Sage Therapeutics (SAGE) 10-Q 2 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 26, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Trading Symbol	SAGE
Entity Registrant Name	Sage Therapeutics, Inc.
Entity Central Index Key	0001597553
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		58,908,485
Entity Shell Company	false
Entity File Number	001-36544
Entity Tax Identification Number	27-4486580
Entity Address, Address Line One	215 First Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	299-8380
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 422,165	$ 1,661,082
Marketable securities	1,421,004	438,467
Prepaid expenses and other current assets	34,343	22,821
Collaboration receivable - related party	24,185
Total current assets	1,901,697	2,122,370
Property and equipment, net	2,907	6,755
Restricted cash	1,269	1,716
Right-of-use operating asset	17,432	25,064
Other long-term assets	3,875	3,341
Total assets	1,927,180	2,159,246
Current liabilities:
Accounts payable	4,733	3,691
Accrued expenses	66,795	54,851
Operating lease liability, current portion	7,414	8,662
Total current liabilities	78,942	67,204
Operating lease liability, net of current portion	12,481	19,438
Other liabilities	103	270
Total liabilities	91,526	86,912
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at September 30, 2021 and December 31, 2020; no shares issued or outstanding at September 30, 2021 and December 31, 2020
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at September 30, 2021 and December 31, 2020; 58,835,406 and 58,311,444 shares issued at September 30, 2021 and December 31, 2020; 58,832,373 and 58,308,411 shares outstanding at September 30, 2021 and December 31, 2020	6	6
Treasury stock, at cost, 3,033 shares at September 30, 2021 and December 31, 2020	(400)	(400)
Additional paid-in capital	3,207,028	3,109,807
Accumulated deficit	(1,370,674)	(1,037,494)
Accumulated other comprehensive gain (loss)	(306)	415
Total stockholders’ equity	1,835,654	2,072,334
Total liabilities and stockholders’ equity	$ 1,927,180	$ 2,159,246

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	58,835,406	58,311,444
Common stock, shares outstanding	58,832,373	58,308,411
Treasury stock, shares	3,033	3,033

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Total revenue	$ 1,440	$ 1,639	$ 4,666	$ 5,014
Operating costs and expenses:
Cost of goods sold	131	149	466	429
Research and development	83,497	74,078	207,723	211,008
Selling, general and administrative	48,706	35,099	131,899	143,454
Restructuring		(529)		27,873
Total operating costs and expenses	132,334	108,797	340,088	382,764
Loss from operations	(130,894)	(107,158)	(335,422)	(377,750)
Interest income, net	692	1,347	2,132	8,763
Other income, net	31	76	110	165
Net loss	$ (130,171)	$ (105,735)	$ (333,180)	$ (368,822)
Net loss per share—basic and diluted	$ (2.21)	$ (2.03)	$ (5.69)	$ (7.10)
Weighted average number of common shares outstanding—basic and diluted	58,819,548	51,981,468	58,593,743	51,938,923
Comprehensive loss:
Net loss	$ (130,171)	$ (105,735)	$ (333,180)	$ (368,822)
Other comprehensive items:
Unrealized loss on marketable securities	(21)	(763)	(721)	(349)
Total other comprehensive loss	(21)	(763)	(721)	(349)
Total comprehensive loss	$ (130,192)	$ (106,498)	$ (333,901)	$ (369,171)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities
Net loss	$ (333,180)	$ (368,822)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	83,981	75,250
Premium on marketable securities	(19,792)	(1,066)
Amortization of premium on marketable securities	8,722	628
Depreciation	3,849	1,981
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(11,522)	(3,647)
Collaboration receivable - related party	(24,185)
Other long-term assets	(534)	366
Right-of-use operating asset	3,898	4,914
Operating lease liabilities, current	152	(6)
Operating lease liabilities, non-current	(4,427)	(5,194)
Accounts payable	1,042	(10,913)
Accrued expenses and other liabilities	11,315	(40,182)
Net cash used in operating activities	(280,681)	(346,691)
Cash flows from investing activities
Proceeds from sales and maturities of marketable securities	699,212	766,339
Purchases of marketable securities	(1,671,399)	(368,829)
Purchases of property and equipment		(345)
Net cash provided by (used in) investing activities	(972,187)	397,165
Cash flows from financing activities
Proceeds from stock option exercises and employee stock purchase plan issuances	14,300	7,091
Net cash provided by financing activities	13,504	7,091
Payment of employee tax obligations related to vesting of restricted stock units	(796)
Net increase (decrease) in cash, cash equivalents and restricted cash	(1,239,364)	57,565
Cash, cash equivalents and restricted cash at beginning of period	1,662,798	129,072
Cash, cash equivalents and restricted cash at end of period	423,434	186,637
Supplemental disclosure of non-cash operating and investing activities
Lease asset de-recognized upon lease cancellation	$ 3,733	$ 2,310

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balances at Dec. 31, 2019	$ 944,655	$ 5	$ (400)	$ 2,587,322	$ 1,295	$ (1,643,567)
Balances, Shares at Dec. 31, 2019		51,877,194	3,033
Issuance of common stock from exercises of stock options, Amount	367			367
Issuance of common stock from exercises of stock options, Shares		7,196
Issuance of common stock under the employee stock purchase plan	2,793			2,793
Issuance of common stock under the employee stock purchase plan, Shares		33,429
Stock-based compensation expense	30,218			30,218
Unrealized gain (loss) on available-for-sale securities	(2,087)				(2,087)
Net loss	(126,740)					(126,740)
Balances at Mar. 31, 2020	849,206	$ 5	$ (400)	2,620,700	(792)	(1,770,307)
Balance, Shares at Mar. 31, 2020		51,917,819	3,033
Balances at Dec. 31, 2019	944,655	$ 5	$ (400)	2,587,322	1,295	(1,643,567)
Balances, Shares at Dec. 31, 2019		51,877,194	3,033
Net loss	(368,822)
Balances at Sep. 30, 2020	657,581	$ 5	$ (400)	2,669,419	946	(2,012,389)
Balance, Shares at Sep. 30, 2020		52,022,829	3,033
Balances at Mar. 31, 2020	849,206	$ 5	$ (400)	2,620,700	(792)	(1,770,307)
Balances, Shares at Mar. 31, 2020		51,917,819	3,033
Issuance of common stock from exercises of stock options, Amount	387			387
Issuance of common stock from exercises of stock options, Shares		17,160
Stock-based compensation expense	24,168			24,168
Unrealized gain (loss) on available-for-sale securities	2,501				2,501
Net loss	(136,347)					(136,347)
Balances at Jun. 30, 2020	739,915	$ 5	$ (400)	2,645,255	1,709	(1,906,654)
Balance, Shares at Jun. 30, 2020		51,934,979	3,033
Issuance of common stock from exercises of stock options, Amount	2,157			2,157
Issuance of common stock from exercises of stock options, Shares		48,560
Issuance of common stock under the employee stock purchase plan	2,144			2,144
Issuance of common stock under the employee stock purchase plan, Shares		39,290
Stock-based compensation expense	19,863			19,863
Unrealized gain (loss) on available-for-sale securities	(763)				(763)
Net loss	(105,735)					(105,735)
Balances at Sep. 30, 2020	657,581	$ 5	$ (400)	2,669,419	946	(2,012,389)
Balance, Shares at Sep. 30, 2020		52,022,829	3,033
Balances at Dec. 31, 2020	2,072,334	$ 6	$ (400)	3,109,807	415	(1,037,494)
Balances, Shares at Dec. 31, 2020		58,308,411	3,033
Issuance of common stock from exercises of stock options, Amount	4,687			4,687
Issuance of common stock from exercises of stock options, Shares		80,338
Issuance of common stock under the employee stock purchase plan	936			936
Issuance of common stock under the employee stock purchase plan, Shares		18,072
Stock-based compensation expense	21,734			21,734
Unrealized gain (loss) on available-for-sale securities	(651)				(651)
Net loss	(95,764)					(95,764)
Balances at Mar. 31, 2021	2,003,276	$ 6	$ (400)	3,137,164	(236)	(1,133,258)
Balance, Shares at Mar. 31, 2021		58,406,821	3,033
Balances at Dec. 31, 2020	2,072,334	$ 6	$ (400)	3,109,807	415	(1,037,494)
Balances, Shares at Dec. 31, 2020		58,308,411	3,033
Net loss	(333,180)
Balances at Sep. 30, 2021	1,835,654	$ 6	$ (400)	3,207,028	(306)	(1,370,674)
Balance, Shares at Sep. 30, 2021		58,832,373	3,033
Balances at Mar. 31, 2021	2,003,276	$ 6	$ (400)	3,137,164	(236)	(1,133,258)
Balances, Shares at Mar. 31, 2021		58,406,821	3,033
Issuance of common stock from exercises of stock options, Amount	6,861			6,861
Issuance of common stock from exercises of stock options, Shares		159,070
Stock-based compensation expense	27,465			27,465
Unrealized gain (loss) on available-for-sale securities	(49)				(49)
Vesting of restricted stock units, net of employee tax obligations	(796)			(796)
Vesting of restricted stock units, net of employee tax obligations, Shares		204,473
Net loss	(107,245)					(107,245)
Balances at Jun. 30, 2021	1,929,512	$ 6	$ (400)	3,170,694	(285)	(1,240,503)
Balance, Shares at Jun. 30, 2021		58,770,364	3,033
Issuance of common stock from exercises of stock options, Amount	430			430
Issuance of common stock from exercises of stock options, Shares		33,322
Issuance of common stock under the employee stock purchase plan	1,825			1,825
Issuance of common stock under the employee stock purchase plan, Shares		28,687
Stock-based compensation expense	34,079			34,079
Unrealized gain (loss) on available-for-sale securities	(21)				(21)
Net loss	(130,171)					(130,171)
Balances at Sep. 30, 2021	$ 1,835,654	$ 6	$ (400)	$ 3,207,028	$ (306)	$ (1,370,674)
Balance, Shares at Sep. 30, 2021		58,832,373	3,033

