(140,237)	(161,525)	(440,052)
Other comprehensive gain/(loss):
Foreign currency translation	222	(269)	402	(190)
Total other comprehensive income	222	(269)	402	(190)
Comprehensive loss, net of tax	$ (57,223)	$ (140,506)	$ (161,123)	$ (440,242)
Net loss per common share, basic	$ (0.46)	$ (1.17)	$ (1.31)	$ (3.73)
Net loss per common share, diluted	$ (0.46)	$ (1.17)	$ (1.31)	$ (3.73)
Weighted-average number of common shares used in net loss per common share, basic	124,234	120,292	123,698	117,827
Weighted-average number of common shares used in net loss per common share, diluted	124,234	120,292	123,698	117,827
Product Revenue, Net [Member]
Revenue:
Revenue	$ 176,571	$ 99,182	$ 518,782	$ 227,626
Licensing and other revenue [Member]
Revenue:
Revenue	$ 20,259	$ 11,217	$ 50,057	$ 22,588

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2022	$ 169,872	$ 11	$ 2,479,596	$ (875)	$ (2,308,860)
Beginning balance, Shares at Dec. 31, 2022		110,772,000
Issuance of common stock and pre-funded warrants in common stock offering	384,387	$ 1	384,386
Issuance of common stock and pre-funded warrants in common stock offering, shares		4,008,000
Issuance of common stock upon exercise of stock options	17,718		17,718
Issuance of common stock upon exercise of stock options, shares		951,000
Vesting of restricted stock units, net of shares withheld for taxes	(10,999)		(10,999)
Vesting of restricted stock units, net of shares withheld for taxes. shares		448,000
Share-based compensation expense	28,823		28,823
Net loss	(177,778)				(177,778)
Foreign currency translation	100			100
Ending balance at Mar. 31, 2023	412,123	$ 12	2,899,524	(775)	(2,486,638)
Ending balance, Shares at Mar. 31, 2023		116,179,000
Beginning balance at Dec. 31, 2022	169,872	$ 11	2,479,596	(875)	(2,308,860)
Beginning balance, Shares at Dec. 31, 2022		110,772,000
Net loss	(440,052)
Foreign currency translation	(190)
Ending balance at Sep. 30, 2023	232,271	$ 12	2,982,236	(1,065)	(2,748,912)
Ending balance, Shares at Sep. 30, 2023		118,359,000
Beginning balance at Mar. 31, 2023	412,123	$ 12	2,899,524	(775)	(2,486,638)
Beginning balance, Shares at Mar. 31, 2023		116,179,000
Issuance of common stock upon exercise of stock options	22,334		22,334
Issuance of common stock upon exercise of stock options, shares		1,208,000
Vesting of restricted stock units, net of shares withheld for taxes	(27)		(27)
Vesting of restricted stock units, net of shares withheld for taxes. shares		119,000
Share-based compensation expense	29,277		29,277
Issuance of common stock to employee stock purchase plan	3,754		3,754
Issuance of common stock to employee stock purchase plan, shares		73,000
Net loss	(122,037)				(122,037)
Foreign currency translation	(21)			(21)
Ending balance at Jun. 30, 2023	345,403	$ 12	2,954,862	(796)	(2,608,675)
Ending balance, Shares at Jun. 30, 2023		117,579,000
Issuance of common stock upon exercise of stock options	5,757		5,757
Issuance of common stock upon exercise of stock options, shares		665,000
Vesting of restricted stock units, net of shares withheld for taxes	(9)		(9)
Vesting of restricted stock units, net of shares withheld for taxes. shares		115,000
Share-based compensation expense	21,626		21,626
Net loss	(140,237)				(140,237)
Foreign currency translation	(269)			(269)
Ending balance at Sep. 30, 2023	232,271	$ 12	2,982,236	(1,065)	(2,748,912)
Ending balance, Shares at Sep. 30, 2023		118,359,000
Beginning balance at Dec. 31, 2023	194,521	$ 12	3,035,539	(3,542)	(2,837,488)
Beginning balance, Shares at Dec. 31, 2023		119,556,000
Proceeds from settlement of capped call	98,763		98,763
Issuance of common stock upon exercise of stock options	9,477		9,477
Issuance of common stock upon exercise of stock options, shares		714,000
Vesting of restricted stock units, net of shares withheld for taxes	(28)		(28)
Vesting of restricted stock units, net of shares withheld for taxes. shares		997,000
Share-based compensation expense	30,349		30,349
Net loss	(66,423)				(66,423)
Foreign currency translation	17			17
Ending balance at Mar. 31, 2024	266,676	$ 12	3,174,100	(3,525)	(2,903,911)
Ending balance, Shares at Mar. 31, 2024		121,267,000
Beginning balance at Dec. 31, 2023	194,521	$ 12	3,035,539	(3,542)	(2,837,488)
Beginning balance, Shares at Dec. 31, 2023		119,556,000
Proceeds from settlement of capped call	98,763
Net loss	(161,525)
Foreign currency translation	402
Ending balance at Sep. 30, 2024	237,121	$ 12	3,239,262	(3,140)	(2,999,013)
Ending balance, Shares at Sep. 30, 2024		122,069,000
Beginning balance at Mar. 31, 2024	266,676	$ 12	3,174,100	(3,525)	(2,903,911)
Beginning balance, Shares at Mar. 31, 2024		121,267,000
Issuance of common stock upon exercise of stock options	1,962		1,962
Issuance of common stock upon exercise of stock options, shares		233,000
Vesting of restricted stock units, net of shares withheld for taxes. shares		102,000
Share-based compensation expense	29,990		29,990
Issuance of common stock to employee stock purchase plan	3,193		3,193
Issuance of common stock to employee stock purchase plan, shares		85,000
Net loss	(37,657)				(37,657)
Foreign currency translation	163			163
Ending balance at Jun. 30, 2024	264,327	$ 12	3,209,245	(3,362)	(2,941,568)
Ending balance, Shares at Jun. 30, 2024		121,687,000
Issuance of common stock upon exercise of stock options	2,556		2,556
Issuance of common stock upon exercise of stock options, shares		112,000
Vesting of restricted stock units, net of shares withheld for taxes	(14)		(14)
Vesting of restricted stock units, net of shares withheld for taxes. shares		270,000
Share-based compensation expense	27,475		27,475
Net loss	(57,445)				(57,445)
Foreign currency translation	222			222
Ending balance at Sep. 30, 2024	$ 237,121	$ 12	$ 3,239,262	$ (3,140)	$ (2,999,013)
Ending balance, Shares at Sep. 30, 2024		122,069,000

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Operating Activities
Net loss	$ (161,525)	$ (440,052)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	87,814	79,726
Loss on extinguishment of development liability	1,949
Loss on disposal of fixed assets		152
Depreciation expense	1,350	1,308
Amortization of discounts for credit facility	742
Amortization of discounts for convertible notes	230	222
Accretion of discount to development liability	8,936	19,491
Changes in operating assets and liabilities:
Accounts receivable	(72,569)	(161,542)
Inventory	(20,776)	(12,831)
Prepaid assets	15,022	(7,681)
Other current assets	10,651	5,981
Other assets	(81)	14,811
Right-of-use assets and lease liabilities	(7)	(94)
Accounts payable	(399)	(19,450)
Accrued expenses and other liabilities	19,534	23,099
Deferred revenue	1,903
Net cash used in operating activities	(107,226)	(496,860)
Investing Activities
Purchase of property and equipment	(383)	(678)
Net cash used in investing activities	(383)	(678)
Financing Activities
Proceeds from credit facility	365,454
Payment of issuance cost for credit facility	(1,589)
Repayment of development liability	(326,533)
Proceeds from settlement of capped call	98,763
Proceeds from issuance of common stock and pre-funded warrant offering, net of issuance costs		384,387
Payments for development liability		(24,500)
Proceeds from exercise of stock options	13,995	45,809
Proceeds from issuance of common stock under employee share purchase plan	3,193	3,754
Payments of employee tax withholding related to equity-based compensation	(42)	(11,038)
Net cash provided by financing activities	153,241	398,412
Effect of exchange rate changes on cash, cash equivalents and restricted cash	306	(449)
Net increase (decrease) in cash, cash equivalents and restricted cash	45,938	(99,575)
Cash, cash equivalents and restricted cash at beginning of period	352,299	553,075
Cash, cash equivalents and restricted cash at end of period	398,237	453,500
Reconciliation of cash, cash equivalents and restricted cash to the consolidated balance sheets:
Cash and cash equivalents	396,864	452,414
Restricted cash	1,373	1,086
Total cash, cash equivalents, and restricted cash	398,237	453,500
Supplemental Disclosures
Cash paid for interest	19,446	3,286
Cash paid for income taxes	600	$ 578
Issuance costs for credit facility incurred but not yet paid	$ 5,625

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (57,445)	$ (37,657)	$ (66,423)	$ (140,237)	$ (122,037)	$ (177,778)	$ (161,525)	$ (440,052)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Sep. 30, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Nature of Organization and Oper

Nature of Organization and Operations	9 Months Ended
	Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Organization and Operations	1. Nature of Organization and Operations Apellis Pharmaceuticals, Inc. (the “Company”) is a commercial-stage biopharmaceutical company focused on the discovery, development and commercialization of novel therapeutic compounds to treat diseases with high unmet needs through the inhibition of the complement system, which is an integral component of the immune system, at the level of C3, the central protein in the complement cascade. The Company was incorporated in September 2009 under the laws of the State of Delaware. The Company’s principal executive offices are located in Waltham, Massachusetts. The Company’s operations since inception have been limited to organizing and staffing the Company, acquiring rights to product candidates, business planning, raising capital, developing its product candidates, commercializing EMPAVELI (pegcetacoplan) for the treatment of paroxysmal nocturnal hemoglobinuria (“PNH”) and SYFOVRE (pegcetacoplan injection) for the treatment of geographic atrophy secondary to age-related macular degeneration (“GA”). The Company is subject to risks common in the biotechnology industry including, but not limited to, raising additional capital, development by its competitors of new technological innovations, its ability to successfully complete preclinical and clinical development of product candidates and receive timely regulatory approval of products, market acceptance of the Company’s products, protection of proprietary technology, healthcare cost containment initiatives, and compliance with governmental regulations, including those of the U.S. Food and Drug Administration (“FDA”). 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. From inception to September 30, 2024, the Company has incurred cash outflows from operations, losses from operations and had an accumulated deficit of $ 3.0 billion primarily as a result of expenses incurred through a combination of research and development activities related to the Company’s various product candidates and expenses supporting those activities. As of November 5, 2024, the date of issuance of these unaudited condensed consolidated financial statements, the Company believes that its cash and cash equivalents of $ 396.9 million as of September 30, 2024 , combined with cash anticipated to be generated from sales of EMPAVELI and SYFOVRE will be sufficient to fund its operations and capital expenditures for at least the next twelve months.

