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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2015	Feb. 16, 2016	Jun. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Trading Symbol	SAGE
Entity Registrant Name	Sage Therapeutics, Inc.
Entity Central Index Key	0001597553
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		32,022,187
Entity Public Float			$ 903,465,958

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 186,753	$ 127,766
Prepaid expenses and other current assets	1,738	1,056
Total current assets	188,491	128,822
Property and equipment, net	286	163
Restricted cash	39	39
Deferred offering costs	200
Deferred tax assets		641
Total assets	189,016	129,665
Current liabilities:
Accounts payable	5,159	2,429
Accrued expenses	10,148	4,687
Deferred tax liabilities		641
Total current liabilities	15,307	7,757
Other liabilities	14	23
Total liabilities	15,321	7,780
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized at December 31, 2015 and 2014; no shares issued or outstanding at December 31, 2015 and 2014
Common stock, $0.0001 par value; 120,000,000 shares authorized at December 31, 2015 and 2014; 28,823,549 and 25,621,791 shares issued and outstanding at December 31, 2015 and 2014, respectively	3	3
Additional paid-in capital	335,032	188,727
Accumulated deficit	(161,340)	(66,845)
Total stockholders' equity	173,695	121,885
Total liabilities and stockholders' equity	$ 189,016	$ 129,665

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
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	28,823,549	25,621,791
Common stock, shares outstanding	28,823,549	25,621,791

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating expenses:
Research and development	$ 69,357	$ 24,100	$ 14,357
General and administrative	25,293	9,710	3,922
Total operating expenses	94,650	33,810	18,279
Loss from operations	(94,650)	(33,810)	(18,279)
Interest income, net	178	8	1
Other expense, net	(23)	(9)	(3)
Net loss and comprehensive loss	(94,495)	(33,811)	(18,281)
Accretion of redeemable convertible preferred stock to redemption value		(2,294)	(7)
Net loss attributable to common stockholders	$ (94,495)	$ (36,105)	$ (18,288)
Net loss per share attributable to common stockholders-basic and diluted	$ (3.40)	$ (1.67)	$ (12.26)
Weighted average number of common shares used in net loss per share attributable to common stockholders-basic and diluted	27,778,288	21,574,347	1,492,288

Consolidated Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Initial Public Offering [Member]	Common Stock [Member]	Common Stock [Member] Initial Public Offering [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Initial Public Offering [Member]	Accumulated Deficit [Member]	Series A, B and C Redeemable Convertible Preferred Stock[Member]	Series A, B and C Redeemable Convertible Preferred Stock[Member] Series A Preferred Stock [Member]	Series A, B and C Redeemable Convertible Preferred Stock[Member] Series B Preferred Stock [Member]	Series A, B and C Redeemable Convertible Preferred Stock[Member] Series C Preferred Stock [Member]
Balance at Dec. 31, 2012	$ (13,394)						$ (13,394)	$ 14,970
Balance, Shares at Dec. 31, 2012			1,395,273						15,000,000
Issuance of common stock from exercise of stock options, Amount	1				$ 1
Shares issued during period, Amount									$ 22,732
Issuance of common stock from exercise of stock options, Shares			3,174
Shares issued during period, Shares									22,750,000
Vesting of restricted stock, Amount	20				20
Vesting of restricted stock, Shares			176,695
Accretion of redeemable convertible preferred stock to redemption value	(7)				(7)				$ 7
Issuance of common stock in payment of licensing and consultant fees, Amount	64				64
Issuance of common stock in payment of licensing and consultant fees, Shares			47,619
Stock-based compensation expense	61				61
Net loss	(18,281)						(18,281)
Balance at Dec. 31, 2013	(31,536)				139		(31,675)	$ 37,709
Balance, Shares at Dec. 31, 2013			1,622,761					37,750,000
Issuance of common stock from exercise of stock options, Amount	40				40
Shares issued during period, Amount		$ 93,970		$ 1		$ 93,969				$ 14,970	$ 37,890
Issuance of common stock from exercise of stock options, Shares			87,475
Shares issued during period, Shares				5,750,000						9,999,999	8,973,905
Vesting of restricted stock, Amount	14				14
Vesting of restricted stock, Shares			138,108
Accretion of redeemable convertible preferred stock to redemption value	(2,294)				(935)		(1,359)	$ 2,294
Issuance of common stock in payment of licensing and consultant fees, Amount	127				127
Issuance of common stock in payment of licensing and consultant fees, Shares			15,872
Stock-based compensation expense	2,512				2,512
Conversion of redeemable convertible preferred stock to common stock, Amount	92,863		$ 2		92,861			$ (92,863)
Conversion of redeemable convertible preferred stock to common stock, Shares			18,007,575					(56,723,904)
Net loss	(33,811)						(33,811)
Balance at Dec. 31, 2014	121,885		$ 3		188,727		(66,845)
Balance, Shares at Dec. 31, 2014			25,621,791
Issuance of common stock from exercise of stock options, Amount	603				603
Shares issued during period, Amount		$ 129,171				$ 129,171
Issuance of common stock from exercise of stock options, Shares			417,475
Shares issued during period, Shares				2,628,571
Vesting of restricted stock, Amount	17				17
Vesting of restricted stock, Shares			128,051
Issuance of common stock under employee stock purchase plan	127				127
Issuance of common stock under employee stock purchase plan, Shares			3,852
Issuance of common stock in payment of licensing and consultant fees, Amount	1,211				1,211
Issuance of common stock in payment of licensing and consultant fees, Shares			23,809
Stock-based compensation expense	15,176				15,176
Net loss	(94,495)						(94,495)
Balance at Dec. 31, 2015	$ 173,695		$ 3		$ 335,032		$ (161,340)
Balance, Shares at Dec. 31, 2015			28,823,549