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Sage Therapeutics, Inc. (“Sage” or the “Company”) is a biopharmaceutical company committed to developing and commercializing novel medicines with the potential to transform the lives of people with debilitating disorders of the brain. The Company’s first product, ZULRESSO® (brexanolone) CIV injection, is approved in the U.S. as a treatment for postpartum depression (“PPD”) in adults. The Company launched ZULRESSO commercially in the U.S. in June 2019. The Company has a portfolio of other product candidates with a current focus on modulating two critical central nervous system (“CNS”) receptor systems, GABA and NMDA. The GABA receptor family, which is recognized as the major inhibitory neurotransmitter in the CNS, mediates downstream neurologic and bodily function via activation of GABA A The Company was incorporated under the laws of the State of Delaware on April 16, 2010, and commenced operations on January 19, 2011 as Sterogen Biopharma, Inc. On September 13, 2011, the Company changed its name to Sage Therapeutics, Inc. The Company is subject to risks and uncertainties common to companies in the biotechnology and pharmaceutical industries, including, but not limited to, the risks associated with developing product candidates at each stage of non-clinical and clinical development; the challenges associated with gaining regulatory approval of such product candidates; the risks associated with the marketing and sale of pharmaceutical products; the potential for development by third parties of new technological innovations that may compete with the Company’s products and product candidates; the dependence on key personnel; the challenges of protecting proprietary technology; the need to comply with government regulations; the high costs of drug development; the uncertainty of being able to secure additional capital when needed to fund operations; and the potential impact of the COVID-19 pandemic on its development activities, operations and financial condition. Under Accounting Standards Update (“ASU”) No. 2014-15, Presentation of Financial Statements—Going Concern except for net income of $606.1 million for the year ended December 31, 2020, reflecting revenue recognized under a collaboration and license agreement with Biogen MA Inc. (“BIMA”) and Biogen International GmbH (collectively with BIMA, “Biogen”) (the “Biogen Collaboration Agreement”) Until such time, if ever, as the Company can generate substantial product revenue and achieve profitability, the Company expects to finance its cash needs through a combination of equity offerings, debt financings, collaborations, strategic alliances, licensing arrangements and other sources of funding. If the Company is unable to raise additional funds through equity or debt financings or other sources of funding when needed, the Company may be required to delay, limit, reduce or terminate product development or future commercialization efforts or grant rights to develop and market products or product candidates that the Company would otherwise prefer to develop and market itself. The Company expects that, based on its current operating plans, the Company’s existing cash, cash equivalents and marketable securities will be sufficient to fund its currently planned operations for at least the next 12 months from the filing date of these unaudited interim condensed consolidated financial statements (“condensed consolidated financial statements”). COVID-19 The ongoing COVID-19 pandemic has caused and may continue to cause major disruptions to businesses and economies worldwide. The rapid spread of COVID-19 in the U.S. resulted in a significant reduction in patient demand for ZULRESSO and in the number of sites available to administer ZULRESSO. This has had a negative impact on the Company’s revenue from sales of ZULRESSO. While the Company has not experienced any other material disruptions to date as a result of the COVID-19 pandemic, any prolonged material disruptions to the work of the Company’s employees, suppliers, contract manufacturers, or vendors could negatively impact the Company’s activities, availability of supplies, or operating results. we have seen slower recruitment in certain of our clinical trials, due, we believe, to the COVID-19 pandemic, especially with respect to older patients and, in our SKYLARK Study, in patients with PPD, ny material disruption to the Company’s development activities may cause delays, increase the Company’s costs and impact the Company’s operating results. In addition, the COVID-19 pandemic initially caused major volatility in capital markets and a significant global economic downturn, and the Company’s ability to access the capital markets in the future could be negatively impacted if current efforts to control the COVID-19 pandemic are not successful.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies The following is a summary of significant accounting policies followed in the preparation of these condensed consolidated financial statements. Basis of Presentation The condensed consolidated financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2020, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. The condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements. In the opinion of the Company’s management, the accompanying condensed consolidated financial statements contain all adjustments, consisting of only normal recurring adjustments, necessary for a fair statement of its financial position as of September 30, 2021, its results of operations and comprehensive loss for the three and nine months ended September 30, 2021 and 2020, its cash flows for the nine months ended September 30, 2021 and 2020, and its statements of changes in stockholders’ equity for the three and nine months ended September 30, 2021 and 2020. The consolidated balance sheet at December 31, 2020 was derived from audited financial statements, but does not include all disclosures required by GAAP. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of the results for the year ending December 31, 2021, or for any future period. Principles of Consolidation The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries as disclosed in Note 2, Summary of Significant Accounting Policies Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The full extent to which the COVID-19 pandemic may directly or indirectly impact the Company’s business, results of operations and financial condition, including sales, expenses, reserves and allowances, manufacturing, clinical trials, research and development costs and employee-related amounts, will depend on future developments that are highly uncertain, including: the scope and duration of the pandemic; the effectiveness of vaccination campaigns, vaccine mandates, and other efforts to control the pandemic; the duration of the vaccines’ efficacy against COVID-19 and its variants; the duration and severity of any restrictive measures taken to curb the spread of COVID-19; and the impact of the pandemic on the Company’s customers and vendors. The Company has made estimates of the impact of the COVID-19 pandemic within its condensed consolidated financial statements. Due to the evolving nature of the COVID-19 pandemic, and the emergence of highly contagious variants, there may be changes to those estimates in future periods, and a Risks and Uncertainties The product candidates developed by the Company require approvals from the U.S. Food and Drug Administration (“FDA”) or foreign regulatory agencies prior to commercial sales. There can be no assurance that the current and future product candidates of the Company will receive the necessary approvals. If the Company Research and Development Costs and Accruals Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries and benefits, overhead costs, depreciation, contract services and other related costs. Research and development costs are expensed to operations as the related obligation is incurred. The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the U.S. These agreements are generally cancelable, and related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research and development costs. When billing terms under these contracts do not coincide with the timing of when the work is performed, the Company is required to make estimates of outstanding obligations to those third parties as of the end of the reporting period Revenue Recognition The Company generates revenue from the sale of ZULRESSO, which was approved by the FDA in March 2019 and the Company subsequently began selling in June 2019, and from collaboration and supply agreements with the Company’s collaborators. To date, revenue from collaboration agreements has come from initial, upfront payments allocated to licenses of intellectual property delivered to the Company’s collaborators and from the supply of material for clinical trials under a supply agreement Under Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: ( i ) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price, including variable consideration, if any; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, they are considered performance obligations. The exercise of a material right may be accounted for as a contract modification or as a continuation of the contract for accounting purposes. For contracts determined to be within the scope of Topic 606, the Company assesses whether the goods or services promised within each contract are distinct to identify those that are performance obligations. This assessment involves subjective determinations and requires management to make judgments about the individual promised goods or services and whether such are separable from the other aspects of the contractual relationship. Promised goods and services are considered distinct provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. The Company allocates the transaction price (the amount of consideration it expects to be entitled to from a customer in exchange for the promised goods or services) to each performance obligation and recognizes the associated revenue when (or as) each performance obligation is satisfied. The Company’s estimate of the transaction price for each contract includes all variable consideration to which the Company expects to be entitled. Collaboration and License Revenue In assessing whether a promised good or service is distinct in the evaluation of a collaboration or license arrangement subject to Topic 606, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner, and the availability of the associated expertise in the general marketplace. The Company also considers the intended benefit of the contract in assessing whether a promised good or service is separately identifiable from other promises in the contract. If a promised good or service is not distinct, the Company is required to combine that good or service with other promised goods or services until it identifies a bundle of goods or services that is distinct. The transaction price is then determined and allocated to the identified performance obligations in proportion to their standalone selling prices (“SSP”) on a relative SSP basis. SSP is determined at contract inception and is not updated to reflect changes between contract inception and when the performance obligations are satisfied. Determining the SSP for performance obligations requires significant judgment. In developing the SSP for a performance obligation, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. In certain circumstances, the Company may apply the residual method to determine the SSP of a good or service if the standalone selling price is considered highly variable or uncertain. The Company validates the SSP for performance obligations by evaluating whether changes in the key assumptions used to determine the SSP will have a significant effect on the allocation of arrangement consideration between multiple performance obligations. If the consideration promised in a contract includes a variable amount, the Company estimates the amount of consideration to which it will be entitled in exchange for transferring the promised goods or services to a customer. The Company determines the amount of variable consideration by using the expected value method or the most likely amount method. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment. If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company assessed its arrangements with Shionogi and Biogen and concluded that a significant financing component does not exist for either arrangement. For arrangements with licenses of intellectual property that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes royalty revenue and sales-based milestones at the later of (i) when the related sales occur, or (ii) when the performance obligation to which the royalty has been allocated has been satisfied. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied at a point in time or over time, and if over time this is based on the use of an output or input method. Revenue from the Company’s collaboration agreement with Shionogi has come from initial, upfront consideration upon execution of the agreement and for the supply of drug product for Shionogi’s clinical trials. Revenue from the Company’s collaboration agreement with Biogen has come from initial, upfront consideration related to the execution of the Biogen Collaboration Agreement. For additional information, refer to Note 6, Collaboration Agreements Product Revenue, Net The Company recognizes product revenues, net of variable consideration related to certain allowances and accruals that are determined using the expected value method, in its condensed consolidated financial statements at the point in time when control transfers to the customer, which is typically when the product has been delivered to the customer’s location. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. The Company’s only performance obligation identified for ZULRESSO is to deliver the product to the location specified by the customer’s order. The Company records shipping and handling costs associated with delivery of product to its customers within selling, general and administrative expenses on its condensed consolidated statements of operations and comprehensive loss. The Company expenses incremental costs of obtaining a contract as incurred if the expected amortization period of the asset would be less than one year. If the Company were to incur incremental costs with an amortization period greater than a year, such costs would be capitalized as contract assets, as they are expected to be recovered, and would be expensed by amortizing on a systematic basis that is consistent with the transfer to the customer of the goods or services to which the asset relates. The Company did not have any contract assets (unbilled receivables) at September 30, 2021, as customer invoicing generally occurs before or at the time of revenue recognition. The Company did not have any contract liabilities at September 30, 2021, as the Company did not receive any payments in advance of satisfying its performance obligations to its customers. Amounts billed or invoiced that are considered trade accounts receivable are included in prepaid expenses and other current assets on the condensed consolidated balance sheets. As of September 30, 2021 and December 31, 2020, the Company had not provided any allowance for bad debts against the trade accounts receivable, and the amount of trade accounts receivable was not significant. The Company records reserves, based on contractual terms, for the following components of variable consideration related to product sold during the reporting period, as well as its estimate of product that remains in the distribution channel inventory of its customers at the end of the reporting period. On a quarterly basis, the Company updates its estimates, if necessary, and records any material adjustments in the period they are identified. Chargebacks : The Company estimates chargebacks from its customers who directly purchase the product from the Company for discounts resulting from contractual commitments to sell products to eligible healthcare settings at prices lower than the list prices charged to its customers. Customers charge the Company for the difference between what they pay to the Company for the product and the selling price to the eligible healthcare settings. Reserves for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel inventories at the end of each reporting period that the Company expects will be sold to eligible healthcare settings, and chargebacks that customers have claimed, but for which the Company has not yet issued a credit. Government Rebates : The Company is subject to discount obligations under government programs, including Medicaid. The Company records reserves for rebates in the same period the related product revenue is recognized, resulting in a reduction of ZULRESSO product revenues and a current liability that is included in accrued expenses on its condensed consolidated balance sheets. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimates of future claims that will be made for product that has been recognized as revenue, but which remains in the distribution channel at the end of each reporting period. Trade Discounts and Allowances : The Company generally provides customary invoice discounts on ZULRESSO sales to its customers for prompt payment and the Company pays fees for sales order management, data, and distribution services. The Company estimates its customers will earn these discounts and fees and deducts these discounts and fees in full from gross ZULRESSO revenues and accounts receivable at the time the Company recognizes the related revenues. Financial Assistance : The Company provides voluntary financial assistance programs to patients with commercial insurance that have coverage and reside in states that allow financial assistance. The Company estimates the financial assistance amounts for ZULRESSO and records any such amounts within accrued expenses on its condensed consolidated balance sheets. The calculation of the accrual for financial assistance is based on an estimate of claims and the cost per claim that the Company expects to receive using demographics for patients who have registered and been approved for assistance. Any adjustments are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability, which is included as a component of accrued expenses on the condensed consolidated balance sheets. Product Returns : Consistent with industry practice, the Company offers product return rights to direct customers for damaged, defective or expiring product, provided it is within a specified period around the product expiration date as set forth in the Company’s return goods policy. The Company estimates the amount of its product sales that may be returned by its customers and records this estimate as a reduction of revenue in the period the related product revenue is recognized, as well as a reserve within accrued expenses on the condensed consolidated balance sheets. Product returns have been immaterial to date and are expected to remain immaterial in the future. The Company will update its estimated refund liability, on at least a quarterly basis, based on actual shipments of ZULRESSO subject to contractual return rights, changes in expectations about the amount of estimated refunds or actual returns. Collaborative Arrangements The Company analyzes its collaboration arrangements to assess whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities and therefore within the scope of ASC Topic 808, Collaborative Arrangements For collaboration arrangements that are within the scope of Topic 808, the Company evaluates the income statement classification for presentation of amounts due from or owed to other participants associated with multiple activities in a collaboration arrangement based on the nature of each separate activity. Payments or reimbursements that are the result of a collaborative relationship instead of a customer relationship, such as co-development and co-commercialization activities, are recorded as research and development expense or selling, general and administrative expense, in the event of a payment to the collaborative partner in a period, or a reduction to these expense line items in the event of a reimbursement from the collaboration partner in a period, as appropriate. Fair Value Measurements Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Financial assets and liabilities carried at fair value are classified and disclosed in one of the following three categories: Level 1 — Quoted market prices in active markets for identical assets or liabilities. Level 2 — Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The Company’s cash equivalents and marketable securities at September 30, 2021 and December 31, 2020 were carried at fair value, determined according to the fair value hierarchy; see Note 3, Fair Value Measurements The carrying amounts reflected in the condensed consolidated balance sheets for the collaboration receivable – related party, accounts payable and accrued expenses approximate their fair values due to their short-term maturities at September 30, 2021 and December 31, 2020, respectively. Recently Issued Accounting Pronouncements In December 2019, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. Income Taxes investments, changes from a subsidiary to an equity method investment, interim-period accounting for enacted changes in tax law, and the year-to-date loss limitation in interim-period tax accounting. The Company adopted the standard on the required effective date of January 1, 2021. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures . Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s condensed consolidated financial statements upon adoption.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The Company’s cash equivalents are classified within Level 1 and Level 2 of the fair value hierarchy. The Company’s investments in marketable securities are classified within Level 2 of the fair value hierarchy. The fair values of the Company’s marketable securities are based on prices obtained from independent pricing sources. Consistent with the fair value hierarchy described in Note 2, Summary of Significant Accounting Policies The following tables summarize the Company’s cash equivalents and marketable securities as of September 30, 2021 and December 31, 2020. September 30, 2021 Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in thousands) Cash equivalents: Cash equivalents $ 422,165 $ 421,570 $ 595 $ — Total cash equivalents 422,165 421,570 595 — Marketable securities: U.S. government securities 302,022 — 302,022 — U.S. corporate bonds 560,945 — 560,945 — International corporate bonds 238,316 — 238,316 — U.S. commercial paper 120,129 — 120,129 — International commercial paper 198,592 — 198,592 — U.S. municipal securities 1,000 — 1,000 — Total marketable securities 1,421,004 — 1,421,004 — $ 1,843,169 $ 421,570 $ 1,421,599 $ — December 31, 2020 Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in thousands) Cash equivalents: Cash equivalents $ 1,661,082 $ 1,637,609 $ 23,473 $ — Total cash equivalents 1,661,082 1,637,609 23,473 — Marketable securities: U.S. government securities 160,588 — 160,588 — U.S. corporate bonds 123,107 — 123,107 — International corporate bonds 57,676 — 57,676 — U.S. commercial paper 45,963 — 45,963 — International commercial paper 51,133 — 51,133 — Total marketable securities 438,467 — 438,467 — $ 2,099,549 $ 1,637,609 $ 461,940 $ — During the nine months ended September 30, 2021 and 2020, there were no transfers among the Level 1, Level 2 and Level 3 categories. The following tables summarize the gross unrealized gains and losses of the Company’s marketable securities as of September 30, 2021 and December 31, 2020: September 30, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Credit Losses Fair Value (in thousands) Assets: U.S. government securities $ 302,080 $ 8 $ (66 ) $ — $ 302,022 U.S. corporate bonds 561,120 69 (244 ) — 560,945 International corporate bonds 238,376 42 (102 ) — 238,316 U.S. commercial paper 120,133 2 (6 ) — 120,129 International commercial paper 198,601 2 (11 ) — 198,592 U.S. municipal securities 1,000 — — — 1,000 $ 1,421,310 $ 123 $ (429 ) $ — $ 1,421,004 December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Credit Losses Fair Value (in thousands) Assets: U.S. government securities $ 160,589 $ 11 $ (12 ) $ — $ 160,588 U.S. corporate bonds 122,882 240 (15 ) — 123,107 International corporate bonds 57,485 200 (9 ) — 57,676 U.S. commercial paper 45,963 — — — 45,963 International commercial paper 51,133 — — — 51,133 $ 438,052 $ 451 $ (36 ) $ — $ 438,467 As of September 30, 2021, cash equivalents were comprised of money market funds and U.S. corporate bonds. As of December 31, 2020, cash equivalents were comprised of commercial paper, money market funds and U.S. treasury securities. As of September 30, 2021, all marketable securities held by the Company had remaining contractual maturities of one year or less, except for U.S. government securities, U.S. corporate bonds, international corporate bonds and a municipal security with a fair value of $486.1 million that had maturities of one to two years. As of December 31, 2020, all marketable securities held by the Company had remaining contractual maturities of one year or less, except for corporate bonds with a fair value of $5.1 million that had maturities of one to two years. All marketable securities, including those with remaining contractual maturities of more than one year, are classified as current assets on the balance sheet because they are considered to be “available for sale” and the Company can convert them into cash to fund current operations. As of September 30, 2021 , the marketable securities in a loss position had a maturity of less than one year, except for U.S. government securities, U.S. corporate bonds, and international corporate bonds with a fair value of $383.0 million, that had maturities of one to two years. As of December 31, 2020, the marketable securities in a loss position had a maturity of less than one year. There have been no impairments of the Company’s assets measured and carried at fair value during the nine months ended September 30, 2021 and the year ended December 31, 2020.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	4. Balance Sheet Components Property and Equipment, net Property and equipment, net, consists of the following: September 30, December 31, 2021 2020 (in thousands) Computer hardware and software $ 1,260 $ 2,758 Furniture and equipment 897 1,865 Leasehold improvements 5,799 9,220 7,956 13,843 Less: Accumulated depreciation (5,049 ) (7,088 ) $ 2,907 $ 6,755 Depreciation expense for the three months ended September 30, 2021 and 2020 was $0.4 million and $0.7 million, respectively. Depreciation expense for the nine months ended September 30, 2021 and 2020 was $3.8 million and $2.0 million, respectively. During the nine months ended September 30, 2021, the Company removed property and equipment that was fully-depreciated from the condensed consolidated balance sheet, resulting in a decrease of $1.8 million to the gross balance of property and equipment and accumulated depreciation. During the nine months ended September 30, 2021, the Company wrote off property and equipment related to a multi-tenant building under an operating lease for office space in Cambridge, Massachusetts, in connection with the early termination of the lease by the Company. The gross balance of property and equipment and accumulated depreciation decreased by $3.3 million. Of the decrease to the gross balance, $2.1 million was depreciated immediately upon termination of the lease, and $1.2 million had been depreciated prior to the termination of the lease. Additionally, during the nine months ended September 30, 2021, the Company wrote off property and equipment related to a different multi-tenant building under an operating lease for office space in Cambridge, Massachusetts, in connection with a sublease of a portion of the leased office space. The gross balance of property and equipment and accumulated depreciation decreased by $0.9 million. Of the decrease to the gross balance, $0.5 million was depreciated immediately upon termination of the lease, and $0.4 million had been depreciated prior to the termination of the lease. The useful life for computer hardware and software is three years, furniture and equipment is five years and leasehold improvements is the lesser of the useful life or the term of the respective lease. Accrued Expenses Accrued expenses consist of the following: September 30, December 31, 2021 2020 (in thousands) Accrued research and development costs $ 44,776 $ 34,398 Employee-related 11,393 14,769 Professional services 9,965 5,184 Other 661 500 $ 66,795 $ 54,851