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2024
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	2. Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The 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, 2023 has been derived from audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair presentation of the Company’s financial information. The results of operations for the three and nine months ended September 30, 2024 are not necessarily indicative of the results to be expected for the year ending December 31, 2024 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, 2023 included in the Company’s Annual Report on Form 10-K filed with the SEC on February 27, 2024, as amended by Amendment No. 1 thereto filed with the SEC on February 29, 2024 (the “2023 Form 10-K”). Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: development liability, accrued expenses, prepaid expenses, convertible debt, reserves for variable consideration, reserves for excess or obsolete inventories, and income taxes. Summary of Significant Accounting Policies Reference is made to Note 2 Summary of Significant Accounting Policies in our 2023 Form 10-K for a detailed description of significant accounting policies. There have been no significant changes to our accounting policies as disclosed in our 2023 Form 10-K, except as noted below. Accounts Receivable The Company’s accounts receivable primarily arise from product sales. They are generally stated at the invoiced amount and do not bear interest. The accounts receivable from product sales represents receivables due from the Company’s SPs or SDs. The Company has had no historical write offs of its accounts receivable as of September 30, 2024 and December 31, 2023, and its payment terms are generally 30-65 days for EMPAVELI and 60-150 days for SYFOVRE. The Company monitors the financial performance and creditworthiness of its customers and provides reserves against trade receivables for expected credit losses that may result from a customer’s inability to pay. Amounts determined to be uncollectible are written-off against the established reserve. As of September 30, 2024 and December 31, 2023, 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. The Company has an agreement (the “Factoring Agreement”) to sell certain trade accounts receivable to a third-party financial institution at a discount to the invoiced amount. Under the Factoring Agreement, the maximum amount of outstanding accounts receivables sold at any time is $100.0 million. The Company accounts for the transfer of trade accounts receivable under the Factoring Agreement as a sale in accordance with ASC 860, Transfers and Servicing , because effective control and risk associated with the transferred accounts receivable is passed to the third-party. Accordingly, the Company derecognizes the sold trade accounts receivable from the consolidated balance sheets. Cash proceeds related to the accounts receivable sold are included in cash from operating activities in the consolidated statements of cash flows. Any discounts or fees incurred in connection with the sales are recorded within “Selling, general and administrative expenses" in the consolidated statements of operations and comprehensive loss. Pursuant to the Factoring Agreement, the Company performs certain collection and administrative functions for the receivable sold. The fair value of these administrative services is not material and therefore, the Company has not recorded any servicing assets or liabilities associated with the Factoring Agreement. See Note 3 for additional information. Inventory Inventory is recorded at the lower of cost or net realizable value, with cost determined on a first-in, first-out basis. Inventory costs include third-party contract manufacturing, third-party packaging services, and freight. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess and obsolete inventories to their estimated realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded within cost of sales. The determination of whether inventory costs will be realizable requires estimates by management. If actual market conditions are less favorable than projected by management, additional write-downs of inventory may be required which would be recorded as a cost of sales in the consolidated statements of operations and comprehensive loss. Inventory not expected to be sold within the Company’s normal operating cycle is classified as long-term inventory on the condensed consolidated balance sheet. Prior to regulatory approval of its product candidates, the Company expenses costs associated with the manufacturing of its product candidates to research and development expense unless the Company is reasonably certain such costs will have future commercial use and net realizable value. When the Company believes regulatory approval and subsequent commercialization of its product candidates is probable, and the Company also expects future economic benefit from the sales of the product candidates to be realized, the Company will then capitalize the costs of production as inventory. Inventory that can be used in either the production of clinical or commercial product is expensed as research and development expense when selected for use in a clinical manufacturing campaign. Prior to receiving FDA approval for EMPAVELI on May 14, 2021, the Company included in research and development expense the costs associated with the manufacture of EMPAVELI inventory to be sold upon commercialization. As a result, the manufacturing costs related to the EMPAVELI inventory build-up incurred before FDA approval were expensed in a prior period and are, therefore, excluded from the cost of goods sold and inventory. As of September 30, 2024 and December 31, 2023, the remaining pre-FDA approved inventory was $ 15.4 million and $ 19.4 million, respectively, which primarily consisted of raw materials. Shipping and handling costs for product shipments are recorded as incurred in cost of sales along with costs associated with manufacturing the product and any inventory write-downs. Recently Issued Accounting Standards In December 2023, the Financial Accounting Standards Board (“FASB”) issued an amendment to the accounting guidance on income taxes which requires entities to provide additional information in the rate reconciliation and additional disaggregated disclosures about income taxes paid. This guidance requires public entities to disclose in their rate reconciliation table additional categories of information about federal, state, and foreign income taxes and to provide more details about the reconciling items in some categories if the items meet a quantitative threshold. The guidance is effective for annual periods beginning after December 15, 2024. The Company is currently evaluating this guidance to determine the impact it may have on its consolidated financial statements and disclosures. In November 2023, the FASB issued an amendment to the accounting guidance on segment reporting. The amendments require disclosure of significant segment expenses and other segment items and requires entities to provide in interim periods all disclosures about a reportable segment's profit or loss and assets that are currently required annually. The amendment also requires disclosure of the title and position of the chief operating decision maker (“CODM”) and an explanation of how the CODM uses the reported measure(s) of segment profit or loss in assessing segment performance and deciding how to allocate resources. The guidance is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Retrospective application is required, and early adoption is permitted. The Company is currently evaluating the impact the guidance will have on its consolidated financial statements and disclosures.

Product Revenues, Accounts Rece

Product Revenues, Accounts Receivable, and Reserves for Product Sales	9 Months Ended
	Sep. 30, 2024
Product Revenues Accounts Receivable And Reserves For Product Sales [Abstract]
Product Revenues, Accounts Receivable, and Reserves for Product Sales	3. Product Revenues, Accounts Receivable, and Reserves for Product Sales The Company received FDA approval for the sale of EMPAVELI in the United States in May 2021 and approval for the sale of SYFOVRE in the United States in February 2023. The Company’s product revenues consist of sales of EMPAVELI and SYFOVRE to specialty pharmacies and specialty distributors. The table reflects product revenue by major source for the following periods (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Products: EMPAVELI $ 24,611 $ 23,901 $ 74,733 $ 66,643 SYFOVRE 151,960 75,281 444,049 160,983 Total Product revenue, net $ 176,571 $ 99,182 $ 518,782 $ 227,626 The Company’s accounts receivable balance of $ 279.0 million as of September 30, 2024 and $ 206.4 million as of December 31, 2023, consisted of EMPAVELI and SYFOVRE product sales receivable and licensing and other revenue receivables from our collaboration with Swedish Orphan Biovitrum AB (“Sobi”) . The Company does not have a reserve related to expected credit losses against its receivable balance and expects to collect its accounts receivable in the ordinary course of business. The Company’s product revenue allowance and reserves totaled $ 32.9 million and $ 16.6 million as of September 30, 2024 and December 31, 2023, respectively. These amounts are included in accrued expenses on the Company’s unaudited condensed consolidated balance sheets. Th e following table summarizes activity in each of the product revenue allowance and reserve categories for the three and nine months ended September 30, 2024 (in thousands): Chargebacks, Discounts, and Fees Government and Other Rebates Returns Total Ending balance at December 31, 2023 $ 5,674 $ 8,898 $ 2,053 $ 16,625 Provision related to sales in the current year 9,575 13,125 1,355 24,055 Adjustments related to prior period sales 146 ( 19 ) ( 96 ) 31 Credits and payments made ( 9,724 ) ( 9,906 ) ( 1,859 ) ( 21,489 ) Ending balance at March 31, 2024 $ 5,671 $ 12,098 $ 1,453 $ 19,222 Provision related to sales in the current year 10,025 17,777 1,039 28,841 Adjustments related to prior period sales ( 131 ) 354 ( 983 ) ( 760 ) Credits and payments made ( 9,635 ) ( 14,640 ) ( 326 ) ( 24,601 ) Ending balance at June 30, 2024 $ 5,930 $ 15,589 $ 1,183 $ 22,702 Provision related to sales in the current year 11,455 25,364 1,380 38,199 Adjustments related to prior period sales 2,332 420 — 2,752 Credits and payments made ( 12,078 ) ( 17,695 ) ( 979 ) ( 30,752 ) Ending balance at September 30, 2024 $ 7,639 $ 23,678 $ 1,584 $ 32,901 The following table summarizes activity in each of the product revenue allowance and reserve categories for the three and nine months ended September 30, 2023 (in thousands): Chargebacks, Discounts, and Fees Government and other rebates Returns Total Ending balance at December 31, 2022 $ 164 $ 1,936 $ 251 $ 2,351 Provision related to sales in the current year 1,466 2,566 651 4,683 Adjustments related to prior period sales — ( 2 ) ( 249 ) ( 251 ) Credits and payments made ( 184 ) ( 1,639 ) — ( 1,823 ) Ending balance at March 31, 2023 $ 1,446 $ 2,861 $ 653 $ 4,960 Provision related to sales in the current year 3,944 5,114 1,588 10,646 Adjustments related to prior period sales ( 84 ) 30 ( 416 ) ( 470 ) Credits and payments made ( 1,668 ) ( 2,946 ) ( 141 ) ( 4,755 ) Ending balance at June 30, 2023 $ 3,638 $ 5,059 $ 1,684 $ 10,381 Provision related to sales in the current year 4,698 7,169 1,384 13,251 Adjustments related to prior period sales 39 ( 964 ) ( 1,685 ) ( 2,610 ) Credits and payments made ( 4,960 ) ( 5,778 ) — ( 10,738 ) Ending balance at September 30, 2023 $ 3,415 $ 5,486 $ 1,383 $ 10,284 Significant customers - EMPAVELI and SYFOVRE are sold principally through arrangements with specialty pharmacies and specialty distributors, who are the Company’s customers. Gross product revenues and product sales receivable from the Company's customers who individually accounted for 10 % or more of total gross product revenues and/or 10 % or more of total product sales accounts receivable consisted of the following: Percent of Total Gross Product Revenues Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Customer A 12 % 24 % 13 % 29 % Customer C 17 % 16 % 18 % 14 % Customer D 61 % 56 % 59 % 52 % Percent of Product Sales Receivable As of September 30, 2024 2023 Customer A 3 % 7 % Customer C 24 % 19 % Customer D 61 % 68 % Factoring of accounts receivable and associated fees as of September 30, 2024 and December 31, 2023 were as follows (in thousands): September 30, December 31, 2024 2023 Accounts receivable sold $ 56,590 $ — Less: factoring fees ( 672 ) — Net cash proceeds $ 55,918 $ —

Inventory

Inventory	9 Months Ended
	Sep. 30, 2024
Inventory Disclosure [Abstract]
Inventory	4. Inventory The Company’s inventory consisted of the following as of September 30, 2024 and December 31, 2023 (in thousands): September 30, December 31, 2024 2023 Raw materials $ 46,639 $ 32,724 Semi-finished goods 113,708 82,924 Finished goods 6,791 30,714 Total inventory $ 167,138 $ 146,362 The Company's long-term inventory balance consists of raw materials that are not expected to be sold within the Company's normal operating cycle. Inventory amounts written down as a result of excess, obsolete, unmarketability or other reasons are charged to cost of sales. The Company's reserve for excess and obsolete inventory was $ 14.1 million and $ 9.3 million as of September 30, 2024 and December 31, 2023, respectively.