Consolidated Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Series A Preferred Stock [Member]
Preferred Stock, issuance costs		$ 18
Series B Preferred Stock [Member]
Preferred Stock, issuance costs	$ 30
Series C Preferred Stock [Member]
Preferred Stock, issuance costs	$ 110

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net loss	$ (94,495)	$ (33,811)	$ (18,281)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	15,240	2,512	61
Non-cash licensing and consulting fees	1,211	127	64
Depreciation	115	51	47
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(681)	(715)	(317)
Deferred offering costs	(165)
Accounts payable	2,690	441	674
Accrued expenses and other liabilities	5,404	4,353	236
Net cash used in operating activities	(70,681)	(27,042)	(17,516)
Cash flows from investing activities
Purchase of property and equipment	(198)	(128)	(3)
Net cash used in investing activities	(198)	(128)	(3)
Cash flows from financing activities
Proceeds from stock option exercise and employee stock purchase plan issuances	730	40	51
Proceeds from public offering of common stock, net of commissions and underwriting discounts	129,720	96,255
Payment of offering costs	(584)	(2,285)
Net cash provided by financing activities	129,866	146,870	22,783
Net increase in cash and cash equivalents	58,987	119,700	5,264
Cash and cash equivalents at beginning of period	127,766	8,066	2,802
Cash and cash equivalents at end of period	186,753	127,766	8,066
Supplemental disclosure of non-cash investing and financing activities
Accretion of redeemable convertible preferred stock to redemption value		2,294	7
Conversion of preferred stock to common stock		92,863
Public offering costs included in accounts payable or accrued expenses	$ 165
Series A Preferred Stock [Member]
Cash flows from financing activities
Proceeds from the issuance of preferred stock, net of issuance costs			$ 22,732
Series B Preferred Stock [Member]
Cash flows from financing activities
Proceeds from the issuance of preferred stock, net of issuance costs		14,970
Series C Preferred Stock [Member]
Cash flows from financing activities
Proceeds from the issuance of preferred stock, net of issuance costs		$ 37,890

Nature of the Business

12 Months Ended

Dec. 31, 2015

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 clinical-stage biopharmaceutical company committed to developing and commercializing novel medicines to treat life-altering central nervous system (“CNS”) disorders, where there are inadequate or no approved existing therapies. The Company is targeting CNS indications where patient populations are easily identified, clinical endpoints are well-defined, and development pathways are feasible.

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. under its Second Amended and Restated Certificate of Incorporation.

The Company is subject to risks and uncertainties common to companies in the biotech industry, 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 commercializing pharmaceutical products, if we are able to obtain regulatory approval; the potential for development by third parties of new technological innovations that may compete with the Company’s products; the dependence on key personnel; the challenges of protecting proprietary technology; the need to comply with government regulations; the high costs of drug development; and the uncertainty of being able to secure additional capital when needed to fund operations.

The Company has incurred losses and negative cash flows from operations since its inception. As of December 31, 2015, the Company had an accumulated deficit of $161.3 million. From its inception through December 31, 2015, the Company has raised aggregate net proceeds of $90.6 million from the issuance of Series A, Series B and Series C redeemable convertible preferred stock. In July 2014, the Company raised net proceeds of $94.0 million from the sale of common stock in its initial public offering, (“IPO”). In April 2015, the Company raised net proceeds of $129.1 million from the sale of common stock in a follow-on underwritten public offering. In January 2016, the Company raised net proceeds of $140.4 million from the sale of common stock in a follow-on underwritten public offering. Based on its current operating plans, the Company believes its cash and cash equivalents balance of $186.8 million as of December 31, 2015, in addition to the funds raised from the public offering of common stock in January 2016, will be sufficient to fund its anticipated level of operations into the beginning of 2018.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2015

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 financial statements.