Leases, Commitments and Conting

Leases, Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Leases, Commitments and Contingencies	5. Leases, Commitments and Contingencies Operating Leases The Company leases office space and certain equipment. All of the leases recorded on the condensed consolidated balance sheets are operating leases. The Company’s leases have remaining lease terms ranging from less than one year to approximately three years. Some of the leases include options to extend the leases for up to five years. These options were not included for the purpose of determining the right-of-use assets and associated lease liabilities as the Company determined that the renewal of these leases is not reasonably certain so only the original lease term was taken into consideration. The leases do not include any restrictions or covenants that had to be accounted for under the lease guidance. As of January 1, 2020, the Company leased office space in three multi-tenant buildings in Cambridge, Massachusetts, consisting of 63,017 square feet in the first building, under an operating lease that will expire on August 31, 2024; 40,419 square feet in the second building, under an operating lease that will expire on August 31, 2024; and 15,975 square feet in the third building, under an operating lease that was to expire on February 29, 2024; and in a multi-tenant building in Raleigh, North Carolina, consisting of 15,525 square feet under an operating lease that will expire on November 30, 2024. During the three months ended March 31, 2021, the Company terminated the operating lease for office space in the third building in Cambridge, Massachusetts and the remaining right-of-use asset of $3.7 million and the associated liabilities related to this lease were de-recognized upon termination of the lease. During the three months ended June 30, 2021, the Company entered into a sublease for a portion of the leased office space in the second building in Cambridge, Massachusetts. From June 2018 to January 2019, the Company entered into leases for vehicles for field-based employees. These leases were determined to be operating leases and a right-of-use operating asset in the amount of $5.3 million was recorded on the balance sheet upon implementation of the new lease standard on January 1, 2019. The leases were for a term of three years and were to expire on various dates through January 31, 2022. During the three months ended June 30, 2020, these leases were terminated as part of the April 2020 restructuring, and the remaining right-of-use asset of $2.3 million and the associated liabilities related to these leases were de-recognized upon termination of the leases. During the three months ended December 31, 2020, the restricted cash of $0.7 million related to these leases was returned to the Company by the lessor. License Agreements CyDex License Agreement In September 2015, the Company and CyDex Pharmaceuticals, Inc. (“CyDex”), a wholly owned subsidiary of Ligand Pharmaceuticals, Inc., amended and restated their existing commercial license agreement. Under the terms of the commercial license agreement as amended and restated, CyDex has granted to the Company an exclusive license to CyDex’s Captisol drug formulation technology and related intellectual property for the manufacture of pharmaceutical products incorporating brexanolone and the Company’s compound known as SAGE-689, and the development and commercialization of the resulting products in the treatment, prevention or diagnosis of any disease or symptom in humans or animals other than (i) the ocular treatment of any disease or condition with a formulation, including a hormone; (ii) topical ocular treatment of inflammatory conditions; (iii) treatment and prophylaxis of fungal infections in humans; and (iv) any ocular treatment for retinal degeneration. The Company is required to pay a royalty to CyDex on sales of brexanolone and will be required to pay a royalty on any sales of SAGE-689, if such product candidate is successfully developed in the future Under the amended and restated license agreement with CyDex, the Company agreed to make milestone payments on the achievement of clinical development and regulatory milestones in the amount of up to $0.8 million in clinical milestones and up to $3.8 million in regulatory milestones for each of the first two fields with respect to brexanolone; up to $1.3 million in clinical milestones and up to $8.5 million in regulatory milestones for each of the third and fourth fields with respect to brexanolone; and up to $0.8 million in clinical milestones and up to $1.8 million in regulatory milestones for one field with respect to SAGE-689. As of September 30, 2021, the Company has recorded research and development expense and made cash payments of $3.7 million related to these clinical development and regulatory milestones and has recorded an intangible asset and made a cash payment of $3.0 million related to these regulatory milestones. For the three and nine months ended September 30, 2021, an additional clinical development milestone was met under the license agreement with CyDex related to SAGE-689, and accordingly, the Company recorded research and development expense and made a cash payment of $0.1 million For the nine months ended September 30, 2020, the Company did not record any expense or intangible asset, or make any milestone payments related to clinical development or regulatory milestones for the brexanolone program or SAGE-689 under the license agreement with CyDex. University of California License Agreements In October 2013, the Company entered into a non-exclusive license agreement with the Regents of the University of California (“the Regents”) under which the Company was granted a non-exclusive license to certain clinical data and clinical material related to brexanolone for use in the development and commercialization of biopharmaceutical products in the licensed field, including status epilepticus and postpartum depression. In May 2014, the license agreement was amended to add the treatment of essential tremor to the licensed field of use, materials and milestone fee provisions of the agreement. The Company paid to the Regents clinical development milestones of $0.1 million, prior to December 31, 2015; no other milestones are outstanding under this non-exclusive license agreement. The Company is required to pay royalties of less than 1% on net sales for a period of fifteen years following the sale of the first product developed using the data and materials. The license will terminate on the earlier to occur of (i) 27 years after the effective date or (ii) 15 years after the last-derived product is first commercially sold. In June 2015, the Company entered into an exclusive license agreement with the Regents whereby the Company was granted an exclusive license to certain patent rights related to the use of allopregnanolone to treat various diseases. In exchange for such license, the Company paid an upfront payment of $50,000 and will make payments of $15,000 for annual maintenance fees until the calendar year following the first sale, if any, of a licensed product. The Company is obligated to make milestone payments following the achievement of specified regulatory and sales milestones of up to $0.7 million and $2.0 million in the aggregate, respectively. The Company pays royalties at a low single digit percentage of net sales of ZULRESSO, subject to specified minimum annual royalty amounts. Unless terminated by operation of law or by acts of the parties under the terms of the agreement, the license agreement will terminate when the last-to-expire patents or last-to-be abandoned patent applications expire, whichever is later. As of September 30, 2021, the Company has recorded research and development expense and made cash payments of $0.3 million related to these regulatory and sales milestones; and has recorded an intangible asset and made a cash payment of $0.5 million related to these regulatory and sales milestones. For the nine months ended September 30, 2021 and 2020, the Company did not record any expense or make any milestone payments under the license agreements with the Regents. Washington University License Agreement In November 2013, the Company entered into a license agreement with Washington University whereby the Company was granted an exclusive, worldwide license under certain patent and other intellectual property rights related to SAGE-689. In exchange for these rights, the Company paid an upfront, non-refundable payment of $50,000 and, as amended in July 2021, is required to pay an annual license maintenance fee of $25,000 on each subsequent anniversary date until the first commercial sale, if any, of a licensed product. The Company is obligated to make milestone payments to Washington University based on achievement of clinical development and regulatory milestones of up to $0.7 million and $0.5 million, respectively. Additionally, the Company fulfilled its obligation to issue to Washington University 47,619 shares of common stock on December 13, 2013. The fair value of these shares of $0.1 million was recorded as research and development expense in 2013. As of September 30, 2021, the Company has recorded research and development expense and made cash payments of $0.2 million related to these clinical development milestones. The Company is obligated to pay royalties to Washington University at rates in the low single digits on net sales of licensed products covered under patent rights and royalties at rates in the low single digits on net sales of licensed products not covered under patent rights. Additionally, the Company has the right to sublicense and is required to make payments at varying percentages of sublicensing revenue received, initially in the mid-teens and descending to the mid-single digits over time. For the three and nine months ended September 30, 2021, an additional clinical development milestone was met under the license agreement with Washington University, and accordingly, the Company recorded research and development expense and made a cash payment of $0.1 million For the nine months ended September 30, 2020, the Company did not record any expense or make any milestone payments under the license agreement with Washington University.