Prepaid and Other Current Asset

Prepaid and Other Current Assets	9 Months Ended
	Sep. 30, 2024
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid and Other Current Assets	5. Prepaid and Other Current Assets Prepaid and other current assets consisted of the following as of September 30, 2024 and December 31, 2023 (in thousands): September 30, December 31, 2024 2023 Down payments for inventory $ 8,251 $ 16,296 Prepaid research and development 6,582 13,931 Other prepaid expenses 8,976 8,593 Total prepaid assets $ 23,809 $ 38,820 September 30, December 31, 2024 2023 Royalties receivable $ 4,958 $ 3,054 Receivable from collaboration agreement (1) — 15,000 Deposits and other current assets 6,824 4,354 Total other current assets $ 11,782 $ 22,408 (1) In January 2024, the Company waived the remaining reimbursement payment of $ 15.0 million from Sobi in connection with the decision to discontinue the cold agglutinin disease (“CAD”) program.

Development Liability

Development Liability	9 Months Ended
	Sep. 30, 2024
Research and Development [Abstract]
Development Liability	6. Development Liability In 2019, the Company entered into a development funding agreement (as amended, the “SFJ agreement”) with SFJ Pharmaceuticals Group (“SFJ”), under which SFJ agreed to provide funding to the Company to support the development of pegcetacoplan for the treatment of patients with PNH. Under the SFJ agreement, SFJ paid the Company an aggregate of $ 140.0 million between June 2019 and January 2020. Under the SFJ agreement, the Company granted a security interest to SFJ in all of its assets, excluding intellectual property and license agreements to which it is a party. In connection with the grant of the security interest, the Company agreed to certain affirmative and negative covenants, including restrictions on its ability to pay dividends, incur additional debt or enter into licensing transactions with respect to its intellectual property, other than specified types of licenses. Following regulatory approval for the use of systemic pegcetacoplan as a treatment for PNH by the FDA in May 2021 and by the European Medicines Agency in December 2021, the Company became obligated to pay SFJ an aggregate of $ 460.0 million in payments over the period from the time of each regulatory approval until the sixth anniversary of each regulatory approval. The Company paid SFJ a total of $ 94.0 million through March 31, 2024. From December 15, 2021 to the final annual payment due in December 2027, the development liability was accreted from its initial carrying amount to the total payment amount using the effective interest rate method over the remaining life of the SFJ agreement. The difference between the carrying amount and the total payment amount is presented as a discount to the development liability. The accretion is recorded as interest expense in the unaudited condensed consolidated statement of operations. In May 2024, the Company paid its remaining obligations under the SFJ agreement in full with $ 326.5 million of proceeds from the Sixth Street Financing Agreement (as defined below) (see Note 8). Upon such payment, SFJ released its security interest in the Company’s assets at that time. The Company concluded that the development liability was extinguished as of the payoff date, and the difference of $ 1.9 million between the reacquisition price of $ 326.5 million and the net carrying value of the development liability of $ 324.6 million was recorded as a loss on the extinguishment of the development liability in the unaudited condensed consolidated statement of operations for the nine month period ended September 30, 2024. The following table summarizes the development liability (in thousands): September 30, 2024 December 31, 2023 Effective Development liability $ — $ 366,000 7.91 % Less: Unamortized discount to development liability — ( 50,353 ) Less: Current portion of development liability, net of discount — ( 75,830 ) Total long-term development liability $ — $ 239,817 For the three months ended September 30, 2024 the Company did no t record interest expense for the accretion of the development liability. For the nine months ended September 30, 2024 , interest expense of $ 8.9 million was recorded for the accretion of the development liability. For the three and nine months ended September 30, 2023 , interest expense of $ 6.4 million and $ 19.5 million, respectively, was recorded for the accretion of the development liability.

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2024
Payables and Accruals [Abstract]
Accrued Expenses	7. Accrued Expenses Accrued expenses consisted of the following as of September 30, 2024 and December 31, 2023 (in thousands): September 30, December 31, 2024 2023 Accrued research and development $ 24,509 $ 28,318 Accrued royalties 6,676 10,197 Accrued payroll liabilities 34,722 51,781 Accrued goods received not invoiced 19,623 5,902 Product revenue reserves 32,901 16,625 Other 21,404 14,983 Total $ 139,835 $ 127,806

Long-term Debt

Long-term Debt	9 Months Ended
	Sep. 30, 2024
Debt Disclosure [Abstract]
Long-term Debt	8. Long-term Debt Convertible Senior Notes On September 16, 2019, the Company completed a private offering of convertible notes (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. The Company used $ 28.4 million of the net proceeds to pay the cost of the capped call transactions in September 2019 described below. On May 12, 2020, the Company issued convertible notes (the “2020 Convertible Notes”) with an aggregate principal amount of $ 300.0 million. The net proceeds from the sale of the 2020 Convertible Notes were approximately $ 322.9 million after deducting the purchasers’ discounts and commission of $ 5.7 million and offering expenses of $ 0.3 million. The Company used $ 43.1 million of the net proceeds to pay the cost of the additional capped call transactions in May 2020 described below. The 2019 Convertible Notes and the 2020 Convertible Notes are referred to together as the Convertible Notes. The Convertible Notes are senior unsecured obligations of the Company and bear interest at a rate of 3.5 % per year payable semiannually in arrears on March 15 and September 15 of each year, beginning on March 15, 2020. The Convertible Notes will mature on September 15, 2026 , unless converted earlier, redeemed or repurchased in accordance with their terms. The Convertible Notes are convertible into shares of the Company’s common stock at an initial conversion rate of 25.3405 shares per $1,000 principal amount of Convertible Notes (equivalent to an initial conversion price of approximately $ 39.4625 per share of common stock). The conversion rate is subject to customary anti-dilution adjustments. In addition, following certain events that occur prior to the maturity date or if the Company delivers 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. On or after September 20, 2023 , the Company may redeem for cash all or a portion of the Convertible Notes, at its option, if the last reported sale price of the Company’s common stock has been at least 130 % of the conversion price then in effect for at least 20 trading days (whether or not consecutive), including the trading day immediately preceding the date on which the Company provides a notice of redemption, during any 30 consecutive trading day period ending on, and including, the trading day immediately preceding the date on which the Company provides notice of redemption. The redemption price will be equal to 100 % of the principal amount of the Convertible Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. If the Company calls any Convertible Notes for redemption, it will constitute a “make-whole fundamental change” with respect to such Convertible Notes, in which case the conversion rate applicable to the conversion of such Notes, if converted in connection with the redemption, will be increased in certain circumstances. The Company has not called for redemption or redeemed any of the Convertible Notes as of September 30, 2024. 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. In January 2021, July 2021 and July 2022, the Company entered into separate, privately negotiated exchange agreements to modify the conversion terms with certain holders of its 2019 Convertible Notes and 2020 Convertible Notes. Under the terms of these exchange agreements, in January 2021, July 2021 and July 2022, the holders exchanged approximately $ 126.1 million of 2019 Convertible Notes, $ 201.1 million of 2019 Convertible Notes and 2020 Convertible Notes, and $ 98.1 million of 2020 Convertible Notes, respectively, in aggregate principal amount held by them for an aggregate of 3,906,869 shares, 5,992,217 shares and 3,027,018 shares, respectively, of common stock issued by the Company. In accordance with FASB ASC Topic 470-20, “ Debt – Debt with Conversion and Other Options,” (“ASC 470-20”) the Company accounted for the exchange as an induced conversion based on the short period of time the conversion offer was open and the substantive conversion feature offer. The Company accounted for the conversion of the debt as an inducement by expensing the fair value of the shares that were issued in excess of the original terms of the Convertible Notes. The conditional conversion feature of the Convertible Notes was triggered as of December 31, 2023, and as a result the Convertible Notes were convertible at the option of the holders until March 31, 2024. No Convertible Notes were converted during this period. The conditional conversion feature of the Convertible Notes was triggered as of March 31, 2024, and as a result the Convertible Notes were convertible at the option of the holders until June 30, 2024. No Convertible Notes were converted during this period. The conditional conversion feature of the Convertible Notes was not triggered as of June 30, 2024, and as a result the Convertible Notes are not convertible during the quarter ending September 30, 2024. The conditional conversion feature of the Convertible Notes was not triggered as of September 30, 2024, and as a result the Convertible Notes are not convertible during the quarter ending December 31, 2024. As of September 30, 2024 , the Company held in treasury Convertible Notes in principal amount of $ 425.4 million which notes had not been cancelled. The outstanding balance of the Convertible Notes as of September 30, 2024 and December 31, 2023 consisted of the following (in thousands): September 30, December 31, 2024 2023 Liability Principal $ 93,897 $ 93,897 Less: debt discount and issuance costs, net ( 634 ) ( 864 ) Net carrying amount $ 93,263 $ 93,033 The following table sets forth total interest expense recognized related to the Convertible Notes during the three and nine months ended September 30, 2024 and 2023 (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Amortization of debt issuance costs $ 78 $ 75 $ 230 $ 222 Contractual interest expense 822 822 2,465 2,465 Total interest expense $ 900 $ 897 $ 2,695 $ 2,687 Capped Call Transactions On September 11, 2019 and May 6, 2020, concurrently with the pricings of the Convertible Notes, the Company entered into capped call transactions with two counterparties. The capped call transactions are expected generally to reduce the potential dilution to the Company’s common stock upon any conversion of Convertible Notes and/or offset any cash payments the Company is required to make in excess of the principal amount of converted Convertible Notes, as the case may be, in the event that the market price per share of the Company’s common stock, as measured under the terms of the capped call transactions, is greater than the strike price of the capped call transactions, which is initially $ 39.4625 (the conversion price of the Convertible Notes) and is subject to anti-dilution adjustments substantially similar to those applicable to the conversion rate of such Convertible Notes. If, however, the market price per share of the Company’s common stock, as measured under the terms of the capped call transactions, exceeds the cap price of the capped call transactions, which is initially $ 63.14 per share, there would nevertheless be dilution and/or there would not be an offset of such potential cash payments, in each case, to the extent that such market price exceeds the cap price of the capped call transactions. On February 27, 2024, the Company unwound a portion of the capped call transactions with the capped call counterparties, which resulted in cash proceeds to the Company of $ 98.8 million. The unwind transactions were settled at a volume-weighted average price per share of $ 64.11 on March 8, 2024. As of September 30, 2024, the Company holds remaining capped call transactions in a notional amount corresponding to $ 93.9 million principal amount of Convertible Notes. Financing Agreement and Credit Facility On May 13, 2024, the Company and certain of its subsidiaries entered into a financing agreement (the “Sixth Street Financing Agreement”) with the lenders party thereto (the “Lenders”), and Sixth Street Lending Partners (“Sixth Street”), as the administrative agent and collateral agent for the Lenders. The Sixth Street Financing Agreement provides for a senior secured term loan facility of up to $ 475.0 million (the “Credit Facility”), consisting of an initial draw of $ 375.0 million at closing and a potential additional $ 100.0 million draw at the Company’s option upon satisfaction of a $ 50.0 million minimum cash requirement and a requirement that the Company’s trailing three-month sales of SYFOVRE is at least $ 180.0 million prior to the $ 100.0 million draw. The Company can exercise the option for the $ 100.0 million draw through September 30, 2025, assuming such requirements are met. The Credit Facility matures on May 13, 2030 (the “Maturity Date”) and bears interest at (i) in the case of SOFR Loans, an annual rate equal to 3-month Term SOFR (subject to 1.00 % floor), plus 5.75 %, and (ii) in the case of Base Rate Loans, an annual rate equal to the base rate as defined in the agreement (subject to 2.00 % floor), plus 4.75 %. Certain additional commitment and undrawn amount fees are also payable in connection with the Credit Facility. The net proceeds from the initial draw of the Credit Facility were approximately $ 358.2 million, net of $ 16.8 million of issuance costs. The Company used $ 326.5 million of the proceeds from the initial draw of the Credit Facility to buy out its remaining obligations to SFJ. The buyout of the SFJ development liability eliminated $ 366.0 million in payments to SFJ between 2024 and 2027, including approximately $ 200.0 million payable through 2025 (See Note 6). The Credit Facility does not provide for scheduled amortization payments during the term. All principal will be due on the Maturity Date. The Company will have the right to prepay loans under the Credit Facility at any time. The Company is required to repay loans under the Credit Facility with proceeds from certain asset sales, condemnation events and extraordinary receipts, subject, in some cases, to reinvestment rights. Repayments are subject to a prepayment premium. Repayments may be made after the first year of the loan and are subject to a prepayment premium up to 3 % depending on timing. All obligations under the Sixth Street Financing Agreement are secured on a first-priority basis, subject to certain exceptions, by security interests in substantially all assets of the Company and certain subsidiaries of the Company, including its intellectual property, and are guaranteed by certain subsidiaries of the Company, including foreign subsidiaries, subject to certain exceptions. The Sixth Street Financing Agreement contains customary covenants, including, without limitation, a financial covenant to maintain liquidity of at least $ 50.0 million if the Company’s market capitalization is below $3.0 billion, and negative covenants that, subject to certain exceptions, restrict indebtedness, liens, investments (including acquisitions), fundamental changes, asset sales and licensing transactions, dividends, modifications to material agreements, payment of subordinated indebtedness, and other matters customarily restricted in such agreements. Among other permissions, the Company is permitted, on terms and conditions set forth on the Sixth Street Financing Agreement, to enter into a separate asset-based financing arrangement with a third party in an amount of up to $ 100.0 million, which amount is increased to $ 200.0 million upon certain sales or market capitalization thresholds, and to have outstanding convertible unsecured notes in an amount equal to the greater of $ 400.0 million and 10 % of the Company’s market capitalization, but not to exceed $ 600.0 million. The Company is subject to restrictions on sales and licensing transactions with respect to its core intellectual property, defined to include SYFOVRE, EMPAVELI, and other pegcetacoplan product assets, subject to certain exceptions, including certain transactions related to areas outside the United States and Europe. The outstanding balance of the Credit Facility as of September 30, 2024 and December 31, 2023 consisted of the following (in thousands): September 30, December 31, 2024 2023 Liability Principal $ 375,000 $ — Less: debt discount and issuance costs ( 16,018 ) — Net carrying amount $ 358,982 $ — The following table sets forth total interest expense recognized related to the Credit Facility during the three and nine months ended September 30, 2024 and 2023 (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Amortization of debt issuance costs $ 581 $ — $ 742 $ — Contractual interest expense 10,854 — 16,160 — Total interest expense $ 11,435 $ — $ 16,902 $ —