Basis of Presentation

The accompanying consolidated financial statements include those of the Company and its subsidiaries after elimination of all intercompany accounts and transactions. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).

Use of Estimates

The preparation of 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 consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.

Cash and Cash Equivalents

The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents.

Restricted Cash

A deposit of $39 thousand was restricted from withdrawal as of December 31, 2015 and 2014. The restriction is related to securing the Company’s facility lease and expires in 2022 in accordance with the operating lease agreement. This balance is included in restricted cash on the accompanying balance sheets.

Property and Equipment

Property and equipment are recorded at cost and depreciated over their estimated useful lives using the straight-line method. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is credited or charged to income. Repairs and maintenance costs are expensed as incurred.

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets.

Research and Development

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.

Research Contract Costs and Accruals

The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the United States. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Patent Costs

The Company expenses patent costs as incurred and classifies such costs as general and administrative expenses in the accompanying statements of operations and comprehensive loss.

Stock-Based Compensation

The Company recognizes compensation expense for all stock-based awards made to employees and nonemployee directors, including grants of stock options and restricted stock, based on estimated fair value on date of grant, over the requisite service period.

For stock options and restricted stock issued to nonemployee consultants, the Company recognizes the fair value of such instruments as an expense over the period in which the related services are received. The fair value of the awards and measurement of related stock-based compensation is subject to periodic adjustments as the underlying equity instruments vest. For awards that vest upon achievement of a performance condition, the Company recognizes compensation expense when achievement of the performance condition is deemed probable over the implicit service period.

The fair value of each option grant is estimated using the Black-Scholes option-pricing model. Through July 2014, the Company was a private company and lacks sufficient Company-specific historical and implied volatility information. Therefore, the Company estimates expected volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its traded stock price. The expected term of the Company’s options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options, while the expected term of its options granted to consultants and nonemployees has been determined based on the contractual term of the options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

The Company also applies a forfeiture rate in order to calculate stock-based compensation expense. To the extent actual forfeitures differ from the estimates, the difference will be recorded as a cumulative adjustment in the period the estimates are revised. The Company recognizes compensation expense for only the portion of awards that are expected to vest. Expected forfeitures are based on the Company’s historical experience and management’s expectations of future forfeitures.

Basic and Diluted Net Loss Per Share

Upon the closing of the Company’s IPO in July 2014, all of the Company’s outstanding shares of redeemable convertible preferred stock were converted into shares of common stock. Prior to this conversion, the Company followed the two-class method when computing net loss per share as the Company had issued shares that meet the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company’s redeemable convertible preferred shares contractually entitled the holders of such shares to participate in dividends, but did not contractually require the holders of such shares to participate in losses of the Company. Accordingly, the two-class method did not apply for periods in which the Company reported a net loss or a net loss attributable to common stockholders resulting from dividends or accretion related to its redeemable convertible preferred shares.

Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common shares, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is antidilutive.

The Company reported a net loss attributable to common stockholders for the years ended December 31, 2015, 2014 and 2013.

Risks and Uncertainties

The product candidates developed by the Company require approvals from the U.S. Food and Drug Administration or foreign regulatory agencies prior to commercial sales. There can be no assurance that the Company’s current and future product candidates will receive the necessary approvals. If the Company fails to successfully complete clinical development and generate results sufficient to file for regulatory approval or is denied approval or approval is delayed, it may have a material adverse impact on the Company’s business and its financial statements.

The Company is subject to risks common to companies in the development stage including, but not limited to, dependency on the clinical success of its product candidates, ability to obtain regulatory approval of its product candidates, the commercial success of its product, if approved, the need for substantial additional financing to achieve its goals, uncertainty of broad adoption of its approved products, if any, by physicians and consumers, significant competition and untested manufacturing capabilities.

Concentration of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company has all cash and cash equivalents balances at two accredited financial institutions, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.

Income Taxes

The Company accounts for income taxes under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted rates in effect for the year in which these temporary differences are expected to be recovered or settled. Valuation allowances are provided if based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. During November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes, which simplifies the presentation of deferred income taxes. The Company early adopted ASU 2015-17 effective December 31, 2015 on a prospective basis.