Collaboration Agreements

Collaboration Agreements	9 Months Ended
	Sep. 30, 2021
Shionogi Collaboration Agreement [Member]
Collaboration Agreements	6. Collaboration Agreements Shionogi In June 2018 Under the terms of the collaboration agreement, Shionogi is responsible for all clinical development and regulatory filings for zuranolone in MDD and other indications in the Shionogi Territory and would be responsible for commercialization in the Shionogi Territory, if zuranolone is successfully developed and obtains marketing approval in any of the countries within the Shionogi Territory. Shionogi was required to make an upfront payment to the Company of $90.0 million, and the Company will be eligible to receive additional payments of up to $485.0 million if certain regulatory and commercial milestones are achieved by Shionogi. The potential future milestone payments include up to $70.0 million for the achievement of specified regulatory milestones, up to $30.0 million for the achievement of specified commercialization milestones, and up to $385.0 million for the achievement of specified net sales milestones. The Company is eligible to receive tiered royalties on sales of zuranolone in the Shionogi Territory, if development efforts are successful, with tiers averaging in the low to mid- twenty percent range, subject to other terms of the agreement. Shionogi has also granted to the Company certain rights to co-promote zuranolone in Japan. The Company maintains exclusive rights to develop and commercialize zuranolone outside of the Shionogi Territory . The upfront cash payment and any payments for milestones and royalties are non-refundable and non-creditable. Due to the uncertainty of pharmaceutical development and the high historical failure rates generally associated with drug development, the Company may not receive any milestone payments or any royalty payments from Shionogi. The Company concluded that Shionogi meets the definition to be accounted for as a customer because the Company is delivering intellectual property and know-how rights for the zuranolone program in support of territories in which the parties are not jointly sharing the risks and rewards. In addition, the Company determined that the Shionogi collaboration met the requirements to be accounted for as a contract, including that it was probable that the Company will collect the consideration to which the Company was entitled in exchange for the goods or services that will be delivered to Shionogi. In determining the appropriate amount of revenue to be recognized under Topic 606, the Company performed the following steps: (i) identified the promised goods or services in the contract; (ii) determined whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measured the transaction price, including the constraint on variable consideration; (iv) allocated the transaction price to the performance obligations; and (v) recognized revenue when (or as) the Company satisfied each performance obligation. The Company determined that the performance obligations in the Shionogi collaboration agreement included the license to zuranolone and the supply of certain materials during the clinical development phase, which includes the supply of active pharmaceutical ingredient (“API”). The performance obligation related to the license to zuranolone was determined to be distinct from other performance obligations and therefore was a separate performance obligation for which control was transferred upon signing. The obligation to provide certain clinical materials, including API for use during the development period, was determined to be a separate performance obligation. Given that Shionogi is not obligated to purchase any minimum amount or quantities of commercial API, the supply of API to Shionogi for commercial use was determined to be an option for Shionogi, rather than a performance obligation of the Company at contract inception and will be accounted for if and when exercised. The Company also determined that there was no separate material right in connection with the supply of API for commercial use as the expected pricing was not at a discount. Given this fact pattern, the Company has concluded the agreement has two performance obligations. Under the clinical supply agreement, the Company will manufacture and supply to Shionogi (i) clinical quantities of API reasonably required by Shionogi for the development of licensed products in the Shionogi territory under the collaboration and license agreement and (ii) quantities of drug product reasonably required for use by Shionogi in Phase 1 clinical trials of zuranolone in the Shionogi territory under the collaboration and license agreement, in the quantities agreed to by the parties. Collaboration revenue from the clinical supply agreement, which excludes the $90.0 million upfront payment, pertains to the clinical material sold under the terms of the clinical supply agreement. The Company records the costs related to the clinical supply agreement in research and development expense on its condensed consolidated statements of operations and comprehensive loss. For the nine months ended September 30, 2021 and 2020, the Company recognized no collaboration revenue from the Company’s agreement with Shionogi. The Company completed the evaluation of the standalone selling prices of each of the performance obligations and determined that the standalone selling price of the license performance obligation was $90.0 million. The Company recognized the transaction price allocated to the license performance obligation of $90.0 million as revenue during the quarter upon delivery of the license to Shionogi and resulting ability of Shionogi to use and benefit from the license, which was in the three months ended June 30, 2018. The remaining transaction price related to the performance obligation for the supply of certain clinical material is not significant. The potential milestone payments that the Company is eligible to receive were excluded from the transaction price, as all milestone amounts were fully constrained based on the probability of achievement. The Company will re-evaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, if necessary, adjust its estimate of the transaction price. Biogen In November 2020, the Company entered into the Biogen Collaboration Agreement to jointly develop and commercialize SAGE-217 products for MDD, PPD and other disorders and SAGE-324 products for essential tremor and other disorders. Concurrently, the Company also entered into a stock purchase agreement with BIMA (the “Biogen Stock Purchase Agreement”) to purchase shares of the Company’s common stock. The Biogen Collaboration Agreement became effective on December 28, 2020 (the “Effective Date”). Under the terms of the Biogen Collaboration Agreement, the Company granted Biogen co-exclusive licenses to develop and commercialize SAGE-217 products and SAGE-324 products (each, a “Product Class” and together, the “Licensed Products”) in the U.S., an exclusive license to develop and commercialize SAGE-217 products in all countries of the world other than the U.S. and the Shionogi Territory, and an exclusive license to develop and commercialize SAGE-324 products in all countries of the world other than the U.S. The Company refers to the territories outside the U.S. to which Biogen has rights under the Biogen Collaboration Agreement with respect to the applicable Licensed Product as the “Biogen Territory”. In connection with the effectiveness of the Biogen Collaboration Agreement and the closing of the sale of shares to BIMA in December 2020, the Company received $1.5 billion in consideration, comprised of an upfront payment of $875.0 million and the $650.0 million purchase price for 6,241,473 newly issued shares of the Company’s common stock (the “Biogen Shares”). As a result of the purchase of the Biogen Shares, Biogen has become a related party of the Company. The Company is eligible to receive additional payments of up to $1.6 billion if certain regulatory and commercial milestones are achieved. The potential future milestone payments for SAGE-217 products include up to $475.0 million for the achievement of specified regulatory and commercial milestones and up to $300.0 million for the achievement of specified net sales milestones. The potential future milestone payments for SAGE-324 products include up to $520.0 million for the achievement of specified regulatory and commercial milestones and up to $300.0 million for the achievement of specified net sales milestones. The Company is also eligible to receive tiered royalties on net sales of SAGE-217 products and SAGE-324 products in the Biogen Territory at percentage rates ranging from the high teens to low twenties. Due to the uncertainty of pharmaceutical development and the high historical failure rates generally associated with drug development, the Company may never receive any milestone payments or any royalty payments under the Biogen Collaboration Agreement. Development and commercialization activities in the U.S. will be conducted pursuant to plans agreed to by the Company and Biogen and overseen by a joint steering committee that will consist at all times of an equal number of representatives of each party. The Company and Biogen will share equally in the costs for development and commercialization, as well as the profits and losses, in the U.S., subject to the Company’s opt-out right described below. Biogen will be solely responsible for all development activities and costs related to any development and commercialization of SAGE-217 products and SAGE-324 products for the Biogen Territory, and the Company will receive royalties on any sales in the Biogen Territory, as mentioned above. The Company will supply API and bulk drug product for the Biogen Territory and API and final drug product for the U.S. to support development and commercialization activities. Biogen has the right to assume manufacturing responsibilities for API for the Biogen Territory at any time during the term of the agreement and will, within a reasonable period of time after the Effective Date, assume manufacturing responsibility for bulk drug product for the Biogen Territory. Unless terminated earlier, the Biogen Collaboration Agreement will continue on a Licensed Product-by-Licensed Product and country-by-country basis until the date on which (a) in any country in the Biogen Territory, the royalty term has expired for all Licensed Products in a Product Class in such country, and (b) for the U.S., the parties agree to permanently cease to commercialize all Licensed Products in a Product Class. Biogen also has the right to terminate the Biogen Collaboration Agreement for convenience in its entirety, on a Product Class-by-Product Class basis or as to a particular region, upon advance written notice. The Company has an opt-out right to convert the co-exclusive licenses in the U.S. to an exclusive license to Biogen on a Product Class-by-Product Class basis. Following the exercise of the opt-out right, the Company would no longer share equally in the profits and losses in the U.S. and would be entitled to receive certain royalty payments at percentage rates ranging from the high teens to low twenties and additional sales milestones. The Company concluded that the Biogen Collaboration Agreement and the Biogen Stock Purchase Agreement should be combined and treated as a single arrangement for accounting purposes as the agreements were entered into contemporaneously and in contemplation of one another. The Company determined that the combined agreements had elements that were within the scope of Topic 606 and Topic 808. As of the Effective Date, the Company identified the following promises in the Biogen Collaboration Agreement that were evaluated under the scope of Topic 606: delivery of (i) a co-exclusive license for SAGE-217 products in the U.S.; (ii) an exclusive license for SAGE-217 products in the Biogen Territory; (iii) a co-exclusive license for SAGE-324 products in the U.S.; (iv) an exclusive license for SAGE-324 products in the Biogen Territory; (v) the clinical manufacturing supply of API and bulk drug product for SAGE-217 products in the Biogen Territory; and (vi) the clinical manufacturing supply of API and bulk drug product for SAGE-324 products in the Biogen Territory. The Company also evaluated whether certain options outlined within the Biogen Collaboration Agreement represented material rights that would give rise to a performance obligation and concluded that none of the options convey a material right to Biogen and therefore are not considered separate performance obligations within the Biogen Collaboration Agreement. The Company assessed the above promises and determined that the co-exclusive licenses for SAGE-217 products and SAGE-324 products in the U.S. are reflective of a vendor-customer relationship and therefore represent performance obligations within the scope of Topic 606. The co-exclusive license for SAGE-217 products and SAGE-324 products in the U.S. are considered functional intellectual property and distinct from other promises under the contract. The exclusive licenses for SAGE-217 products and SAGE-324 products in the Biogen Territory are considered functional licenses that are distinct in the context of the Biogen Collaboration Agreement as Biogen can benefit from the licenses on its own or together with other readily available resources. As the co-exclusive licenses in the U.S. and the exclusive licenses in the Biogen Territory are delivered at the same time, they are considered one performance obligation at contract inception. The clinical manufacturing supply of API and bulk drug product for SAGE-217 products and SAGE-324 products for the Biogen Territory are considered distinct in the context of the Biogen Collaboration Agreement as Biogen can benefit from the manufacturing services together with the licenses transferred by the Company at the inception of the agreement. Therefore, each represents a separate performance obligation within a contract with a customer under the scope of Topic 606 at contract inception. The Company considers the collaborative activities associated with the co-development, co-commercialization, and co-manufacturing of SAGE-217 products and SAGE-324 products in the U.S. to be separate units of account within the scope of Topic 808 as the Company and Biogen are both active participants in the development and commercialization activities and are exposed to significant risks and rewards that are dependent on the development and commercial success of the activities in the arrangement. The Company has determined that the supply of API and bulk drug product for the Biogen Territory and API and final drug product for the U.S. to Biogen will be classified as collaboration revenue in the condensed consolidated statements of operations and comprehensive loss. During the nine months ended September 30, 2021, there were no collaboration revenues recognized related to the Biogen Collaboration Agreement. Payments to or reimbursements from Biogen related to the co-development, co-commercialization, and co-manufacturing activities and the agreement of the parties to share equally the cost of these activities will be accounted for as an increase to or reduction of research and development expenses or selling, general and administrative expenses, depending on the nature of the activity. During the three and nine months ended September 30, 2021, the Company recorded a net reimbursement of $24.2 million and $72.6 million, respectively, for the amount due from Biogen as a reduction of the related operating expense categories in the condensed consolidated statement of operations and comprehensive loss. As of September 30, 2021, the Company recorded a Collaboration Receivable – Related Party of $24.2 million in the condensed consolidated balance sheet. During the three and nine months ended September 30, 2021, no payments were made to Biogen and the Company received $48.4 million from Biogen for the amounts due for the six months ended June 30, 2021. The following table summarizes expenses related to the Biogen Collaboration Agreement that were incurred by the Company and the related reimbursement from Biogen, reflected by category of operating expenses: Three Months Ended September 30, Nine Months Ended September 30, 2021 2021 (in thousands) Expenses related to the Biogen Collaboration Agreement incurred by Sage $ 50,950 $ 149,653 Net reimbursement from Biogen reflected in the condensed consolidated statement of operations and comprehensive loss: Research and development expenses (21,634 ) (63,843 ) Selling, general and administrative expenses (2,551 ) (8,780 ) Total net expenses related to the Biogen Collaboration Agreement in the condensed consolidated statement of operations and comprehensive loss $ 26,765 $ 77,030 The Company determined the transaction price under Topic 606 at the inception of the Biogen Collaboration Agreement to be $1.1 billion, consisting of the upfront payment of $875.0 million plus $232.5 million in excess proceeds from the equity investment under the Biogen Stock Purchase Agreement, when measured at fair value, plus future variable consideration for manufacturing supply of clinical API and bulk drug product for the Biogen Territory. The amount of variable consideration related to the future manufacturing services was not material. The Company determined that any variable consideration related to clinical development and regulatory milestones is deemed to be fully constrained and therefore excluded from the transaction price due to the high degree of uncertainty and risk associated with these potential payments, as the Company determined that it could not assert that it was probable that a significant reversal in the amount of cumulative revenue recognized will not occur. The Company also determined that royalties and sales milestones relate solely to the licenses of intellectual property and are therefore excluded from the transaction price under the sales- or usage-based royalty exception of Topic 606. Revenue related to these royalties and sales milestones will only be recognized when the associated sales occur, and relevant thresholds are met. As noted above, the Company identified three performance obligations in the Biogen Collaboration Agreement: (i) the delivery of the co-exclusive licenses for SAGE-217 products and SAGE-324 products in the U.S. and the exclusive licenses for SAGE-217 products and SAGE-324 products in the Biogen Territory; (ii) the clinical manufacturing supply of API and bulk drug product for SAGE-217 products in the Biogen Territory; and (iii) the clinical manufacturing supply of the API and bulk drug product for SAGE-324 products in the Biogen Territory. The selling price of each performance obligation in the Biogen Collaboration Agreement was determined based on the Company’s SSP with the objective of determining the price at which it would sell such an item if it were to be sold regularly on a standalone basis. The Company allocated the variable consideration related to the manufacturing obligations to the future clinical supply of SAGE-217 products and SAGE 324 products in the Biogen Territory and the remaining fixed consideration to the license obligation. The variable consideration related to the manufacturing obligations was not material. As such, the entirety of the $1.1 billion fixed consideration of the transaction price has been allocated to the transfer of the co-exclusive licenses for SAGE-217 products and SAGE-324 products in the U.S. and the exclusive licenses for SAGE-217 products and SAGE-324 products in the Biogen Territory. The Company recognizes revenue for the license performance obligations at a point in time, that is upon transfer of the licenses to Biogen. As control of these licenses was transferred on the Effective Date and Biogen could begin to use and benefit from the licenses, the Company recognized $1.1 billion of license revenue during the year ended December 31, 2020 under the Biogen Collaboration Agreement. The Company will recognize revenue for the clinical manufacturing supply obligations at a point in time, that is upon the delivery of the supply to Biogen. Accounting for the Biogen Stock Purchase Agreement In connection with the execution of the Biogen Collaboration Agreement, the Company and BIMA entered into the Biogen Stock Purchase Agreement. Pursuant to the Biogen Stock Purchase Agreement, the Company sold the Biogen Shares to BIMA at a price of approximately $104.14 per share, which represented a 40 percent premium over the 30-day volume-weighted average share price as of the last trading day prior to the date the Biogen Collaboration Agreement and Biogen Stock Purchase Agreement were executed in November 2020, for aggregate consideration of $650.0 million. The sale of the shares to BIMA closed on December 31, 2020. The Biogen Stock Purchase Agreement includes certain standstill provisions, lock-up restrictions, and a voting agreement with respect to the Biogen Shares. Pursuant to the terms of the Biogen Stock Purchase Agreement, BIMA has agreed not to, and to cause its affiliates not to, directly or indirectly acquire the Company’s securities, seek or propose a tender or exchange offer or merger between the Company and Biogen, solicit proxies or consents with respect to any matter, or undertake other specified actions, in each case subject to specified conditions. The standstill restrictions terminate on the earliest of (i) a specified regulatory milestone under the Biogen Collaboration Agreement, (ii) the date one year following the termination of the Biogen Collaboration Agreement and (iii) the seventh anniversary of the Effective Date. BIMA has also agreed not to, and to cause its affiliates not to, sell or transfer any of the Biogen Shares for a period of eighteen months from the closing of the sale of the Biogen Shares and to limit sales and transfers of the Biogen Shares for an additional eighteen-month period, in each case subject to specified conditions and exceptions. The Company determined the fair value of the common shares issued using an option pricing valuation model to take into consideration the holding period restrictions. The fair value of the Company’s common stock was considered a level 2 fair value measurement within the fair value hierarchy. The most significant assumptions within the model are the Company’s stock price, the term of the restrictions and the stock price volatility, which is based upon a blend of historical and implied volatility of the Company’s stock. Based on the fair value adjustments made by management, the fair value of the shares issued was determined to be $417.5 million, which was $232.5 million less than the proceeds received from BIMA for the issuance of the Company’s common stock under the Biogen Stock Purchase Agreement. As such, the $232.5 million in excess proceeds has been included in the $1.1 billion transaction price of the Biogen Collaboration Agreement determined above .