Leases

Leases	9 Months Ended
	Sep. 30, 2024
Leases [Abstract]
Leases	9. Leases The underlying assets of the Company’s leases primarily relate to office space leases, but also include some equipment leases. The Company determines if an arrangement qualifies as a lease at its inception. As of September 30, 2024 and December 31, 2023 , all leases were classified as operating leases. Additional information related to the operating lease assets and liabilities is as follows (in thousands): September 30, December 31, 2024 2023 Right-of-use assets $ 17,060 $ 16,745 Operating lease liabilities $ 18,203 $ 17,895 Weighted average remaining term in years 2.84 2.83 Weighted average discount rate used to measure 6.30 % 7.20 % For the three months ended September 30, 2024 and 2023, the total lease cost for operating lease expense was $ 1.7 million and $ 1.8 million, respectively. For the nine months ended September 30, 2024 and 2023, the total lease cost for operating lease expense was $ 5.6 million and $ 5.2 million, respectively. Supplemental cash flow information related to operating leases for the nine months ended September 30, 2024 and 2023 is as follows (in thousands): 2024 2023 Operating cash flows from operating leases $ 5,992 $ 6,186 The maturities of the Company’s operating lease liabilities as of September 30, 2024 are as follows (in thousands): 2024 $ 1,966 2025 7,421 2026 6,763 2027 2,064 2028 and thereafter 1,485 Total future minimum lease payments 19,699 Less imputed interest ( 1,496 ) Total operating lease liabilities $ 18,203

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	10 . 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, 2024 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Cash and cash equivalents: Money market funds $ 202,967 $ — $ — $ 202,967 Total Financial Assets $ 202,967 $ — $ — $ 202,967 December 31, 2023 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Cash and cash equivalents Money market funds $ 276,391 $ — $ — $ 276,391 Total Financial Assets $ 276,391 $ — $ — $ 276,391 The Company’s Convertible Notes and development liability are financial instruments that are reported in the financial statements at historical cost. The Convertible Notes are Level 1 within the fair value level hierarchy as of September 30, 2024 and December 31, 2023. The fair value of the Convertible Notes was $ 103.6 million as of September 30, 2024 and $ 140.8 million as of December 31, 2023. The Convertible Notes accrue a semi-annual coupon at an annual rate of 3.5 %, which was included in accrued expenses in the consolidated balance sheets as of September 30, 2024 and December 31, 2023. The fair value of the development liability was $ 306.9 million as of December 31, 2023. The development liability is Level 2 within the fair value hierarchy based on the discounting of fixed cash flows using an observed bond yield for borrowers with similar credit rating. Because the development liability was paid in full in May 2024, no amount is included as of September 30, 2024.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2024
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Ta xes For the three and nine months ended September 30, 2024 , the Company recorded $ 0.6 million and $ 0.9 million of income tax expense, respectively, primarily pertaining to state and foreign income taxes. For the three and nine months ended September 30, 2023, the Company recorded $ 0.2 million and $ 0.7 million of income tax expense, respectively, primarily pertaining to state and foreign income taxes. The income tax provision during interim periods is computed by applying an estimated annual effective tax rate to year-to-date pre-tax income, plus adjustments for significant unusual or infrequently occurring items, in accordance with FASB ASC Topic 740-270, Income Taxes – Interim Reporting . The income tax provision differs from the U.S. federal statutory rate of 21 % primarily due to the effect of valuation allowance against the Company’s net deferred tax assets, which reduces the Company’s net tax benefit. 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 net deferred tax assets as of September 30, 2024 and December 31, 2023. 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. The Company has no t recorded any amounts for unrecognized tax benefits as of September 30, 2024 and December 31, 2023 . Our policy is to review and update unrecognized tax positions as facts and circumstances change.