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 to be classified and disclosed in one of the following three categories:


Level 1	—	Quoted market prices in active markets for identical assets or liabilities. At December 31, 2015 and 2014, the Company’s Level 1 assets consisted of money market funds totaling $186.8 million and $127.8 million, respectively.

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. At December 31, 2015 and 2014, the Company had no Level 2 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. At December 31, 2015 and 2014, the Company had no Level 3 assets or liabilities.

The Company’s financial instruments generally consist of cash equivalents, accounts payable and accrued expenses. The carrying amounts for the applicable financial instruments reported in the balance sheets approximate their fair values at December 31, 2015 and 2014, respectively.

Deferred Offering Costs

The Company capitalizes certain legal, accounting and other third-party fees that are directly associated with in-process equity financings as other assets until such financings are consummated. After consummation of the IPO in July 2014, $2.3 million of these costs were recorded in stockholders’ equity as a reduction of additional paid-in capital generated as a result of the IPO. After consummation of the follow-on public offering of common stock in April 2015, $0.5 million of these costs were recorded in stockholders’ equity as a reduction of additional paid-in capital generated as a result of the offering. As of December 31, 2015, the Company had recorded deferred offering costs of $0.2 million which are shown as a non-current asset. They are for the follow-on public offering that was consummated in January 2016.

Segment Data

The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on advancing medicines to treat central nervous system disorders, where there are inadequate or no approved existing therapies. All tangible assets are held within the United States.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2015, 2014 and 2013, there was no difference between net loss and comprehensive loss.

Public Offerings

On July 23, 2014, the Company completed the sale of 5,750,000 shares of its common stock in its IPO (the “IPO”), at a price to the public of $18.00 per share, resulting in net proceeds to the Company of $94.0 million after deducting underwriting discounts and commissions and offering costs paid by the Company. The shares began trading on Nasdaq Global Market on July 18, 2014.

In connection with preparing for the IPO, the Company’s board of directors and stockholders approved a 1-for-3.15 reverse stock split of the Company’s common stock effective July 2, 2014. All share and per share amounts in the financial statements contained herein and notes thereto have been retroactively adjusted, where necessary, to give effect to this reverse stock split. In connection with the closing of the IPO, all of the Company’s outstanding redeemable convertible preferred stock automatically converted into shares of common stock as of July 23, 2014, resulting in the issuance by the Company of an additional 18,007,575 shares of common stock. The significant increase in common stock outstanding in July 2014 will impact the year-over-year comparability of the Company’s net loss per share calculations over the next year.

On April 20, 2015, the Company completed the sale of 2,628,571 shares of common stock in an underwritten public offering of its common stock at a price to the public of $52.50 per share, resulting in net proceeds to the Company of $129.1 million after deducting underwriting discounts and commissions and offering costs paid by the Company. A description of the sale of shares of common stock held in January 2016 is included in Note 13.

Recently Issued Accounting Pronouncements

In May 2014, the FASB issued guidance that outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry specific guidance. The guidance is based on the principle that an entity should recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The guidance also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to fulfill a contract. Entities have the option of using either a full retrospective or a modified retrospective approach for the adoption of the new standard. The guidance becomes effective for the Company in the year ending December 31, 2018, and the Company could early adopt the standard for the year ending December 31, 2017. The Company is currently assessing the method of adoption and the impact that this new accounting guidance will have on its consolidated financial statements and footnote disclosures.

In August 2014, the FASB issued ASU 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40). The new guidance addresses management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures. Management’s evaluation should be based on relevant conditions and events that are known and reasonably knowable at the date that the financial statements are issued. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2016. Early adoption is permitted. The Company is evaluating the effect that this guidance will have on its consolidated financial statements.

In November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes, which simplifies the classification of deferred tax assets and liabilities. The new standard requires that all deferred tax assets and liabilities, along with any related valuation allowance, be classified as noncurrent on the balance sheet. The standard is effective for interim and annual periods beginning after December 15, 2016 and allows for early adoption using a full retrospective method or a prospective method. The Company has elected to early adopt the provisions of this new standard using a prospective method. As a result, all deferred taxes as of December 31, 2015 are classified as noncurrent on a net basis in the Company’s consolidated balance sheet, while prior periods remain as previously reported.

In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02—Leases (ASC 842), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e. lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases today. ASC 842 supersedes the previous leases standard, ASC 840 Leases. The standard is effective on January 1, 2019, with early adoption permitted. The Company is in the process of evaluating the impact of this new guidance.