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2021
Text Block [Abstract]
Common Stock	7. Common Stock On December 31, 2020, the Company completed the sale of 6,241,473 shares of its common stock in a private placement to BIMA at a price of approximately $104.14 per share, resulting in aggregate gross proceeds to the Company of $650.0 million. For additional information, refer to Note 6, Collaboration Agreements

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation Equity Plans On July 2, 2014, the stockholders of the Company approved the 2014 Stock Option and Incentive Plan (the “2014 Plan”), which became effective immediately prior to the completion of the Company’s IPO. The 2014 Plan provides for the grant of restricted stock awards, restricted stock units, incentive stock options and non-statutory stock options. The 2014 Plan replaced the Company’s 2011 Stock Option and Grant Plan (the “2011 Plan”). The Company no longer grants stock options or other awards under its 2011 Plan, but any stock options outstanding under the 2011 Plan remain outstanding and effective in accordance with their terms. The 2014 Plan provides for an annual increase, to be added on the first day of each fiscal year, by up to 4% of the Company’s outstanding shares of common stock as of the last day of the prior year. On January 1, 2021, 2,332,336 shares of common stock, representing 4% of the Company’s outstanding shares of common stock as of December 31, 2020, were added to the 2014 Plan. On December 15, 2016, the Board of Directors of the Company (the “Board”) approved the 2016 Inducement Equity Plan (as amended and restated, the “2016 Plan”). The 2016 Plan provides for the grant of equity awards to individuals who have not previously been an employee or a non-employee director of the Company to induce them to accept employment and to provide them with a proprietary interest in the Company. On September 20, 2018, the Board amended the 2016 Plan to increase the total number of shares reserved for issuance by 1,200,000 shares. Terms of equity grants, including vesting requirements, are determined by the Board or the Compensation Committee of the Board, subject to the provisions of the applicable plan. Stock options granted by the Company that are not performance-based are considered time-based because they generally vest based on the continued service of the grantee with the Company during a specified period following grant. These awards, when granted to employees, generally vest ratably over four years, with 25% cliff vesting at the one-year As of September 30, 2021, the total number of shares underlying outstanding awards under all equity plans was 8,644,442 and the total number of shares available for future issuance under all equity plans was 5,687,262 shares. Restricted Stock Units The table below summarizes activity relating to time-based restricted stock units and performance restricted stock units: Shares Outstanding as of December 31, 2020 957,695 Granted 420,161 Vested (218,017 ) Forfeited (153,121 ) Outstanding as of September 30, 2021 1,006,718 During the three months ended June 30, 2020, the Company granted 550,890 time-based restricted stock units to certain employees of the Company. These time-based restricted stock units will vest over two years, with 25% vesting at the one-year anniversary of the grant date and 75% vesting at the two-year anniversary of the grant date, which was in April 2021 and will be in April 2022 , respectively. During the three months ended June 30, 2021 , 113,941 time-based restricted stock units vested , and the fair value of th e restricted stock units that vested was $8.8 million . During the nine months ended September 30, 2021, the Company granted no time-based restricted stock units. During the three months ended September 30, 2021 and 2020, the Company granted 47,040 and 11,800 performance restricted stock units to employees of the Company, respectively; and during the nine months ended September 30, 2021 and 2020, the Company granted 420,161 and 444,616 performance restricted stock units to employees of the Company, respectively. The performance restricted stock units granted during the nine months ended September 30, 2021 are related to the achievement of a certain regulatory development milestone related to product candidates and commercial milestones. The performance restricted stock units granted during the nine months ended September 30, 2020 are related to the achievement of certain clinical development milestones related to product candidates and commercial milestones. Recognition of stock-based compensation expense associated with performance restricted stock units commences when the performance condition is considered probable of achievement, using management’s best estimates, which consider the inherent risk and uncertainty regarding the future outcomes of the milestones. During the three months ended June 30, 2021, one milestone for outstanding performance restricted stock units was achieved. T he fair value of the performance restricted stock units that vested upon achievement was $6.1 million and the Company recognized stock-based compensation expense related to this milestone of $3.8 million. 39 of the performance restricted stock units that were granted during the year ended December 31, 2020 included this milestone as a vesting condition. During the three months ended September 30, 2021, the Company considered probable the achievement of a specific clinical milestone which was the criteria for vesting of certain performance restricted stock units but which had not been met as of September 30, 2021. Therefore, $12.6 million of stock-based compensation expense was recognized related to these awards for the three months ended September 30, 2021 . Performance restricted stock units with this milestone were granted during the years ended December 31, 2020 and 2019 . No performance restricted stock units vested during the three months ended September 30, 2021 and the nine months ended September 30, 2020. At September 30, 2021, 1,006,718 time-based restricted stock units and performance restricted stock units were both outstanding and unvested, and the total unrecognized stock-based compensation expense related to these awards was $64.7 million. Of that amount, $12.6 million was recognized during the three months ended September 30, 2021 for the milestone that was considered probable. Stock Option Rollforward The table below summarizes activity related to time-based and performance-based stock options: Shares Weighted Average Exercise Price Weighted Average Remaining Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2020 7,157,830 $ 91.41 6.91 $ 167,242 Granted 1,967,133 $ 82.14 Exercised (271,430 ) $ 43.95 Forfeited (1,215,809 ) $ 121.85 Outstanding as of September 30, 2021 7,637,724 $ 85.86 6.90 $ 20,583 Exercisable as of September 30, 2021 4,344,625 $ 84.79 5.58 $ 19,215 At September 30, 2021, the Company had unrecognized stock-based compensation expense related to its unvested time-based stock option awards of $115.8 million, which is expected to be recognized over the remaining weighted average vesting period of 2.25 years. The intrinsic value of stock options exercised during the nine months ended September 30, 2021 and 2020 was $8.0 million and $0.9 million, respectively. Performance-Based Stock Options Recognition of stock-based compensation expense associated with performance-based stock options commences when the performance condition is considered probable of achievement, using management’s best estimates, which consider the inherent risk and uncertainty regarding the future outcomes of the milestones. During the three months ended March 31, 2021, in connection with the hiring of its chief executive officer, the Company granted to its chief executive officer 650,000 stock options to purchase shares of common stock that contain performance-based vesting criteria which will vest upon the achievement of certain regulatory and commercial milestones During the year ended December 31, 2020, the Company granted no stock options to employees to purchase shares of common stock that contained performance-based vesting criteria. As of September 30, 2021 and 2020, for performance-based stock option grants that were outstanding, the achievement of the milestones that had not been met that are the criteria for vesting of performance-based stock options was considered not probable, and therefore no expense has been recognized related to these awards in the nine months ended September 30, 2021 and 2020, respectively. As of September 30, 2021, 908,726 performance-based stock options were both outstanding and unvested, and the total unrecognized stock-based compensation expense related to these awards was $26.2 million. Stock-Based Compensation Expense Stock-based compensation expense recognized during the three and nine months ended September 30, 2021 and 2020 was as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in thousands) Research and development $ 17,864 $ 9,927 $ 40,598 $ 32,270 Selling, general and administrative 16,478 10,181 43,383 41,192 Restructuring — — — 1,788 $ 34,342 $ 20,108 $ 83,981 $ 75,250 Stock-based compensation expense recognized during the three and nine months ended September 30, 2021 and 2020 by award type was as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in thousands) Stock options $ 19,516 $ 18,797 $ 60,740 $ 72,434 Restricted stock units 14,563 1,066 22,538 1,815 Employee stock purchase plan 263 245 703 1,001 $ 34,342 $ 20,108 $ 83,981 $ 75,250 The stock-based compensation expense recorded for the restructuring in the nine months ended September 30, 2020 is the incremental amount related to modifying the exercise period for outstanding, vested option grants that had been made to employees whose employment was terminated in the restructuring. The weighted average grant date fair value per share of stock options granted under the Company’s stock option plans during the nine months ended September 30, 2021 and 2020 was $53.42 and $37.04, respectively.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	9. Net Loss Per Share Basic and diluted net loss per share was calculated as follows for the three and nine months ended September 30, 2021 and 2020: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Basic net loss per share: Numerator: Net loss (in thousands) $ (130,171 ) $ (105,735 ) $ (333,180 ) $ (368,822 ) Denominator: Weighted average common stock outstanding —basic 58,819,548 51,981,468 58,593,743 51,938,923 Dilutive effect of shares of common stock equivalents resulting from common stock options and restricted stock units — — — — Weighted average common stock outstanding —diluted 58,819,548 51,981,468 58,593,743 51,938,923 Net loss per share—basic and diluted $ (2.21 ) $ (2.03 ) $ (5.69 ) $ (7.10 ) The following common stock equivalents outstanding as of September 30, 2021 and 2020 were excluded from the calculation of diluted net loss per share for the periods presented because including them would have been anti-dilutive: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Stock options 6,728,998 6,945,435 6,728,998 6,945,435 Restricted stock units 310,418 489,495 310,418 489,495 Employee stock purchase plan 15,437 16,396 15,437 16,396 7,054,853 7,451,326 7,054,853 7,451,326 Stock options and restricted stock units that are outstanding and contain performance-based vesting criteria for which the performance conditions have not been met are excluded from the calculation of common stock equivalents outstanding.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The condensed consolidated financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2020, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. The condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements. In the opinion of the Company’s management, the accompanying condensed consolidated financial statements contain all adjustments, consisting of only normal recurring adjustments, necessary for a fair statement of its financial position as of September 30, 2021, its results of operations and comprehensive loss for the three and nine months ended September 30, 2021 and 2020, its cash flows for the nine months ended September 30, 2021 and 2020, and its statements of changes in stockholders’ equity for the three and nine months ended September 30, 2021 and 2020. The consolidated balance sheet at December 31, 2020 was derived from audited financial statements, but does not include all disclosures required by GAAP. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of the results for the year ending December 31, 2021, or for any future period.
Principles of Consolidation	Principles of Consolidation The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries as disclosed in Note 2, Summary of Significant Accounting Policies
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The full extent to which the COVID-19 pandemic may directly or indirectly impact the Company’s business, results of operations and financial condition, including sales, expenses, reserves and allowances, manufacturing, clinical trials, research and development costs and employee-related amounts, will depend on future developments that are highly uncertain, including: the scope and duration of the pandemic; the effectiveness of vaccination campaigns, vaccine mandates, and other efforts to control the pandemic; the duration of the vaccines’ efficacy against COVID-19 and its variants; the duration and severity of any restrictive measures taken to curb the spread of COVID-19; and the impact of the pandemic on the Company’s customers and vendors. The Company has made estimates of the impact of the COVID-19 pandemic within its condensed consolidated financial statements. Due to the evolving nature of the COVID-19 pandemic, and the emergence of highly contagious variants, there may be changes to those estimates in future periods, and a
Risks and Uncertainties	Risks and Uncertainties The product candidates developed by the Company require approvals from the U.S. Food and Drug Administration (“FDA”) or foreign regulatory agencies prior to commercial sales. There can be no assurance that the current and future product candidates of the Company will receive the necessary approvals. If the Company
Research and Development Costs and Accruals	Research and Development Costs and Accruals Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries and benefits, overhead costs, depreciation, contract services and other related costs. Research and development costs are expensed to operations as the related obligation is incurred. The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the U.S. These agreements are generally cancelable, and related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research and development costs. When billing terms under these contracts do not coincide with the timing of when the work is performed, the Company is required to make estimates of outstanding obligations to those third parties as of the end of the reporting period