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended
	Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License and Collaboration Agreements	12. License and Collaboration Agreements Sobi License and Collaboration Agreement In October 2020, the Company and its subsidiaries, Apellis Switzerland GmbH and APL DEL Holdings, LLC, entered into a Collaboration and License Agreement (the “Sobi collaboration agreement”) with Sobi, concerning the development and commercialization of pegcetacoplan and specified other structurally and functionally similar compstatin analogues or derivatives for use systemically or for local non-ophthalmological administration (collectively referred to as the “Licensed Products”). Under the Sobi collaboration agreement, the Company granted Sobi an exclusive (subject to certain retained rights of the Company), sublicensable license of certain patent rights and know-how to develop and commercialize Licensed Products in all countries outside of the United States. The Company retains the right to commercialize Licensed Products in the United States, and, subject to specified limitations, to develop Licensed Products worldwide for commercialization in the United States. Under the Sobi collaboration agreement, the Company and Sobi agreed to collaborate to develop Licensed Products for certain indications, including PNH, C3G, IC-MPGN and HSCT-TMA (collectively the “Initial Indications”), and any other indications subsequently agreed upon by the parties, for commercialization by or on behalf of the Company in the United States and by or on behalf of Sobi outside of the United States. If the parties do not agree to jointly pursue any development activities for the Licensed Products (whether for an Initial Indication or otherwise), the party proposing to pursue such activities may conduct such activities at its sole expense (with the non-proposing party having the right to obtain rights to the data generated by such development activities by paying a specified percentage of that expense), subject to agreed-upon exceptions that limit each party’s unilateral development rights. The initial development plan sets forth the initial development activities to be conducted by each of the Company and Sobi, with the Company bearing all costs incurred in conducting the activities set forth in such initial development plan, as well as certain specified additional costs that are not included in the initial development plan that may be incurred by the parties in developing Licensed Products for PNH in the European Union and the United Kingdom. The Company and Sobi 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 Sobi collaboration agreement grants Sobi the right to perform or have performed drug product manufacturing of Licensed Products for development and for commercialization outside the United States and to manufacture or have manufactured drug substance under certain circumstances. Sobi paid the Company an upfront payment of $ 250.0 million in November 2020 and agreed to pay up to an aggregate of $ 915.0 million upon the achievement of specified one-time regulatory and commercial milestone events, of which the Company received $ 50.0 million in April 2022 for the achievement of a regulatory development milestone in Europe. Sobi also agreed to reimburse the Company for up to $ 80.0 million in development costs, of which the Company received a total of $ 65.0 million through January 2023 and waived the remaining payment of $ 15.0 million in January, 2024. 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 Sobi collaboration agreement, the Company remains responsible for its license fee obligations (including royalty obligations) to the Trustees of the University of Pennsylvania (“Penn”), as a licensor of the Company. Under the Sobi collaboration agreement, for the three and nine months ended September 30, 2024 , the Company recognized $ 5.0 million and $ 13.9 million, respectively, of royalty revenue. For the three and nine months ended September 30, 2023 , the Company recognized $ 2.7 million and $6 .8 million, respectively, of royalty revenue. For the three and nine months ended September 30, 2024 and 2023, the Company did no t recognize any contra-research and development expense in the unaudited condensed consolidated statement of operations related to the $ 80.0 million reimbursement commitment from Sobi. Since contract inception, the Company has recognized $ 65.0 million in contra-research and development expenses and waived the remaining $ 15.0 mill ion in connection with the decision to discontinue the CAD program. As of December 31, 2023, the Company recorded $ 15.0 million in current assets, which represented the receivable for contra-research and development expenses incurred but not yet reimbursed from Sobi. In January 2024, the Company waived the remaining reimbursement payment of $ 15.0 mill ion in connection with the decision to discontinue the CAD program. University of Pennsylvania License Agreement The Company is a party to a license agreement with 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, subject to a step-down upon patent expiry, with minimum quarterly royalty thresholds. In addition, the Company is obligated to pay a specified portion of income it receives from sublicensees. In April 2023, the Company paid $ 2.3 million for the achievement of a regulatory milestone as a result of the FDA approval of SYFOVRE in February 2023. In 2023, the Company incurred $ 5.0 million as a result of the achievement of sales milestones for SYFOVRE of which the Company paid $ 2.0 million in October 2023 and the remaining $ 3.0 million in January 2024. For the three and nine months ended September 30, 2024, the Company incurred royalty expense of $ 4.9 million and $ 14.4 million on sales of SYFOVRE. For the three and nine months ended September 30, 2023, the Company has incurred royalty expense of $2.4 million and $5.2 million on sales of SYFOVRE. In addition, the Company is also party to a license agreement with Penn for an exclusive, worldwide license to specified patent rights for the development and commercialization of products in fields of use, as defined therein. The Company is required to 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 a step-down upon patent expiry, with 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 a sublicense fee owed to Penn related to the Sobi collaboration agreement and another licensing transaction. In August 2021, the Company paid $ 1.0 million to Penn upon the achievement of a development milestone, net of a credit for the annual license maintenance payment. In June 2022, the Company paid an additional $ 5.0 million to Penn upon the achievement of a development milestone. In January 2023, the Company paid $ 1.0 million to Penn upon the achievement of a sales milestone for EMPAVELI in 2022. In January 2024, the Company paid $ 0.5 million for a sublicense fee owed to Penn related to Sobi obtaining regulatory approval in Japan. Additionally, in January 2024, the Company paid $ 1.5 million as a result of the achievement of a sales milestone for EMPAVELI and Aspaveli. For the three and nine months ended September 30, 2024, the Company incurred royalty expense of $ 1.8 million and $ 5.0 million on sales of EMPAVELI and Aspaveli. For the three and nine months ended September 30, 2023 , the Company has incurred royalty expense of $1.3 million and $3.4 million on sales of EMPAVELI and Aspaveli.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. Commitments and Contingencies The Company has certain non-cancelable purchase obligations related to the manufacturing of drug substance and drug product. The Company has agreed to purchase from Bachem Americas, Inc. a significant portion of its requirements for the pegcetacoplan drug substance. Under a commercial supply agreement with NOF Corporation ("NOF"), the Company has agreed to purchase activated polyethylene glycol derivative, or PEG, which is a component of pegcetacoplan. In September 2024, the Company terminated the minimum purchase obligation with NOF for 2025. Under these agreements, as of September 30, 2024, the Company is obligated to pay up to an aggregate of $ 56.1 million to these vendors. As a result of this termination, the Company incurred an expense of $ 6.4 million, which is included in Other Liabilities on the consolidated balance sheet. In addition, the Company has other non-cancelable purchase agreements as of September 30, 2024, under which it is obligat ed to pay up to an aggregate of $ 17.5 million to vendors. The Company is a party to a master lease agreement under which the Company leases vehicles with initial terms of 36 months from the date of delivery. If the Company were unable to take delivery of a previously ordered vehicle, the Company may incur nominal fees. Indemnifications —In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend indemnified parties for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third-party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has no t 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. On August 2, 2023, Judith M. Soderberg filed a putative class action in the United States District Court for the District of Delaware against the Company and certain current and former executive officers of the Company (the “Complaint”). The Complaint alleges, among other things, that the defendants violated Sections 10(b) and/or 20(a) of the Exchange Act and Rule 10b-5 promulgated thereunder by misrepresenting and/or omitting certain material facts related to the design of SYFOVRE’s clinical trials and the risks associated with SYFOVRE’s commercial adoption. The Complaint seeks, among other relief, compensatory damages and equitable relief in favor of the alleged class against all defendants, including interest, and reasonable costs and expenses incurred by plaintiffs, including attorneys’ and expert fees. On October 2, 2023, the defendants moved to transfer the action to the United States District Court for the District of Massachusetts. On October 23, 2023, the Court appointed Ray Peleckas and Michigan Laborers’ Pension Fund together as Co-Lead Plaintiffs and assigned the action the caption In Apellis Pharmaceuticals, Inc. Securities Litigation, Case 1:23-cv-00834-MN. The Co-Lead Plaintiffs filed an amended complaint on February 8, 2024 (the “Amended Complaint”). The Amended Complaint is brought on behalf of a class of all persons and entities who purchased or otherwise acquired Apellis common stock between January 28, 2021 and July 28, 2023, inclusive, names the Company and Cedric Francois, our chief executive officer, as defendants, and makes similar allegations, asserts the same claims and seeks the same relief as the Complaint. On May 17, 2024, the United States District Court for the District of Delaware approved the motion to transfer to the United States District Court for the District of Massachusetts. The defendants moved to dismiss the Complaint on June 12, 2024, and the Court has scheduled oral argument on this motion for November 14, 2024. The Company’s businesses may also be subject at any time to other commercial disputes, product liability claims, personal injury claims, third-party subpoenas or various other lawsuits arising in the ordinary course of business, including intellectual property infringement, employment or investor matters, and the Company expects that this will continue to be the case in the future. For example, in August 2024, an individual filed a civil action against the Company in the United States District Court in the Northern District of Texas, alleging personal injury claims in connection with the use of SYFOVRE. We moved to dismiss this civil action in September 2024. The Court has not yet ruled on this motion to dismiss, as of the date of issuance of these unaudited condensed consolidated financial statements. The outcome of the matters described above cannot be predicted with certainty and therefore any loss is neither probable nor reasonably estimable. However, the Company intends to vigorously defend against these matters.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2024
Earnings Per Share [Abstract]
Net Loss per Share	14. Net Loss per Share Basic and diluted net loss per share is calculated based upon the weighted average number of shares of common stock outstanding during the period. Shares of the Company’s common stock underlying pre-funded warrants are included in the weighted average number of shares of common stock used to calculate basic and diluted net loss per share attributable to common stockholders as they are exercisable at any time for nominal cash. 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 would have been anti-dilutive. Convertible notes and potential common shares 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): As of September 30, 2024 2023 Convertible notes 2,379 2,379 Common stock options 8,063 9,738 Restricted stock units 4,017 4,449 Total 14,459 16,566

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2024
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. 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, 2023 has been derived from audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments (consisting only of normal recurring adjustments) that are necessary for a fair presentation of the Company’s financial information. The results of operations for the three and nine months ended September 30, 2024 are not necessarily indicative of the results to be expected for the year ending December 31, 2024 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, 2023 included in the Company’s Annual Report on Form 10-K filed with the SEC on February 27, 2024, as amended by Amendment No. 1 thereto filed with the SEC on February 29, 2024 (the “2023 Form 10-K”).
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: development liability, accrued expenses, prepaid expenses, convertible debt, reserves for variable consideration, reserves for excess or obsolete inventories, and income taxes.
Accounts Receivable	Accounts Receivable The Company’s accounts receivable primarily arise from product sales. They are generally stated at the invoiced amount and do not bear interest. The accounts receivable from product sales represents receivables due from the Company’s SPs or SDs. The Company has had no historical write offs of its accounts receivable as of September 30, 2024 and December 31, 2023, and its payment terms are generally 30-65 days for EMPAVELI and 60-150 days for SYFOVRE. The Company monitors the financial performance and creditworthiness of its customers and provides reserves against trade receivables for expected credit losses that may result from a customer’s inability to pay. Amounts determined to be uncollectible are written-off against the established reserve. As of September 30, 2024 and December 31, 2023, 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.
Factoring Agreement	The Company has an agreement (the “Factoring Agreement”) to sell certain trade accounts receivable to a third-party financial institution at a discount to the invoiced amount. Under the Factoring Agreement, the maximum amount of outstanding accounts receivables sold at any time is $100.0 million. The Company accounts for the transfer of trade accounts receivable under the Factoring Agreement as a sale in accordance with ASC 860, Transfers and Servicing , because effective control and risk associated with the transferred accounts receivable is passed to the third-party. Accordingly, the Company derecognizes the sold trade accounts receivable from the consolidated balance sheets. Cash proceeds related to the accounts receivable sold are included in cash from operating activities in the consolidated statements of cash flows. Any discounts or fees incurred in connection with the sales are recorded within “Selling, general and administrative expenses" in the consolidated statements of operations and comprehensive loss. Pursuant to the Factoring Agreement, the Company performs certain collection and administrative functions for the receivable sold. The fair value of these administrative services is not material and therefore, the Company has not recorded any servicing assets or liabilities associated with the Factoring Agreement. See Note 3 for additional information.
Inventory	Inventory Inventory is recorded at the lower of cost or net realizable value, with cost determined on a first-in, first-out basis. Inventory costs include third-party contract manufacturing, third-party packaging services, and freight. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess and obsolete inventories to their estimated realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded within cost of sales. The determination of whether inventory costs will be realizable requires estimates by management. If actual market conditions are less favorable than projected by management, additional write-downs of inventory may be required which would be recorded as a cost of sales in the consolidated statements of operations and comprehensive loss. Inventory not expected to be sold within the Company’s normal operating cycle is classified as long-term inventory on the condensed consolidated balance sheet. Prior to regulatory approval of its product candidates, the Company expenses costs associated with the manufacturing of its product candidates to research and development expense unless the Company is reasonably certain such costs will have future commercial use and net realizable value. When the Company believes regulatory approval and subsequent commercialization of its product candidates is probable, and the Company also expects future economic benefit from the sales of the product candidates to be realized, the Company will then capitalize the costs of production as inventory. Inventory that can be used in either the production of clinical or commercial product is expensed as research and development expense when selected for use in a clinical manufacturing campaign. Prior to receiving FDA approval for EMPAVELI on May 14, 2021, the Company included in research and development expense the costs associated with the manufacture of EMPAVELI inventory to be sold upon commercialization. As a result, the manufacturing costs related to the EMPAVELI inventory build-up incurred before FDA approval were expensed in a prior period and are, therefore, excluded from the cost of goods sold and inventory. As of September 30, 2024 and December 31, 2023, the remaining pre-FDA approved inventory was $ 15.4 million and $ 19.4 million, respectively, which primarily consisted of raw materials. Shipping and handling costs for product shipments are recorded as incurred in cost of sales along with costs associated with manufacturing the product and any inventory write-downs.
Recently Issued Accounting Standards	Recently Issued Accounting Standards In December 2023, the Financial Accounting Standards Board (“FASB”) issued an amendment to the accounting guidance on income taxes which requires entities to provide additional information in the rate reconciliation and additional disaggregated disclosures about income taxes paid. This guidance requires public entities to disclose in their rate reconciliation table additional categories of information about federal, state, and foreign income taxes and to provide more details about the reconciling items in some categories if the items meet a quantitative threshold. The guidance is effective for annual periods beginning after December 15, 2024. The Company is currently evaluating this guidance to determine the impact it may have on its consolidated financial statements and disclosures. In November 2023, the FASB issued an amendment to the accounting guidance on segment reporting. The amendments require disclosure of significant segment expenses and other segment items and requires entities to provide in interim periods all disclosures about a reportable segment's profit or loss and assets that are currently required annually. The amendment also requires disclosure of the title and position of the chief operating decision maker (“CODM”) and an explanation of how the CODM uses the reported measure(s) of segment profit or loss in assessing segment performance and deciding how to allocate resources. The guidance is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Retrospective application is required, and early adoption is permitted. The Company is currently evaluating the impact the guidance will have on its consolidated financial statements and disclosures.