Balance Sheet Components

12 Months Ended

Dec. 31, 2015

Text Block [Abstract]

Balance Sheet Components

3.	Balance Sheet Components

Property and Equipment, net

Property and equipment, net consists of the following:


	Useful Life (Years)		December 31,
	Useful Life (Years)		2015			2014
			(in thousands)
Computer hardware and software		3	$	400		$	206
Furniture and equipment		5		147			103

				547			309
Less: Accumulated depreciation				(261	)		(146	)

Property and equipment, net			$	286		$	163

Depreciation expense for the years ended December 31, 2015, 2014 and 2013 was $0.1 million, $0.1 million and $47 thousand, respectively.

Accrued Expenses

Accrued expenses consist of the following:


	December 31,
	2015		2014
	(in thousands)
Development costs	$	6,466	$	2,788
Employee related expenses		2,718		1,279
Professional services		935		574
Other accrued expenses		29		46

	$	10,148	$	4,687

Commitments and Contingencies

12 Months Ended

Dec. 31, 2015

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

4.	Commitments and Contingencies

Operating Leases

The Company rents its 22,067 square foot office space under an operating lease that was expires in 2022. In March 2013, the Company signed a sublease agreement to sublet 1,900 square feet. Rental income from this sublease was $4 thousand per month. In September, 2015, this sublease was terminated.

Rent expense, net of sublease income, for the years ended December 31, 2015, 2014, and 2013, was $0.4 million, $0.3 million, and $0.3 million, respectively.

Future minimum lease payments under non-cancelable operating leases are as follows at December 31, 2015:


Years Ending December 31,	(in thousands)
2016	$	978
2017		1,088
2018		1,132
2019		1,154
2020		1,176
Thereafter		1,398

	$	6,926

License Agreements

CyDex License Agreement

In September 2015, the Company and CyDex Pharmaceuticals, Inc. (“CyDex”) 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 the Company’s compounds known as SAGE-547 and 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.

As consideration for the inclusion of SAGE-689 in the license granted by CyDex, the Company paid to CyDex $0.1 million, which was recorded as research and development expense in 2015 in connection with execution of the amended and restated license agreement.

The Company is obligated to make milestone payments under the amended and restated license agreement with CyDex based on the achievement of clinical development and regulatory milestones in the amount of $0.8 million in clinical milestones and $3.8 million in regulatory milestones for each of the first two fields with respect to SAGE-547; $1.3 million in clinical milestones and $8.5 million in regulatory milestones for each of the third and fourth fields with respect to SAGE-547; and $0.8 million in clinical milestones and $1.8 million in regulatory milestones for one field with respect to SAGE-689.

For the year ended December 31, 2015, the Company recorded research and development expense and made payments of cash of $0.8 million related to clinical development milestones that were met for this agreement. For the years ended December 31, 2014 and 2013, the Company did not record any expense or make any milestone or royalty payments.

Washington University License Agreement

In November 2013, the Company entered into a license agreement with Washington University whereby the Company was granted exclusive, worldwide rights to develop and commercialize a novel set of neuroactive steroids developed by Washington University. In exchange for development and commercialization rights, the Company paid an upfront, non-refundable payment of $50 thousand and is required to pay an annual license maintenance fee of $15 thousand on each subsequent anniversary date, until the first Phase 2 clinical trial for a licensed product is initiated. 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 totaling $0.1 million was recorded as research and development expense in 2013.

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 year ended December 31, 2014, the Company did not record any expense or make any milestone or royalty payments. In September 2015, a regulatory milestone was met for one of the programs. Accordingly, the Company recorded research and development expenses and made a cash payment of $50 thousand in 2015.

University of California License Agreement

In October 2013, the Company entered into a non-exclusive license agreement with The Regents of the University of California whereby the Company was granted a non-exclusive license to certain clinical data and clinical material for use in the development and commercialization of biopharmaceutical products in the licensed field, including status epilepticus and post-partum 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 will be required to pay to The Regents of the University of California clinical development milestones of up to $0.1 million and pay royalties of less than 1% on net sales for a period of fifteen years following the sale of the first commercial product.

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.

For the years ended December 31, 2014 and 2013, the Company did not record any expense or make any milestone or royalty payments.

During 2015, three clinical development milestones were met. Accordingly, the Company recorded research and development expenses and made cash payments totaling $0.1 million. In June 2015, the Company entered into an exclusive license agreement with The Regents of the University of California 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 thousand and will make annual maintenance fees of $15 thousand 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. Following the first sale, if any, of a licensed product, the Company is obligated to pay royalties at a low single digit percentage of net sales, if any, of licensed products, 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.