Revenue Recognition	Revenue Recognition The Company generates revenue from the sale of ZULRESSO, which was approved by the FDA in March 2019 and the Company subsequently began selling in June 2019, and from collaboration and supply agreements with the Company’s collaborators. To date, revenue from collaboration agreements has come from initial, upfront payments allocated to licenses of intellectual property delivered to the Company’s collaborators and from the supply of material for clinical trials under a supply agreement Under Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: ( i ) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price, including variable consideration, if any; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, they are considered performance obligations. The exercise of a material right may be accounted for as a contract modification or as a continuation of the contract for accounting purposes. For contracts determined to be within the scope of Topic 606, the Company assesses whether the goods or services promised within each contract are distinct to identify those that are performance obligations. This assessment involves subjective determinations and requires management to make judgments about the individual promised goods or services and whether such are separable from the other aspects of the contractual relationship. Promised goods and services are considered distinct provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. The Company allocates the transaction price (the amount of consideration it expects to be entitled to from a customer in exchange for the promised goods or services) to each performance obligation and recognizes the associated revenue when (or as) each performance obligation is satisfied. The Company’s estimate of the transaction price for each contract includes all variable consideration to which the Company expects to be entitled. Collaboration and License Revenue In assessing whether a promised good or service is distinct in the evaluation of a collaboration or license arrangement subject to Topic 606, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner, and the availability of the associated expertise in the general marketplace. The Company also considers the intended benefit of the contract in assessing whether a promised good or service is separately identifiable from other promises in the contract. If a promised good or service is not distinct, the Company is required to combine that good or service with other promised goods or services until it identifies a bundle of goods or services that is distinct. The transaction price is then determined and allocated to the identified performance obligations in proportion to their standalone selling prices (“SSP”) on a relative SSP basis. SSP is determined at contract inception and is not updated to reflect changes between contract inception and when the performance obligations are satisfied. Determining the SSP for performance obligations requires significant judgment. In developing the SSP for a performance obligation, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. In certain circumstances, the Company may apply the residual method to determine the SSP of a good or service if the standalone selling price is considered highly variable or uncertain. The Company validates the SSP for performance obligations by evaluating whether changes in the key assumptions used to determine the SSP will have a significant effect on the allocation of arrangement consideration between multiple performance obligations. If the consideration promised in a contract includes a variable amount, the Company estimates the amount of consideration to which it will be entitled in exchange for transferring the promised goods or services to a customer. The Company determines the amount of variable consideration by using the expected value method or the most likely amount method. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment. If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company assessed its arrangements with Shionogi and Biogen and concluded that a significant financing component does not exist for either arrangement. For arrangements with licenses of intellectual property that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes royalty revenue and sales-based milestones at the later of (i) when the related sales occur, or (ii) when the performance obligation to which the royalty has been allocated has been satisfied. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied at a point in time or over time, and if over time this is based on the use of an output or input method. Revenue from the Company’s collaboration agreement with Shionogi has come from initial, upfront consideration upon execution of the agreement and for the supply of drug product for Shionogi’s clinical trials. Revenue from the Company’s collaboration agreement with Biogen has come from initial, upfront consideration related to the execution of the Biogen Collaboration Agreement. For additional information, refer to Note 6, Collaboration Agreements Product Revenue, Net The Company recognizes product revenues, net of variable consideration related to certain allowances and accruals that are determined using the expected value method, in its condensed consolidated financial statements at the point in time when control transfers to the customer, which is typically when the product has been delivered to the customer’s location. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. The Company’s only performance obligation identified for ZULRESSO is to deliver the product to the location specified by the customer’s order. The Company records shipping and handling costs associated with delivery of product to its customers within selling, general and administrative expenses on its condensed consolidated statements of operations and comprehensive loss. The Company expenses incremental costs of obtaining a contract as incurred if the expected amortization period of the asset would be less than one year. If the Company were to incur incremental costs with an amortization period greater than a year, such costs would be capitalized as contract assets, as they are expected to be recovered, and would be expensed by amortizing on a systematic basis that is consistent with the transfer to the customer of the goods or services to which the asset relates. The Company did not have any contract assets (unbilled receivables) at September 30, 2021, as customer invoicing generally occurs before or at the time of revenue recognition. The Company did not have any contract liabilities at September 30, 2021, as the Company did not receive any payments in advance of satisfying its performance obligations to its customers. Amounts billed or invoiced that are considered trade accounts receivable are included in prepaid expenses and other current assets on the condensed consolidated balance sheets. As of September 30, 2021 and December 31, 2020, the Company had not provided any allowance for bad debts against the trade accounts receivable, and the amount of trade accounts receivable was not significant. The Company records reserves, based on contractual terms, for the following components of variable consideration related to product sold during the reporting period, as well as its estimate of product that remains in the distribution channel inventory of its customers at the end of the reporting period. On a quarterly basis, the Company updates its estimates, if necessary, and records any material adjustments in the period they are identified. Chargebacks : The Company estimates chargebacks from its customers who directly purchase the product from the Company for discounts resulting from contractual commitments to sell products to eligible healthcare settings at prices lower than the list prices charged to its customers. Customers charge the Company for the difference between what they pay to the Company for the product and the selling price to the eligible healthcare settings. Reserves for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel inventories at the end of each reporting period that the Company expects will be sold to eligible healthcare settings, and chargebacks that customers have claimed, but for which the Company has not yet issued a credit. Government Rebates : The Company is subject to discount obligations under government programs, including Medicaid. The Company records reserves for rebates in the same period the related product revenue is recognized, resulting in a reduction of ZULRESSO product revenues and a current liability that is included in accrued expenses on its condensed consolidated balance sheets. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimates of future claims that will be made for product that has been recognized as revenue, but which remains in the distribution channel at the end of each reporting period. Trade Discounts and Allowances : The Company generally provides customary invoice discounts on ZULRESSO sales to its customers for prompt payment and the Company pays fees for sales order management, data, and distribution services. The Company estimates its customers will earn these discounts and fees and deducts these discounts and fees in full from gross ZULRESSO revenues and accounts receivable at the time the Company recognizes the related revenues. Financial Assistance : The Company provides voluntary financial assistance programs to patients with commercial insurance that have coverage and reside in states that allow financial assistance. The Company estimates the financial assistance amounts for ZULRESSO and records any such amounts within accrued expenses on its condensed consolidated balance sheets. The calculation of the accrual for financial assistance is based on an estimate of claims and the cost per claim that the Company expects to receive using demographics for patients who have registered and been approved for assistance. Any adjustments are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability, which is included as a component of accrued expenses on the condensed consolidated balance sheets. Product Returns : Consistent with industry practice, the Company offers product return rights to direct customers for damaged, defective or expiring product, provided it is within a specified period around the product expiration date as set forth in the Company’s return goods policy. The Company estimates the amount of its product sales that may be returned by its customers and records this estimate as a reduction of revenue in the period the related product revenue is recognized, as well as a reserve within accrued expenses on the condensed consolidated balance sheets. Product returns have been immaterial to date and are expected to remain immaterial in the future. The Company will update its estimated refund liability, on at least a quarterly basis, based on actual shipments of ZULRESSO subject to contractual return rights, changes in expectations about the amount of estimated refunds or actual returns.
Collaborative Arrangements	Collaborative Arrangements The Company analyzes its collaboration arrangements to assess whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities and therefore within the scope of ASC Topic 808, Collaborative Arrangements For collaboration arrangements that are within the scope of Topic 808, the Company evaluates the income statement classification for presentation of amounts due from or owed to other participants associated with multiple activities in a collaboration arrangement based on the nature of each separate activity. Payments or reimbursements that are the result of a collaborative relationship instead of a customer relationship, such as co-development and co-commercialization activities, are recorded as research and development expense or selling, general and administrative expense, in the event of a payment to the collaborative partner in a period, or a reduction to these expense line items in the event of a reimbursement from the collaboration partner in a period, as appropriate.
Fair Value Measurements	Fair Value Measurements Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Financial assets and liabilities carried at fair value are classified and disclosed in one of the following three categories: Level 1 — Quoted market prices in active markets for identical assets or liabilities. Level 2 — Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The Company’s cash equivalents and marketable securities at September 30, 2021 and December 31, 2020 were carried at fair value, determined according to the fair value hierarchy; see Note 3, Fair Value Measurements The carrying amounts reflected in the condensed consolidated balance sheets for the collaboration receivable – related party, accounts payable and accrued expenses approximate their fair values due to their short-term maturities at September 30, 2021 and December 31, 2020, respectively.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In December 2019, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. Income Taxes investments, changes from a subsidiary to an equity method investment, interim-period accounting for enacted changes in tax law, and the year-to-date loss limitation in interim-period tax accounting. The Company adopted the standard on the required effective date of January 1, 2021. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures . Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s condensed consolidated financial statements upon adoption.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Summary of Company's Cash Equivalents and Marketable Securities	The following tables summarize the Company’s cash equivalents and marketable securities as of September 30, 2021 and December 31, 2020. September 30, 2021 Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in thousands) Cash equivalents: Cash equivalents $ 422,165 $ 421,570 $ 595 $ — Total cash equivalents 422,165 421,570 595 — Marketable securities: U.S. government securities 302,022 — 302,022 — U.S. corporate bonds 560,945 — 560,945 — International corporate bonds 238,316 — 238,316 — U.S. commercial paper 120,129 — 120,129 — International commercial paper 198,592 — 198,592 — U.S. municipal securities 1,000 — 1,000 — Total marketable securities 1,421,004 — 1,421,004 — $ 1,843,169 $ 421,570 $ 1,421,599 $ — December 31, 2020 Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in thousands) Cash equivalents: Cash equivalents $ 1,661,082 $ 1,637,609 $ 23,473 $ — Total cash equivalents 1,661,082 1,637,609 23,473 — Marketable securities: U.S. government securities 160,588 — 160,588 — U.S. corporate bonds 123,107 — 123,107 — International corporate bonds 57,676 — 57,676 — U.S. commercial paper 45,963 — 45,963 — International commercial paper 51,133 — 51,133 — Total marketable securities 438,467 — 438,467 — $ 2,099,549 $ 1,637,609 $ 461,940 $ —
Summary of Gross Unrealized Gains and Losses of Marketable Securities	The following tables summarize the gross unrealized gains and losses of the Company’s marketable securities as of September 30, 2021 and December 31, 2020: September 30, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Credit Losses Fair Value (in thousands) Assets: U.S. government securities $ 302,080 $ 8 $ (66 ) $ — $ 302,022 U.S. corporate bonds 561,120 69 (244 ) — 560,945 International corporate bonds 238,376 42 (102 ) — 238,316 U.S. commercial paper 120,133 2 (6 ) — 120,129 International commercial paper 198,601 2 (11 ) — 198,592 U.S. municipal securities 1,000 — — — 1,000 $ 1,421,310 $ 123 $ (429 ) $ — $ 1,421,004 December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Credit Losses Fair Value (in thousands) Assets: U.S. government securities $ 160,589 $ 11 $ (12 ) $ — $ 160,588 U.S. corporate bonds 122,882 240 (15 ) — 123,107 International corporate bonds 57,485 200 (9 ) — 57,676 U.S. commercial paper 45,963 — — — 45,963 International commercial paper 51,133 — — — 51,133 $ 438,052 $ 451 $ (36 ) $ — $ 438,467