Product Revenues, Accounts Re_2

Product Revenues, Accounts Receivable, and Reserves for Product Sales (Tables)	9 Months Ended
	Sep. 30, 2024
Product Revenues Accounts Receivable And Reserves For Product Sales [Abstract]
Schedule of Disaggregation of Product Revenue by Major Source	The table reflects product revenue by major source for the following periods (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Products: EMPAVELI $ 24,611 $ 23,901 $ 74,733 $ 66,643 SYFOVRE 151,960 75,281 444,049 160,983 Total Product revenue, net $ 176,571 $ 99,182 $ 518,782 $ 227,626
Summary of Product Revenue Allowance and Reserve Categories	Th e following table summarizes activity in each of the product revenue allowance and reserve categories for the three and nine months ended September 30, 2024 (in thousands): Chargebacks, Discounts, and Fees Government and Other Rebates Returns Total Ending balance at December 31, 2023 $ 5,674 $ 8,898 $ 2,053 $ 16,625 Provision related to sales in the current year 9,575 13,125 1,355 24,055 Adjustments related to prior period sales 146 ( 19 ) ( 96 ) 31 Credits and payments made ( 9,724 ) ( 9,906 ) ( 1,859 ) ( 21,489 ) Ending balance at March 31, 2024 $ 5,671 $ 12,098 $ 1,453 $ 19,222 Provision related to sales in the current year 10,025 17,777 1,039 28,841 Adjustments related to prior period sales ( 131 ) 354 ( 983 ) ( 760 ) Credits and payments made ( 9,635 ) ( 14,640 ) ( 326 ) ( 24,601 ) Ending balance at June 30, 2024 $ 5,930 $ 15,589 $ 1,183 $ 22,702 Provision related to sales in the current year 11,455 25,364 1,380 38,199 Adjustments related to prior period sales 2,332 420 — 2,752 Credits and payments made ( 12,078 ) ( 17,695 ) ( 979 ) ( 30,752 ) Ending balance at September 30, 2024 $ 7,639 $ 23,678 $ 1,584 $ 32,901 The following table summarizes activity in each of the product revenue allowance and reserve categories for the three and nine months ended September 30, 2023 (in thousands): Chargebacks, Discounts, and Fees Government and other rebates Returns Total Ending balance at December 31, 2022 $ 164 $ 1,936 $ 251 $ 2,351 Provision related to sales in the current year 1,466 2,566 651 4,683 Adjustments related to prior period sales — ( 2 ) ( 249 ) ( 251 ) Credits and payments made ( 184 ) ( 1,639 ) — ( 1,823 ) Ending balance at March 31, 2023 $ 1,446 $ 2,861 $ 653 $ 4,960 Provision related to sales in the current year 3,944 5,114 1,588 10,646 Adjustments related to prior period sales ( 84 ) 30 ( 416 ) ( 470 ) Credits and payments made ( 1,668 ) ( 2,946 ) ( 141 ) ( 4,755 ) Ending balance at June 30, 2023 $ 3,638 $ 5,059 $ 1,684 $ 10,381 Provision related to sales in the current year 4,698 7,169 1,384 13,251 Adjustments related to prior period sales 39 ( 964 ) ( 1,685 ) ( 2,610 ) Credits and payments made ( 4,960 ) ( 5,778 ) — ( 10,738 ) Ending balance at September 30, 2023 $ 3,415 $ 5,486 $ 1,383 $ 10,284
Schedule of Customer Accounted for 10% of More of Gross Product Revenues and Accounts Receivable	Significant customers - EMPAVELI and SYFOVRE are sold principally through arrangements with specialty pharmacies and specialty distributors, who are the Company’s customers. Gross product revenues and product sales receivable from the Company's customers who individually accounted for 10 % or more of total gross product revenues and/or 10 % or more of total product sales accounts receivable consisted of the following: Percent of Total Gross Product Revenues Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Customer A 12 % 24 % 13 % 29 % Customer C 17 % 16 % 18 % 14 % Customer D 61 % 56 % 59 % 52 % Percent of Product Sales Receivable As of September 30, 2024 2023 Customer A 3 % 7 % Customer C 24 % 19 % Customer D 61 % 68 %
Schedule of Factoring of Accounts Receivable and Associated Fees	Factoring of accounts receivable and associated fees as of September 30, 2024 and December 31, 2023 were as follows (in thousands): September 30, December 31, 2024 2023 Accounts receivable sold $ 56,590 $ — Less: factoring fees ( 672 ) — Net cash proceeds $ 55,918 $ —

Inventory (Tables)

Inventory (Tables)	9 Months Ended
	Sep. 30, 2024
Inventory Disclosure [Abstract]
Schedule of Inventory	The Company’s inventory consisted of the following as of September 30, 2024 and December 31, 2023 (in thousands): September 30, December 31, 2024 2023 Raw materials $ 46,639 $ 32,724 Semi-finished goods 113,708 82,924 Finished goods 6,791 30,714 Total inventory $ 167,138 $ 146,362

Prepaid and Other Current Ass_2

Prepaid and Other Current Assets (Tables)	9 Months Ended
	Sep. 30, 2024
Prepaid Expense and Other Assets, Current [Abstract]
Summary of Prepaid and Other Current Assets	Prepaid and other current assets consisted of the following as of September 30, 2024 and December 31, 2023 (in thousands): September 30, December 31, 2024 2023 Down payments for inventory $ 8,251 $ 16,296 Prepaid research and development 6,582 13,931 Other prepaid expenses 8,976 8,593 Total prepaid assets $ 23,809 $ 38,820 September 30, December 31, 2024 2023 Royalties receivable $ 4,958 $ 3,054 Receivable from collaboration agreement (1) — 15,000 Deposits and other current assets 6,824 4,354 Total other current assets $ 11,782 $ 22,408 (1) In January 2024, the Company waived the remaining reimbursement payment of $ 15.0 million from Sobi in connection with the decision to discontinue the cold agglutinin disease (“CAD”) program.

Development Liability (Tables)

Development Liability (Tables)	9 Months Ended
	Sep. 30, 2024
Research and Development [Abstract]
Summary of Development Liability	The following table summarizes the development liability (in thousands): September 30, 2024 December 31, 2023 Effective Development liability $ — $ 366,000 7.91 % Less: Unamortized discount to development liability — ( 50,353 ) Less: Current portion of development liability, net of discount — ( 75,830 ) Total long-term development liability $ — $ 239,817

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2024
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following as of September 30, 2024 and December 31, 2023 (in thousands): September 30, December 31, 2024 2023 Accrued research and development $ 24,509 $ 28,318 Accrued royalties 6,676 10,197 Accrued payroll liabilities 34,722 51,781 Accrued goods received not invoiced 19,623 5,902 Product revenue reserves 32,901 16,625 Other 21,404 14,983 Total $ 139,835 $ 127,806

Long-term Debt (Tables)

Long-term Debt (Tables)	9 Months Ended
	Sep. 30, 2024
Debt Disclosure [Abstract]
Schedule of Outstanding Balance of Convertible Notes	The outstanding balance of the Convertible Notes as of September 30, 2024 and December 31, 2023 consisted of the following (in thousands): September 30, December 31, 2024 2023 Liability Principal $ 93,897 $ 93,897 Less: debt discount and issuance costs, net ( 634 ) ( 864 ) Net carrying amount $ 93,263 $ 93,033
Schedule of Interest Expense Recognized Related to Convertible Notes	The following table sets forth total interest expense recognized related to the Convertible Notes during the three and nine months ended September 30, 2024 and 2023 (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Amortization of debt issuance costs $ 78 $ 75 $ 230 $ 222 Contractual interest expense 822 822 2,465 2,465 Total interest expense $ 900 $ 897 $ 2,695 $ 2,687
Summary of Credit Facility	The outstanding balance of the Credit Facility as of September 30, 2024 and December 31, 2023 consisted of the following (in thousands): September 30, December 31, 2024 2023 Liability Principal $ 375,000 $ — Less: debt discount and issuance costs ( 16,018 ) — Net carrying amount $ 358,982 $ —
Summary of Interest Expense Recognized Related to Credit Facility	The following table sets forth total interest expense recognized related to the Credit Facility during the three and nine months ended September 30, 2024 and 2023 (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Amortization of debt issuance costs $ 581 $ — $ 742 $ — Contractual interest expense 10,854 — 16,160 — Total interest expense $ 11,435 $ — $ 16,902 $ —

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2024
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, 2024 2023 Right-of-use assets $ 17,060 $ 16,745 Operating lease liabilities $ 18,203 $ 17,895 Weighted average remaining term in years 2.84 2.83 Weighted average discount rate used to measure 6.30 % 7.20 %
Supplemental Cash Flow Information Related to Operating Leases	Supplemental cash flow information related to operating leases for the nine months ended September 30, 2024 and 2023 is as follows (in thousands): 2024 2023 Operating cash flows from operating leases $ 5,992 $ 6,186
Maturities of Operating Lease Liabilities	The maturities of the Company’s operating lease liabilities as of September 30, 2024 are as follows (in thousands): 2024 $ 1,966 2025 7,421 2026 6,763 2027 2,064 2028 and thereafter 1,485 Total future minimum lease payments 19,699 Less imputed interest ( 1,496 ) Total operating lease liabilities $ 18,203

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2024
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, 2024 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Cash and cash equivalents: Money market funds $ 202,967 $ — $ — $ 202,967 Total Financial Assets $ 202,967 $ — $ — $ 202,967 December 31, 2023 Balance Sheet Classification Type of Instrument Level 1 Level 2 Level 3 Total Financial Assets: Cash and cash equivalents Money market funds $ 276,391 $ — $ — $ 276,391 Total Financial Assets $ 276,391 $ — $ — $ 276,391

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2024
Earnings Per Share [Abstract]
Summary of Potential Common Shares that were Excluded from Calculation of Diluted Net Loss Per Share	Convertible notes and potential common shares 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): As of September 30, 2024 2023 Convertible notes 2,379 2,379 Common stock options 8,063 9,738 Restricted stock units 4,017 4,449 Total 14,459 16,566

Nature of Organization and Op_2

Nature of Organization and Operations - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 396,864	$ 351,185	$ 452,414
Accumulated deficit	$ (2,999,013)	$ (2,837,488)

Basis of Presentation and Sum_3

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Inventory	$ 121,058	$ 146,362
Regulatory Approval Granted US Food and Drug Administration [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Inventory	$ 15,400	$ 19,400

Product Revenues, Accounts Re_3

Product Revenues, Accounts Receivable, and Reserves for Product Sales - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Accounts receivable	$ 279,011		$ 279,011		$ 206,442
Accrued Expenses [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Product revenue allowance and reserves	$ 32,900		$ 32,900		$ 16,600
Customer Concentration Risk [Member] | Gross Product Revenues [Member] | Product [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Concentration risk percentage	10%	10%	10%	10%
Customer Concentration Risk [Member] | Product Sales Accounts Receivable [Member] | Product [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Concentration risk percentage	10%	10%	10%	10%