Consulting Agreement

In January 2014, the Company entered into a consulting agreement with a nonemployee advisor whereby the Company is obligated to make cash payments of up to $2.0 million and to issue up to 126,984 shares of common stock upon attainment of certain clinical development and regulatory milestones.

In January and March 2014, the first clinical development milestones for each of two programs included in the consulting agreement were met. Accordingly, the Company recorded research and development expense for the year ended December 31, 2014 of $0.2 million, comprised of $50 thousand in cash and $0.1 million related to the issuance of 15,872 shares of the Company’s common stock.

During the year ended December 31, 2015, the second and third clinical development milestones for one of the programs included in the consulting agreement was met. Accordingly, the Company recorded research and development expense for the year ended December 31, 2015 of $1.7 million, comprised of $0.5 million in cash and $1.2 million related to the issuance of 23,809 shares of the Company’s common stock, related to the achievement of these milestones.

Redeemable Convertible Preferred Stock

12 Months Ended

Dec. 31, 2015

Redeemable Convertible Preferred Stock [Member]

Redeemable Convertible Preferred Stock

5.	Redeemable Convertible Preferred Stock

The Company has newly authorized preferred stock amounting to 5,000,000 shares as of December 31, 2015 and 2014. The newly authorized preferred stock was classified under stockholders’ equity (deficit) as of December 31, 2015 and 2014.

As of December 31, 2014 and 2013, the Company’s Certificate of Incorporation, as amended and restated, authorized the Company to issue no shares and 37,750,000, respectively, shares of $0.0001 par value preferred stock. In July 2014, all issued and outstanding redeemable convertible preferred stock was converted to common stock, see Note 2.

The Company had issued Series A, Series B and Series C redeemable convertible preferred stock (collectively, the “Redeemable Preferred Stock”). The Redeemable Preferred Stock was classified outside of stockholders’ equity (deficit) as of December 31, 2013 because the shares contained redemption features that are not solely within the control of the Company.

On March 18, 2013, the Company issued an additional 5,000,000 shares in the second funding of the second tranche of Series A Preferred Stock at $1.00 per share, resulting in net proceeds of $5.0 million.

On July 1, 2013, the Company issued an additional 5,000,000 shares in the third funding of the second tranche of Series A Preferred Stock at $1.00 per share, resulting in net proceeds of $5.0 million.

On September 12, 2013, the Company issued an additional 12,500,000 shares in the third tranche of Series A Preferred Stock at $1.00 per share, resulting in net proceeds of $12.5 million.

On October 18, 2013, the Company issued 250,000 shares of Series A Preferred Stock at $1.00 per share, resulting in net proceeds of $0.3 million.

On October 15, 2013, the Company entered into a Stock Purchase Agreement whereby the Company would issue up to $20.0 million of Series B redeemable convertible preferred stock (“Series B Preferred Stock”) at $1.50 per share. The initial purchase and sale in the amount of $10.0 million could have occurred once certain development milestones had been successfully achieved. The second tranche of $10.0 million could be issued after the initial closing and at the discretion of the Board of Directors. In November 2013, the Company met the development milestones to issue the first tranche of the Series B Preferred Stock.

On January 7, 2014, the Company issued 6,666,666 shares of Series B Preferred Stock at $1.50 per share, resulting in net proceeds of $10.0 million.

On February 12, 2014, the Company issued 3,333,333 shares of Series B Preferred Stock at $1.50 in a second closing, resulting in net proceeds of $5.0 million. At that time, the Company decided not to draw on the remaining $5.0 million of the second tranche of the Series B Preferred Stock.

The Company incurred issuance costs of $30 thousand in 2014 with the issuance of the Series B Preferred Stock which were recorded as a reduction of the proceeds received.

On March 11, 2014, the Company entered into a Stock Purchase Agreement whereby the Company issued 8,973,905 shares of Series C redeemable convertible preferred stock (“Series C Preferred Stock”) at $4.2345 per share for net proceeds of $38.0 million.

The Company incurred issuance costs of $0.1 million in 2014 with the issuance of the Series C Preferred Stock which were recorded as a reduction of the proceeds received.

Common Stock

12 Months Ended

Dec. 31, 2015

Text Block [Abstract]

Common Stock

6.	Common Stock

As of December 31, 2015 and 2014, the Company has authorized 120,000,000 shares of common stock with a par value of $0.0001 per share.

Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends, as may be declared by the Board of Directors, if any. As of December 31, 2015 and 2014, no dividends have been declared.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation

7.	Stock-Based Compensation

2014 Stock Option Plan

On July 2, 2014, the Company’s stockholders approved the 2014 Stock Option and Incentive Plan (the “2014 Stock Option Plan”), which became effective upon the completion of the IPO. The 2014 Stock Option Plan provides for the grant of restricted stock awards, incentive stock options and non-statutory stock options. The 2014 Stock Option Plan replaced the Company’s 2011 Stock Option and Grant Plan (the “2011 Stock Option Plan”). The Company will no longer grant stock options or other awards under the 2011 Stock Option Plan. Any options or awards outstanding under the 2011 Stock Option Plan remained outstanding and effective. As of December 31, 2015, the total number of shares reserved under all equity plans is 3,862,172, and the Company had 859,363 shares available for future issuance under such plans.

The 2014 Stock Option 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 issued and outstanding shares of common stock on the immediately preceding December 31.

Terms of restricted stock awards and stock option agreements, including vesting requirements, are determined by the Board of Directors or the Compensation Committee of the Board of Directors, subject to the provisions of the applicable stock option plan. Options and restricted stock awards granted by the Company generally vest based on the grantee’s continued service with the Company during a specified period following grant. Awards granted to employees generally vest ratably over four years, with a 25% cliff vesting at the one year anniversary for new employee awards. During 2013, the Company also granted a pool of option awards which vest ratably over one year. All awards are exercisable from the date of grant for a period of ten years.

During 2015, the Company granted 497,100 options to employees to purchase shares of common stock that contain performance-based vesting criteria, primarily related to achievement of certain clinical and regulatory development milestones related to the Company’s product candidates. Recognition of stock-based compensation expense associated with these performance-based stock options commences when the performance condition is considered probable of achievement, using management’s best estimates. During the quarter ended June 30, 2015, the achievement of one milestone was considered probable and that milestone was achieved during the quarter ended September 30, 2015. The related expense was recognized over the estimated service period. This milestone represents 35% of the performance-based grants that were made during 2015. The achievement of the remaining milestones was deemed to be not probable as of December 31, 2015 and therefore no expense has been recognized related to these awards. During the year ended December 31, 2015, the Company recognized stock-based compensation expense of $4.8 million related to stock options with performance-based vesting criteria.

Stock-based compensation expense recognized during the years ended December 31, 2015, 2014, and 2013 was as follows:


	Year Ended December 31,
	2015		2014		2013
	(in thousands)
Stock-based compensation expense:
Research and development	$	5,924	$	1,093	$	38
General and administrative		9,316		1,419		23

	$	15,240	$	2,512	$	61

For stock option awards, the fair value of the options is estimated at the grant date using the Black-Scholes option-pricing model, taking into account the terms and conditions upon which options are granted. The fair value of the options is amortized on a straight-line basis for awards to employees and on a graded basis for awards to non-employees over the requisite service period of the awards for awards to employees and graded vesting is used for non-employees. The weighted average grant date fair value per share relating to outstanding stock options granted under the Company’s stock option plans during the years ended December 31, 2015, 2014 and 2013 was $34.08, $14.33 and $0.38, respectively.

The fair value of each option granted to employees and nonemployee directors during the years ended December 31, 2015, 2014 and 2013 under the Company’s stock option plans has been calculated on the date of grant using the following weighted average assumptions:


	Year Ended December 31,
	2015			2014			2013
Expected dividend yield		0.00	%		0.00	%		0.00	%
Expected volatility		90.54	%		98.86	%		99.89	%
Risk free interest rate		1.59	%		1.95	%		1.66	%
Expected term		6.03 years			6.38 years			6.04 years

Expected dividend yield: The Company has not paid and does not anticipate paying any dividends in the foreseeable future.

Risk-free interest rate: The Company determined the risk-free interest rate by using a weighted average equivalent to the expected term based on the U.S. Treasury yield curve in effect as of the date of grant.

Expected volatility: As the Company has only been a public company since July 2014, there is not sufficient historical volatility for the expected term of the options. Therefore, the Company used an average historical share price volatility based on an analysis of reported data for a peer group of comparable companies.

Expected term (in years): Expected term represents the period that the Company’s stock option grants are expected to be outstanding. As the Company has only been a public company since July 2014, there is not sufficient historical term data to calculate the expected term of the options. Therefore, the Company elected to utilize the “simplified” method to estimate the expected term of option grants issued to employees. Under this approach, the weighted average expected life is presumed to be the average of the vesting term and the contractual term of the option.

Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from estimates. The Company estimates forfeitures based on historical termination behavior. For the years ended December 31, 2015, 2014, and 2013, a forfeiture rate of 10% was applied.

For options granted to nonemployees, the expected life of the option used is ten years, which is the contractual term of each such option. All other assumptions used to calculate the grant date fair value are generally consistent with the assumptions used for options granted to employees.