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net, consists of the following: September 30, December 31, 2021 2020 (in thousands) Computer hardware and software $ 1,260 $ 2,758 Furniture and equipment 897 1,865 Leasehold improvements 5,799 9,220 7,956 13,843 Less: Accumulated depreciation (5,049 ) (7,088 ) $ 2,907 $ 6,755
Summary of Accrued Expenses	Accrued expenses consist of the following: September 30, December 31, 2021 2020 (in thousands) Accrued research and development costs $ 44,776 $ 34,398 Employee-related 11,393 14,769 Professional services 9,965 5,184 Other 661 500 $ 66,795 $ 54,851

Collaboration Agreements (Table

Collaboration Agreements (Tables)	9 Months Ended
	Sep. 30, 2021
Collaboration Agreement [Abstract]
Summary of Operating Expenses Category Related to Collaboration Agreement	The following table summarizes expenses related to the Biogen Collaboration Agreement that were incurred by the Company and the related reimbursement from Biogen, reflected by category of operating expenses: Three Months Ended September 30, Nine Months Ended September 30, 2021 2021 (in thousands) Expenses related to the Biogen Collaboration Agreement incurred by Sage $ 50,950 $ 149,653 Net reimbursement from Biogen reflected in the condensed consolidated statement of operations and comprehensive loss: Research and development expenses (21,634 ) (63,843 ) Selling, general and administrative expenses (2,551 ) (8,780 ) Total net expenses related to the Biogen Collaboration Agreement in the condensed consolidated statement of operations and comprehensive loss $ 26,765 $ 77,030

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Activity Relating to Restricted Stock Units	The table below summarizes activity relating to time-based restricted stock units and performance restricted stock units: Shares Outstanding as of December 31, 2020 957,695 Granted 420,161 Vested (218,017 ) Forfeited (153,121 ) Outstanding as of September 30, 2021 1,006,718
Summary of Activity Relating to Time Based and Performance Based Stock Options	The table below summarizes activity related to time-based and performance-based stock options: Shares Weighted Average Exercise Price Weighted Average Remaining Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2020 7,157,830 $ 91.41 6.91 $ 167,242 Granted 1,967,133 $ 82.14 Exercised (271,430 ) $ 43.95 Forfeited (1,215,809 ) $ 121.85 Outstanding as of September 30, 2021 7,637,724 $ 85.86 6.90 $ 20,583 Exercisable as of September 30, 2021 4,344,625 $ 84.79 5.58 $ 19,215
Summary of Stock-Based Compensation Expense Recognized	Stock-based compensation expense recognized during the three and nine months ended September 30, 2021 and 2020 was as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in thousands) Research and development $ 17,864 $ 9,927 $ 40,598 $ 32,270 Selling, general and administrative 16,478 10,181 43,383 41,192 Restructuring — — — 1,788 $ 34,342 $ 20,108 $ 83,981 $ 75,250
Summary of Stock-Based Compensation Expense by Award Type	Stock-based compensation expense recognized during the three and nine months ended September 30, 2021 and 2020 by award type was as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in thousands) Stock options $ 19,516 $ 18,797 $ 60,740 $ 72,434 Restricted stock units 14,563 1,066 22,538 1,815 Employee stock purchase plan 263 245 703 1,001 $ 34,342 $ 20,108 $ 83,981 $ 75,250

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Summary of Basic and Diluted Net Loss Per Share	Basic and diluted net loss per share was calculated as follows for the three and nine months ended September 30, 2021 and 2020: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Basic net loss per share: Numerator: Net loss (in thousands) $ (130,171 ) $ (105,735 ) $ (333,180 ) $ (368,822 ) Denominator: Weighted average common stock outstanding —basic 58,819,548 51,981,468 58,593,743 51,938,923 Dilutive effect of shares of common stock equivalents resulting from common stock options and restricted stock units — — — — Weighted average common stock outstanding —diluted 58,819,548 51,981,468 58,593,743 51,938,923 Net loss per share—basic and diluted $ (2.21 ) $ (2.03 ) $ (5.69 ) $ (7.10 )
Summary of Anti-Dilutive Common Stock Equivalents Outstanding	The following common stock equivalents outstanding as of September 30, 2021 and 2020 were excluded from the calculation of diluted net loss per share for the periods presented because including them would have been anti-dilutive: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Stock options 6,728,998 6,945,435 6,728,998 6,945,435 Restricted stock units 310,418 489,495 310,418 489,495 Employee stock purchase plan 15,437 16,396 15,437 16,396 7,054,853 7,451,326 7,054,853 7,451,326

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Nature Of Business [Line Items]
Accumulated deficit	$ 1,370,674	$ 1,037,494
Net income from up-front		$ 606,100
Up-front payments receive	1,000,000
Redeemable Convertible Preferred Stock [Member] | Convertible Notes [Member] | Initial Public Offering [Member]
Nature Of Business [Line Items]
Net proceeds from sale of equity and notes	$ 2,800,000

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2021
Product Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Incremental costs incurred expected amortization period of asset	true

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Company's Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	$ 422,165	$ 1,661,082
Total marketable securities	1,421,004	438,467
Total cash equivalents and marketable securities	1,843,169	2,099,549
Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	422,165	1,661,082
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	421,570	1,637,609
Total cash equivalents and marketable securities	421,570	1,637,609
Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	421,570	1,637,609
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	595	23,473
Total marketable securities	1,421,004	438,467
Total cash equivalents and marketable securities	1,421,599	461,940
Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	595	23,473
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	302,022	160,588
U.S. Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	302,022	160,588
U.S. Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	560,945	123,107
U.S. Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	560,945	123,107
International Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	238,316	57,676
International Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	238,316	57,676
U.S. Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	120,129	45,963
U.S. Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	120,129	45,963
International Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	198,592	51,133
International Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	198,592	$ 51,133
U.S. Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	1,000
U.S. Municipal Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	$ 1,000

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Debt Instrument Fair Value Carrying Value [Line Items]
Transfers among the Level 1, Level 2 and Level 3 categories	$ 0		$ 0
Impairment of assets	0	$ 0
U.S Government Securities | U.S. Corporate Bonds [Member]
Debt Instrument Fair Value Carrying Value [Line Items]
Marketable securities fair value held to maturity		$ 5,100,000
Marketable securities loss on fair value held to maturity	383,000,000
U.S Government Securities | Corporate Bonds and Municipal Securities [Member]
Debt Instrument Fair Value Carrying Value [Line Items]
Marketable securities fair value held to maturity	$ 486,100,000
Maximum [Member] | U.S Government Securities | U.S. Corporate Bonds [Member]
Debt Instrument Fair Value Carrying Value [Line Items]
Marketable securities, remaining contractual maturities	1 year	1 year
Marketable securities held, maturity period		2 years
Maximum [Member] | U.S Government Securities | Corporate Bonds and Municipal Securities [Member]
Debt Instrument Fair Value Carrying Value [Line Items]
Marketable securities held, maturity period	2 years
Minimum [Member] | U.S Government Securities | U.S. Corporate Bonds [Member]
Debt Instrument Fair Value Carrying Value [Line Items]
Marketable securities held, maturity period		1 year
Minimum [Member] | U.S Government Securities | Corporate Bonds and Municipal Securities [Member]
Debt Instrument Fair Value Carrying Value [Line Items]
Marketable securities held, maturity period	1 year

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Gross Unrealized Gains and Losses of Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,421,310	$ 438,052
Gross Unrealized Gains	123	451
Gross Unrealized Losses	(429)	(36)
Fair Value	1,421,004	438,467
U.S. Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	302,080	160,589
Gross Unrealized Gains	8	11
Gross Unrealized Losses	(66)	(12)
Fair Value	302,022	160,588
U.S. Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	561,120	122,882
Gross Unrealized Gains	69	240
Gross Unrealized Losses	(244)	(15)
Fair Value	560,945	123,107
International Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	238,376	57,485
Gross Unrealized Gains	42	200
Gross Unrealized Losses	(102)	(9)
Fair Value	238,316	57,676
U.S. Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	120,133	45,963
Gross Unrealized Gains	2
Gross Unrealized Losses	(6)
Fair Value	120,129	45,963
International Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	198,601	51,133
Gross Unrealized Gains	2
Gross Unrealized Losses	(11)
Fair Value	198,592	$ 51,133
U.S. Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,000
Fair Value	$ 1,000

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 7,956	$ 13,843
Less: Accumulated depreciation	(5,049)	(7,088)
Property and equipment, net	2,907	6,755
Computer Hardware and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,260	2,758
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	897	1,865
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,799	$ 9,220

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 400	$ 700	$ 3,849	$ 1,981
Decrease in gross balance of property and equipment			(1,800)
Decrease in accumulated depreciation			$ (1,800)
Computer Hardware and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			3 years
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			5 years
Multi-tenant Building under Operating Lease [Member]
Property, Plant and Equipment [Line Items]
Decrease in gross balance of property and equipment			$ (3,300)
Decrease in accumulated depreciation			(1,200)
Depreciated gross balance of property and equipment	2,100		2,100
Sublease Multi Tenant Building Under Operating Lease [Member]
Property, Plant and Equipment [Line Items]
Decrease in gross balance of property and equipment			(900)
Decrease in accumulated depreciation			(400)
Depreciated gross balance of property and equipment	$ 500		$ 500

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued research and development costs	$ 44,776	$ 34,398
Employee-related	11,393	14,769
Professional services	9,965	5,184
Other	661	500
Total accrued expenses	$ 66,795	$ 54,851

Leases, Commitments and Conti_2

Leases, Commitments and Contingencies - Operating Leases - Additional Information (Detail) $ in Thousands	Jan. 01, 2020ft²	Jan. 01, 2019USD ($)ft²	Jun. 30, 2021USD ($)	Sep. 30, 2021USD ($)	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)	May 31, 2020USD ($)
Commitments And Contingencies [Line Items]
Lease expire date			Jan. 31, 2022
Operating lease option to extend			true
Operating lease renewal term			5 years
Right-of-use operating asset | $		$ 5,300		$ 17,432	$ 3,700	$ 25,064	$ 2,300
Operating lease term of contract			3 years
Restricted Cash And Cash Equivalents Noncurrent | $			$ 700
Operating Lease One [Member]
Commitments And Contingencies [Line Items]
Office space rent under operating lease		63,017
Lease expire date		Aug. 31, 2024
Operating Lease Two [Member]
Commitments And Contingencies [Line Items]
Office space rent under operating lease		40,419
Lease expire date		Aug. 31, 2024
Operating Lease Three [Member]
Commitments And Contingencies [Line Items]
Office space rent under operating lease	15,525
Lease expire date	Nov. 30, 2024
Operating Lease Five [Member]
Commitments And Contingencies [Line Items]
Office space rent under operating lease	15,975
Lease expire date	Feb. 29, 2024
Minimum [Member]
Commitments And Contingencies [Line Items]
Operating lease remaining lease terms			1 year
Maximum [Member]
Commitments And Contingencies [Line Items]
Operating lease remaining lease terms			3 years