Product Revenues, Accounts Re_4

Product Revenues, Accounts Receivable, and Reserves for Product Sales - Schedule of Disaggregation of Product Revenue by Major Source (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Total Product revenue, net	$ 196,830	$ 110,399	$ 568,839	$ 250,214
EMPAVELI [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Total Product revenue, net	24,611	23,901	74,733	66,643
SYFOVRE [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Total Product revenue, net	151,960	75,281	444,049	160,983
Product Revenue, Net [Member]
Product Revenues Accounts Receivable And Reserves For Product Sales [Line Items]
Total Product revenue, net	$ 176,571	$ 99,182	$ 518,782	$ 227,626

Product Revenues, Accounts Re_5

Product Revenues, Accounts Receivable, and Reserves for Product Sales - Summary of Product Revenue Allowance and Reserve Categories (Detail) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023
Chargebacks, Discounts, and Fees [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 5,930	$ 5,671	$ 5,674	$ 3,638	$ 1,446	$ 164
Provision related to sales in the current year	11,455	10,025	9,575	4,698	3,944	1,466
Adjustments related to prior period sales	2,332	(131)	146	39	(84)
Credits and payments made	(12,078)	(9,635)	(9,724)	(4,960)	(1,668)	(184)
Ending balance	7,639	5,930	5,671	3,415	3,638	1,446
Government and Other Rebates [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	15,589	12,098	8,898	5,059	2,861	1,936
Provision related to sales in the current year	25,364	17,777	13,125	7,169	5,114	2,566
Adjustments related to prior period sales	420	354	(19)	(964)	30	(2)
Credits and payments made	(17,695)	(14,640)	(9,906)	(5,778)	(2,946)	(1,639)
Ending balance	23,678	15,589	12,098	5,486	5,059	2,861
Returns [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	1,183	1,453	2,053	1,684	653	251
Provision related to sales in the current year	1,380	1,039	1,355	1,384	1,588	651
Adjustments related to prior period sales		(983)	(96)	(1,685)	(416)	(249)
Credits and payments made	(979)	(326)	(1,859)		(141)
Ending balance	1,584	1,183	1,453	1,383	1,684	653
Product Revenue Allowance and Reserves [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	22,702	19,222	16,625	10,381	4,960	2,351
Provision related to sales in the current year	38,199	28,841	24,055	13,251	10,646	4,683
Adjustments related to prior period sales	2,752	(760)	31	(2,610)	(470)	(251)
Credits and payments made	(30,752)	(24,601)	(21,489)	(10,738)	(4,755)	(1,823)
Ending balance	$ 32,901	$ 22,702	$ 19,222	$ 10,284	$ 10,381	$ 4,960

Product Revenues, Accounts Re_6

Product Revenues, Accounts Receivable, and Reserves for Product Sales - Schedule of Customer Accounted for 10% of More of Gross Product Revenues and Accounts Receivable (Detail) - Customer Concentration Risk [Member]	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Gross Product Revenues [Member] | Customer A [Member]
Revenue, Major Customer [Line Items]
Concentration risk	12%	24%	13%	29%
Gross Product Revenues [Member] | Customer C [Member]
Revenue, Major Customer [Line Items]
Concentration risk	17%	16%	18%	14%
Gross Product Revenues [Member] | Customer D [Member]
Revenue, Major Customer [Line Items]
Concentration risk	61%	56%	59%	52%
Product Sales Accounts Receivable [Member] | Customer A [Member]
Revenue, Major Customer [Line Items]
Concentration risk			3%	7%
Product Sales Accounts Receivable [Member] | Customer C [Member]
Revenue, Major Customer [Line Items]
Concentration risk			24%	19%
Product Sales Accounts Receivable [Member] | Customer D [Member]
Revenue, Major Customer [Line Items]
Concentration risk			61%	68%

Product Revenues, Accounts Re_7

Product Revenues, Accounts Receivable, and Reserves for Product Sales - Schedule of Factoring of Accounts Receivable and Associated Fees (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2024 USD ($)
Product Revenues Accounts Receivable And Reserves For Product Sales [Abstract]
Accounts receivable sold	$ 56,590
Less: factoring fees	(672)
Net cash proceeds	$ 55,918

Inventory - Schedule of Invento

Inventory - Schedule of Inventory (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Inventory Disclosure [Abstract]
Raw materials	$ 46,639	$ 32,724
Semi-finished goods	113,708	82,924
Finished goods	6,791	30,714
Inventory, Total	$ 167,138	$ 146,362

Inventory - Additional Informat

Inventory - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Inventory Disclosure [Abstract]
Reserve for excess and obsolete inventory	$ 14.1	$ 9.3

Prepaid and Other Current Ass_3

Prepaid and Other Current Assets - Summary of Prepaid and Other Current Assets (Detail) - USD ($) $ in Thousands		Sep. 30, 2024	Dec. 31, 2023
Prepaid Expense and Other Assets, Current [Abstract]
Down payments for inventory		$ 8,251	$ 16,296
Prepaid research and development		6,582	13,931
Other prepaid expenses		8,976	8,593
Total prepaid assets		23,809	38,820
Royalties receivable		4,958	3,054
Receivable from collaboration agreement	[1]		15,000
Deposits and other current assets		6,824	4,354
Total other current assets		$ 11,782	$ 22,408
[1] In January 2024, the Company waived the remaining reimbursement payment of $ 15.0 million from Sobi in connection with the decision to discontinue the cold agglutinin disease (“CAD”) program.

Prepaid and Other Current Ass_4

Prepaid and Other Current Assets - Summary of Prepaid and Other Current Assets (Parenthetical) (Detail) $ in Millions	1 Months Ended
	Jan. 31, 2024 USD ($)
Prepaid Expense and Other Assets, Current [Abstract]
Development cost reimbursement received	$ 15

Development Liability - Additio

Development Liability - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended			8 Months Ended	9 Months Ended
	May 13, 2024	May 31, 2024	Sep. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jan. 31, 2020	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2021
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from credit facility							$ 365,454,000
Loss on extinguishment of development liability							1,949,000
Interest expense			$ 12,532,000		$ 7,310,000		28,857,000	$ 22,179,000
Sixth Financing Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from credit facility	$ 326,500,000	$ 326,500,000
SFJ Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from SFJ agreement						$ 140,000,000
Payment made under agreement				$ 94,000,000
Loss on extinguishment of development liability							1,900,000
Interest expense			0		$ 6,400,000		8,900,000	$ 19,500,000
Development liability reacquisition price			326,500,000				326,500,000
Development liability carrying value			$ 324,600,000				$ 324,600,000
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									$ 460,000,000

Development Liability - Summary

Development Liability - Summary of Development Liability (Detail) - SFJ Agreement [Member] - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development liability		$ 366,000
Less: Unamortized discount to development liability		(50,353)
Less: Current portion of development liability, net of discount		(75,830)
Total long term development liability		$ 239,817
Effective Interest Rate	7.91%	7.91%

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Accrued research and development	$ 24,509	$ 28,318
Accrued royalties	6,676	10,197
Accrued payroll liabilities	34,722	51,781
Accrued goods received not invoiced	19,623	5,902
Product revenue reserves	32,901	16,625
Other	21,404	14,983
Total accrued expenses	$ 139,835	$ 127,806

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Detail)

1 Months Ended

3 Months Ended

9 Months Ended

May 13, 2024 USD ($)

Feb. 27, 2024 USD ($)

May 12, 2020 USD ($)

Sep. 16, 2019 USD ($)

Jul. 31, 2022 USD ($) shares

Jul. 31, 2021 USD ($) shares

Jan. 31, 2021 USD ($) shares

Sep. 30, 2024 USD ($) $ / shares

Sep. 30, 2023 USD ($)

Sep. 30, 2024 USD ($) Days $ / shares

Sep. 30, 2023 USD ($)

Mar. 08, 2024 $ / shares

Dec. 31, 2023 USD ($)

Nov. 09, 2019 CounterParty $ / shares

Debt Instrument [Line Items]

Conversion ratio

25,340.5000

Proceeds from credit facility

$ 365,454,000

SFJ Agreement [Member]

Debt Instrument [Line Items]

Payment for buyout of development liability elimination

$ 366,000,000

Payment for buyout of development liability which is due in 2025

$ 200,000

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

Credit facility maturity date

Sep. 15, 2026

Threshold trading days | Days

20

Threshold consecutive trading days | Days

30

Threshold percentage of stock price trigger

130%

Redemption period, start date

Sep. 20, 2023

Redemption price, percentage

100%

Debt interest expense

$ 900,000

$ 897,000

$ 2,695,000

$ 2,687,000

Long-term debt outstanding amount

$ 93,263,000

$ 93,263,000

$ 93,033,000

Convertible Senior Notes Due 2026 [Member] | Prior to March 15, 2026 Convertible [Member]

Debt Instrument [Line Items]

Threshold trading days | Days

20

Threshold consecutive trading days | Days

30

Threshold percentage of stock price trigger

130%

Trading price per principal amount

$ 1,000,000

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%

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). 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 delivers 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.

Conversion price | $ / shares

$ 39.4625

$ 39.4625

2019 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [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

2019 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [Member] | Exchange Agreements [Member]

Debt Instrument [Line Items]

Aggregate principal amount converted

$ 126,100,000

2019 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [Member] | Common Stock [Member] | Exchange Agreements [Member]

Debt Instrument [Line Items]

Aggregate principal amount converted into shares | shares

3,906,869

2020 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [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

2020 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [Member] | Exchange Agreements [Member]

Debt Instrument [Line Items]

Aggregate principal amount converted

$ 98,100,000

Convertible notes held in treasury

$ 425,400,000

$ 425,400,000

2020 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [Member] | Common Stock [Member] | Exchange Agreements [Member]

Debt Instrument [Line Items]

Aggregate principal amount converted into shares | shares

3,027,018

5,992,217

2019 and 2020 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [Member] | Exchange Agreements [Member]

Debt Instrument [Line Items]

Aggregate principal amount converted

$ 201,100,000

Capped Call Transactions [Member]

Debt Instrument [Line Items]

Volume-weighted average price per share | $ / shares

$ 64.11

Call transactions remaining is a notional amount

$ 93,900,000

$ 93,900,000

Proceeds from issuance of common stock

$ 98,800,000

Number of counterparties | CounterParty

2

Initial conversion price | $ / shares

$ 39.4625

Initial cap price | $ / shares

$ 63.14

Private Offering [Member] | 2019 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [Member]

Debt Instrument [Line Items]

Principal amount

$ 220,000,000

Private Offering [Member] | 2020 Convertible Notes [Member] | Convertible Senior Notes Due 2026 [Member]

Debt Instrument [Line Items]