Leases, Commitments and Conti_3

Leases, Commitments and Contingencies - CyDex License Agreement - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Commitments And Contingencies [Line Items]
Research and development expense	$ 83,497,000	$ 74,078,000		$ 207,723,000	$ 211,008,000
CyDex License Agreement [Member]
Commitments And Contingencies [Line Items]
Research and development expense				1,000,000
CyDex License Agreement [Member] | First and Second Clinical Development Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	800,000			800,000
CyDex License Agreement [Member] | First and Second Regulatory Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	3,800,000			3,800,000
CyDex License Agreement [Member] | Third and Fourth Clinical Development Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	1,300,000			1,300,000
CyDex License Agreement [Member] | Third and Fourth Regulatory Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	8,500,000			8,500,000
CyDex License Agreement [Member] | Clinical Development [Member] | Brexanolone [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense					0
Milestone payments					0
Milestone payments related to intangible assets					0
CyDex License Agreement [Member] | Clinical Development [Member] | SAGE-689 [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense	100,000			100,000
Milestone payments	100,000			100,000
CyDex License Agreement [Member] | Clinical Development [Member] | SAGE-689 [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	800,000			800,000
CyDex License Agreement [Member] | Regulatory Milestones [Member] | Brexanolone [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense					0
Milestone payments					0
Intangible asset related to milestone		$ 0			0
Milestone payments related to intangible assets					$ 0
CyDex License Agreement [Member] | Regulatory Milestones [Member] | SAGE-689 [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 1,800,000			$ 1,800,000
CyDex License Agreement [Member] | Clinical Development and Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense			$ 3,700,000
Milestone payments			3,700,000
Intangible asset related to milestone			$ 3,000,000

Leases, Commitments and Conti_4

Leases, Commitments and Contingencies - University of California License Agreements - Additional Information (Detail) - University of California License Agreements [Member] - USD ($)	Dec. 31, 2015	Jun. 30, 2015	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2015
Commitments And Contingencies [Line Items]
Upfront payment		$ 50,000
Annual license maintenance fee					$ 15,000
Research and development expense related to milestone expense			$ 0	$ 0
Milestone payments			0	$ 0
After The Effective Date [Member]
Commitments And Contingencies [Line Items]
Licenses Expiration period, maximum	27 years
After The First Sale [Member]
Commitments And Contingencies [Line Items]
Licenses Expiration period, maximum	15 years
Clinical Development [Member]
Commitments And Contingencies [Line Items]
Milestone payments	$ 100,000
Milestone outstanding	$ 0
Clinical Development [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Percentage of net sales paid as royalties	1.00%
Regulatory Milestones [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments		700,000
Sales Milestones [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments		$ 2,000,000
Regulatory and Sales Milestones [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense			300,000
Milestone payments			300,000
Intangible asset related to milestone			500,000
Milestone payments related to intangible assets			$ 500,000

Leases, Commitments and Conti_5

Leases, Commitments and Contingencies - Washington University License Agreement - Additional Information (Detail) - Washington University License Agreement [Member] - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended		12 Months Ended
	Nov. 30, 2013	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2013
Commitments And Contingencies [Line Items]
Upfront non-refundable payment	$ 50,000
Annual license maintenance fee					$ 25,000
Issuance of common stock, shares					47,619
Research and development expense related to issue of common stock obligation					$ 100,000
Research and development expense related to milestone expense		$ 100,000	$ 100,000	$ 0
Milestone payments		$ 100,000	100,000	$ 0
Clinical Development [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense			200,000
Milestone payments			$ 200,000
Maximum [Member] | Clinical Development [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	700,000
Maximum [Member] | Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 500,000

Collaboration Agreements - Addi

Collaboration Agreements - Additional Information (Detail) - USD ($)	Nov. 30, 2020	Jun. 30, 2018	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2018	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Jun. 12, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue			$ 1,440,000	$ 1,639,000		$ 4,666,000	$ 5,014,000
Number of shares issued								6,241,473
Collaboration receivable - related party			24,185,000			24,185,000
Shionogi Collaboration Agreement [Member] | Collaboration Revenue [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue						0	$ 0
Shionogi Collaboration Agreement [Member] | SAGE-217 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement effective date		Jun. 30, 2018
Upfront payment		$ 90,000,000
Average percentage on tiered royalties		20.00%
Revenue					$ 90,000,000
Standalone selling price of license performance obligation		$ 90,000,000			90,000,000
Shionogi Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payment receivable		485,000,000			$ 485,000,000
Shionogi Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member] | Regulatory Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments		70,000,000
Shionogi Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member] | Commercial Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments		30,000,000
Shionogi Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member] | Sales Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments		$ 385,000,000
Biogen Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement effective date	Dec. 28, 2020
Upfront payment								$ 875,000,000
Revenue								1,100,000,000
Standalone selling price of license performance obligation								1,100,000,000
Sale of stock, and upfront payment consideration received								$ 1,500,000,000
Number of shares issued								6,241,473
Purchase price								$ 650,000,000
Reimbursement reductions to expense			24,200,000			72,600,000
Collaboration receivable - related party			24,200,000			24,200,000
Proceeds from related parties			48,400,000			48,400,000
Payments To Related Parties			$ 0			0
Biogen Collaboration Agreement [Member] | Collaboration Revenue [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue						$ 0
Biogen Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payment receivable									$ 1,600,000,000
Biogen Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member] | Sales Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments	$ 300,000,000
Biogen Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member] | Regulatory and Commercial Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments	475,000,000
Biogen Collaboration Agreement [Member] | SAGE-324 [Member] | Maximum [Member] | Sales Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments	300,000,000
Biogen Collaboration Agreement [Member] | SAGE-324 [Member] | Maximum [Member] | Regulatory and Commercial Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments	$ 520,000,000
Biogen Stock Purchase Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment								875,000,000
Purchase price								650,000,000
Transaction price, total								1,100,000,000
Premium amount on equity investment								$ 232,500,000
Price per share								$ 104.14
Premium on per share price								40.00%
Stock issued								$ 417,500,000

Collaboration Agreements - Summ

Collaboration Agreements - Summary of Operating Expenses Category Related to Collaboration Agreement (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net reimbursement from Biogen reflected in the condensed consolidated statement of operations and comprehensive loss:
Research and development expenses	$ (83,497)	$ (74,078)	$ (207,723)	$ (211,008)
Selling, general and administrative expenses	(48,706)	(35,099)	(131,899)	(143,454)
Total operating costs and expenses	132,334	$ 108,797	340,088	$ 382,764
Biogen Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Expenses related to the Biogen Collaboration Agreement incurred by Sage	50,950		149,653
Net reimbursement from Biogen reflected in the condensed consolidated statement of operations and comprehensive loss:
Research and development expenses	(21,634)		(63,843)
Selling, general and administrative expenses	(2,551)		(8,780)
Total operating costs and expenses	$ 26,765		$ 77,030

Common Stock - Additional Infor

Common Stock - Additional Information (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)$ / sharesshares
Equity [Abstract]
Issuance of common stock, shares | shares	6,241,473
Common stock price per share | $ / shares	$ 104.14
Proceeds from public offering of common stock, net of commissions and underwriting discounts and offering costs | $	$ 650

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	Jan. 01, 2021	Jan. 01, 2019	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Sep. 20, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation granted under plan vested period							2 years	4 years
Share based compensation, vest period								1 year
Share based compensation, term of plan								10 years
Total number of shares outstanding			8,644,442					8,644,442
Common stock available for issuance under stock option plan			5,687,262					5,687,262
Restricted stock units granted							550,890	0
Restricted stock units vested				113,941
Fair value of restricted stock units vested				$ 8,800,000
Stock-based compensation expense			$ 34,342,000			$ 20,108,000		$ 83,981,000	$ 75,250,000
Outstanding and unvested restricted stock units			1,006,718					1,006,718
Weighted average grant date fair value per share								$ 53.42	$ 37.04
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted								420,161
Stock-based compensation expense			$ 14,563,000			$ 1,066,000		$ 22,538,000	$ 1,815,000
Outstanding and unvested restricted stock units			1,006,718					1,006,718		957,695
Performance Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock units vested				6,100,000					$ 0
Milestone performance restricted stock percentage										39
Total unrecognized stock-based compensation expense			$ 64,700,000					$ 64,700,000
Performance Restricted Stock Units [Member] | Commercial Milestones [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted			47,040			11,800		420,161	444,616
Stock-based compensation expense			$ 12,600,000	$ 3,800,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted								1,967,133
Total number of shares outstanding			7,637,724					7,637,724		7,157,830
Stock-based compensation expense			$ 19,516,000			$ 18,797,000		$ 60,740,000	$ 72,434,000
Total unrecognized stock-based compensation expense			115,800,000					$ 115,800,000
Weighted average period of unrecognized compensation costs								2 years 3 months
Intrinsic value of options exercised								$ 8,000,000	900,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted		0
Total unrecognized stock-based compensation expense			$ 26,200,000					$ 26,200,000
Number of shares outstanding and unvested stock options			908,726					908,726
Performance Shares [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted					650,000
Performance-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense								$ 0	$ 0
Restricted Stock Units Vest One Year Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units cliff vesting percentage								25.00%
Restricted Stock Units Vest One Year Anniversary [Member] | Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units cliff vesting percentage							25.00%
Restricted stock units vesting period month and year							2021-04
Restricted Stock Units Vest Two Year Anniversary [Member] | Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units cliff vesting percentage							75.00%
Restricted stock units vesting period month and year							2022-04
2011 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted								0
2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares annual increase added to plan	2,332,336
2014 Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of increase on outstanding shares of Common stock										4.00%
2016 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares reserved for issuance											1,200,000

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Activity Relating to Restricted Stock Units (Detail) - shares	3 Months Ended	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	550,890	0
Outstanding, Shares at ending balance		1,006,718
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, Shares at beginning balance		957,695
Granted, Shares		420,161
Vested, Shares		(218,017)
Forfeited, Shares		(153,121)
Outstanding, Shares at ending balance		1,006,718

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Activity Relating to Time Based and Performance Based Stock Options (Detail) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, Outstanding Shares	8,644,442
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Outstanding Shares	7,157,830
Granted, Shares	1,967,133
Exercised, Shares	(271,430)
Forfeited, Shares	(1,215,809)
Ending balance, Outstanding Shares	7,637,724	7,157,830
Exercisable, Shares	4,344,625
Beginning balance, Outstanding Weighted Average Exercise Price | $ / shares	$ 91.41
Granted, Weighted Average Exercise Price | $ / shares	82.14
Exercised, Weighted Average Exercise Price | $ / shares	43.95
Forfeited, Weighted Average Exercise Price | $ / shares	121.85
Ending balance, Outstanding Weighted Average Exercise Price | $ / shares	85.86	$ 91.41
Exercisable, Weighted Average Exercise Price | $ / shares	$ 84.79
Outstanding, Weighted Average Remaining Life	6 years 10 months 24 days	6 years 10 months 28 days
Exercisable, Weighted Average Remaining Life	5 years 6 months 29 days
Outstanding, Aggregate Intrinsic Value | $	$ 20,583	$ 167,242
Exercisable, Aggregate Intrinsic Value | $	$ 19,215

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 34,342	$ 20,108	$ 83,981	$ 75,250
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	17,864	9,927	40,598	32,270
Selling, General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 16,478	$ 10,181	$ 43,383	41,192
Restructuring Charges [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense				$ 1,788

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of Stock-Based Compensation Expense by Award Type Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 34,342	$ 20,108	$ 83,981	$ 75,250
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	19,516	18,797	60,740	72,434
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	14,563	1,066	22,538	1,815
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 263	$ 245	$ 703	$ 1,001

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss	$ (130,171)	$ (107,245)	$ (95,764)	$ (105,735)	$ (136,347)	$ (126,740)	$ (333,180)	$ (368,822)
Denominator:
Weighted average common stock outstanding —basic	58,819,548			51,981,468			58,593,743	51,938,923
Dilutive effect of shares of common stock equivalents resulting from common stock options and restricted stock units	0			0			0	0
Weighted average common stock outstanding —diluted	58,819,548			51,981,468			58,593,743	51,938,923
Net loss per share—basic and diluted	$ (2.21)			$ (2.03)			$ (5.69)	$ (7.10)

Net Loss Per Share - Summary _2

Net Loss Per Share - Summary of Anti-Dilutive Common Stock Equivalents Outstanding (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	7,054,853	7,451,326	7,054,853	7,451,326
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	6,728,998	6,945,435	6,728,998	6,945,435
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	310,418	489,495	310,418	489,495
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	15,437	16,396	15,437	16,396