Principal amount

$ 300,000,000

Long-term Debt - Financing Agre

Long-term Debt - Financing Agreement and Credit Facility (Additional Information) (Details) - USD ($)		1 Months Ended	9 Months Ended
	May 13, 2024	May 31, 2024	Sep. 30, 2024
Debt Instrument [Line Items]
Proceeds from credit facility			$ 365,454,000
S F J Agreement [Member]
Debt Instrument [Line Items]
Payment for buyout of development liability elimination	$ 366,000,000
Payment for buyout of development liability which is due in 2025	200,000
SYFOVRE [Member]
Debt Instrument [Line Items]
Minimum required sales to draw additional loan under credit facility	180,000,000
Sixth Street Financing Agreement [Member]
Debt Instrument [Line Items]
Proceeds from initial draw amount under credit facility	358,200,000
Proceeds from net of isuance cost	16,800,000
Proceeds from credit facility	326,500,000	$ 326,500,000
Senior Secured Credit Facility [Member] | Asset-Based Financing Arrangement [Member]
Debt Instrument [Line Items]
Available additional draw amount upon satisfaction of cash requirements	100,000,000
Available Additional Draw Amount Upon Satisfaction of Cash Requirements	100,000,000
Senior Secured Credit Facility [Member] | Sixth Street Financing Agreement [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	475,000,000
Available initial draw amount under credit facility	375,000,000
Available additional draw amount upon satisfaction of cash requirements	100,000,000
Minimum cash requirements to draw additional loan under credit facility	50,000,000
Minimum required sales to draw additional loan under credit facility	100,000
Excercise option draw amount under credit facility	$ 100,000,000
Credit facility maturity date	May 13, 2030
Debt instrument, covenant description			The Sixth Street Financing Agreement contains customary covenants, including, without limitation, a financial covenant to maintain liquidity of at least $50.0 million if the Company’s market capitalization is below $3.0 billion, and negative covenants that, subject to certain exceptions, restrict indebtedness, liens, investments (including acquisitions), fundamental changes, asset sales and licensing transactions, dividends, modifications to material agreements, payment of subordinated indebtedness, and other matters customarily restricted in such agreements. Among other permissions, the Company is permitted, on terms and conditions set forth on the Sixth Street Financing Agreement, to enter into a separate asset-based financing arrangement with a third party in an amount of up to $100.0 million, which amount is increased to $200.0 million upon certain sales or market capitalization thresholds, and to have outstanding convertible unsecured notes in an amount equal to the greater of $400.0 million and 10% of the Company’s market capitalization, but not to exceed $600.0 million. The Company is subject to restrictions on sales and licensing transactions with respect to its core intellectual property, defined to include SYFOVRE, EMPAVELI, and other pegcetacoplan product assets, subject to certain exceptions, including certain transactions related to areas outside the United States and Europe.
Minimum required financial covenant if capitalization below three billion	$ 50,000
Available Additional Draw Amount Upon Satisfaction of Cash Requirements	$ 100,000,000
Market capitalization threshold percentage for credit facility	10%
Senior Secured Credit Facility [Member] | Sixth Street Financing Agreement [Member] | Asset-Based Financing Arrangement [Member]
Debt Instrument [Line Items]
Revised Additional Available Draw Amount Upon Satisfaction of Sales or Market capitalization	$ 200,000,000
Minimum required convertible unsecured notes for additional loan amount	400,000,000
Market Capitalization Threshold for Credit Facility	$ 600,000,000
Senior Secured Credit Facility [Member] | Sixth Street Financing Agreement [Member] | SOFR [Member]
Debt Instrument [Line Items]
Variable interest rate percentage on base rate	1%
Senior Secured Credit Facility [Member] | Sixth Street Financing Agreement [Member] | Base Rate [Member]
Debt Instrument [Line Items]
Variable interest rate percentage on base rate	2%
Credit Facility [Member] | Sixth Street Financing Agreement [Member]
Debt Instrument [Line Items]
Debt instrument effective interest rate	5.75%
Credit Facility [Member] | Sixth Street Financing Agreement [Member] | Base Rate [Member]
Debt Instrument [Line Items]
Debt instrument effective interest rate	4.75%
Credit Facility [Member] | Maximum [Member] | Sixth Street Financing Agreement [Member]
Debt Instrument [Line Items]
Percentage of prepayment premium	3%

Long-term Debt - Schedule of Ou

Long-term Debt - Schedule of Outstanding Balance of Convertible Notes (Detail) - Convertible Senior Notes Due 2026 [Member] - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Principal	$ 93,897	$ 93,897
Less: debt discount and issuance costs	(634)	(864)
Net carrying amount	$ 93,263	$ 93,033

Long-term Debt - Schedule of In

Long-term Debt - Schedule of Interest Expense Recognized Related to Convertible Notes (Detail) - Convertible Senior Notes Due 2026 [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Debt Instrument [Line Items]
Amortization of debt issuance costs	$ 78	$ 75	$ 230	$ 222
Contractual interest expense	822	822	2,465	2,465
Total interest expense	$ 900	$ 897	$ 2,695	$ 2,687

Long-term Debt - Summary of Cre

Long-term Debt - Summary of Credit Facility (Detail) - Credit Facility [Member] $ in Thousands	Sep. 30, 2024 USD ($)
Debt Instrument [Line Items]
Principal	$ 375,000
Less: debt discount and issuance costs	(16,018)
Net carrying amount	$ 358,982

Long Term Debt - Summary of Int

Long Term Debt - Summary of Interest Expense Recognized Related to Credit Facility (Detail) - Credit Facility [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2024
Debt Instrument [Line Items]
Amortization of debt issuance costs	$ 581	$ 742
Contractual interest expense	10,854	16,160
Total interest expense	$ 11,435	$ 16,902

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Lessee Lease Description [Line Items]
Operating lease expense	$ 1.7	$ 1.8	$ 5.6	$ 5.2

Leases - Schedule of Additional

Leases - Schedule of Additional Information Related to Operating Lease Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Leases [Abstract]
Right-of-use assets	$ 17,060	$ 16,745
Operating lease liabilities	$ 18,203	$ 17,895
Weighted average remaining term in years	2 years 10 months 2 days	2 years 9 months 29 days
Weighted average discount rate used to measure outstanding lease liabilities	6.30%	7.20%

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information Related to Operating Leases (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Leases [Abstract]
Operating cash flows from operating leases	$ 5,992	$ 6,186

Leases - Maturities of Operatin

Leases - Maturities of Operating Lease Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Leases [Abstract]
2024	$ 1,966
2025	7,421
2026	6,763
2027	2,064
2028 and thereafter	1,485
Total future minimum lease payments	19,699
Less imputed interest	(1,496)
Total operating lease liabilities	$ 18,203	$ 17,895

Other Comprehensive Income and

Other Comprehensive Income and Accumulated Other Comprehensive Income - Summary of Changes in Accumulated Other Comprehensive Income/(Loss), by Component (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ 264,327	$ 266,676	$ 194,521	$ 232,271	$ 345,403	$ 412,123	$ 169,872
Ending balance	237,121	264,327	266,676	194,521	232,271	345,403	412,123
Total Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(3,362)	(3,525)	(3,542)	(1,065)	(796)	(775)	(875)
Ending balance	$ (3,140)	$ (3,362)	$ (3,525)	$ (3,542)	$ (1,065)	$ (796)	$ (775)

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, 2024	Dec. 31, 2023
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 202,967	$ 276,391
Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	202,967	276,391
Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	202,967	276,391
Level 1 [Member] | Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Financial Assets	$ 202,967	$ 276,391

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	Sep. 30, 2024	Dec. 31, 2023
Level 1 [Member] | Convertible Senior Notes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Convertible notes	$ 103,600,000	$ 140,800,000
Convertible notes, interest rate	3.50%	3.50%
Level 2 [Member] | Development Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value	$ 0	$ 306,900,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income tax expense	$ 592,000	$ 233,000	$ 876,000	$ 709,000
U.S. federal statutory rate			21%
Minimum percentage of tax position likelihood of being realized upon examination by taxing authorities			50%
Unrecognized tax benefits	$ 0		$ 0		$ 0

License and Collaboration Agr_2

License and Collaboration Agreements - Additional Information (Detail)			1 Months Ended							3 Months Ended		9 Months Ended		12 Months Ended	47 Months Ended
	Nov. 30, 2020 USD ($)	Oct. 27, 2020 USD ($)	Jan. 31, 2024 USD ($)	Oct. 31, 2023 USD ($)	Apr. 30, 2023 USD ($)	Jan. 31, 2023 USD ($)	Jun. 30, 2022 USD ($)	Apr. 30, 2022 USD ($)	Aug. 31, 2021 USD ($)	Sep. 30, 2024 USD ($) License	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) License	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Sep. 30, 2024 USD ($) License	Jan. 31, 2021 USD ($)	Oct. 31, 2020 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development cost reimbursement received			$ 15,000,000
Revenue										$ 196,830,000	$ 110,399,000	$ 568,839,000	$ 250,214,000
Number of licensed products | License										2		2			2
EMPAVELI [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue										$ 24,611,000	23,901,000	$ 74,733,000	66,643,000
SYFOVRE [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue										151,960,000	75,281,000	444,049,000	160,983,000
Regulatory milestone payments			3,000,000	$ 2,000,000	$ 2,300,000
Royalty expense										4,900,000		14,400,000
Regulatory milestone incurred														$ 5,000,000
EMPAVELI and Aspaveli [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments based on annual sales milestones			1,500,000
Royalty expense										1,800,000		5,000,000
Swedish Orphan Biovitrum AB (Publ) [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty Revenue										5,000,000	2,700,000	$ 13,900,000	800,000
Collaboration and License Agreement [Member] | Swedish Orphan Biovitrum AB (Publ) [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment	$ 250,000,000
Milestone payment received for achievement of regulatory development milestone								$ 50,000,000
Development cost reimbursement received						$ 65,000,000
Waived Payment			15,000,000												$ 15,000,000
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 expense										0	$ 0	$ 0	$ 0		65,000,000
Contract research and development current														$ 15,000,000
Remaining reimbursement payment			15,000,000
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 development and commercial milestone events																	$ 915,000,000
Development cost reimbursement												80,000,000
University of Pennsylvania [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Annual maintenance fees												100,000
Development milestone achievement							$ 5,000,000		$ 1,000,000
University of Pennsylvania [Member] | EMPAVELI and Aspaveli [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments based on annual sales milestones						$ 1,000,000
University of Pennsylvania [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate milestones payments										3,200,000		3,200,000			3,200,000
Milestone payments based on annual sales milestones												5,000,000
2010 License Agreement [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate milestones payments										$ 1,700,000		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			$ 500,000													$ 25,000,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Commitments And Contingencies [Line Items]
Other liabilities	$ 9,829,000	$ 2,312,000
Incurred any cost to defend lawsuits or settle claims	$ 0
Vehicles [Member]
Commitments And Contingencies [Line Items]
Operating lease, term of contract	36 months
Bachem Americas, Inc [Member]
Commitments And Contingencies [Line Items]
Non-cancellable purchase commitments	$ 56,100,000
Other liabilities	6,400,000
Other non-cancellable purchase commitments	$ 17,500,000

Net Loss per Share - Summary of

Net Loss per Share - Summary of Potential Common Shares that were Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	14,459	16,566
Convertible Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	2,379	2,379
Common Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	8,063	9,738
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	4,017	4,449