The table below summarizes activity related to stock options:


	Shares			Weighted Average Exercise Price		Weighted Average Remaining Life (in years)		Aggregate Intrinsic Value
								(in thousands)
Outstanding as of December 31, 2014		1,996,615		$	7.01		8.98	$	59,362
Granted		1,516,307			45.64
Exercised		(417,475	)		1.44
Forfeited		(92,638	)		26.93

Outstanding as of December 31, 2015		3,002,809		$	26.67		8.67	$	96,479

Vested or expected to vest as of December 31, 2015		2,421,859		$	24.89		8.60	$	82,344

Exercisable as of December 31, 2015		723,895		$	14.47		8.27	$	31,729

As of December 31, 2015, the Company had unrecognized stock-based compensation expense related to its unvested service-based stock option awards of $31.5 million, which is expected to be recognized over the remaining weighted average vesting period of 3.01 years. The total fair value of shares vested for the years ended December 31, 2015, 2014 and 2013 was $9.2 million, $1.0 million, and $9 thousand, respectively. In addition, the Company has 358,976 shares of outstanding unvested stock options that vest upon the achievement of certain performance criteria. Total unrecognized compensation related to those awards was $7.8 million at December 31, 2015.

The intrinsic value of stock options exercised during the years ended December 31, 2015 and 2014 was $28.4 million and $2.4 million, respectively, and the intrinsic value of stock options exercised during the year ended December 31, 2013 was zero.

Restricted Stock Awards

During the year ended December 31, 2013, the Company granted restricted stock awards to certain officers, employees, directors, and consultants of the Company. During the years ended December 31, 2015, 2014 and 2013, the Company recorded $0.3 million, $0.2 million and $11 thousand, respectively, of stock-based compensation expense related to its restricted stock. The table below summarizes activity relating to restricted stock:


	Shares
Outstanding as of December 31, 2014		170,832
Issued		—
Vested		(128,051	)
Forfeited		—
Repurchased		—

Outstanding as of December 31, 2015		42,781

As of December 31, 2015, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock awards of $34 thousand, which is expected to be recognized over the remaining weighted average vesting period of 0.56 years.

During the years ended December 31, 2015 and 2014, no shares of restricted stock were issued. During the year ended December 31, 2013, current and former employees of the Company purchased a total of 130,158 shares of restricted stock, resulting in proceeds of $50 thousand.

Unvested shares are subject to repurchase by the Company, at the issuance price, upon the employee’s termination at the Company’s sole discretion. In the year ended December 31, 2014, the Company repurchased 6,778 shares of restricted common stock issued to employees at their $0.04 original purchase price per share.

2014 Employee Stock Purchase Plan

On July 2, 2014, the Company’s stockholders approved the 2014 Employee Stock Purchase Plan. A total of 282,000 shares of common stock were initially authorized for issuance under this plan. The 2014 Employee Stock Purchase Plan became effective upon the completion of the IPO. As of December 31, 2015, 3,852 shares have been issued under this plan. Included in accrued liabilities at December 31, 2015 is $64 thousand of stock compensation expense related to an enrollment period for which the related shares had not been issued as of December 31, 2015.

Net Loss Per Share

12 Months Ended

Dec. 31, 2015

Earnings Per Share [Abstract]

Net Loss Per Share

8.	Net Loss Per Share

Basic and diluted net income (loss) per share attributable to common stockholders was calculated as follows for the years ended December 31, 2015, 2014 and 2013:


	Year Ended December 31,
	2015			2014			2013
Basic net loss per share attributable to common stockholders:
Numerator:
Net loss attributable to common stockholders (in thousands)	$	(94,495	)	$	(36,105	)	$	(18,288	)

Denominator:
Weighted average shares of common stock outstanding—basic		27,778,288			21,574,347			1,492,288
Dilutive effect of shares of common stock equivalents resulting from common stock options and preferred common stock (as converted)		—			—			—

Weighted average common stock outstanding—diluted		27,778,288			21,574,347			1,492,288

Net loss per share attributable to common stockholders—basic and diluted	$	(3.40	)	$	(1.67	)	$	(12.26	)

The following common stock equivalents outstanding as of December 31, 2015 and 2014, were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been anti-dilutive:


	Year Ended December 31,
	2015		2014
Options to purchase common stock		2,643,833		1,621,906
Restricted stock		42,781		170,067
Employee Stock Purchase Plan		3,307		—

		2,689,921		1,791,973

Income Taxes

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Income Taxes

9.	Income Taxes

There is no provision for income taxes because the Company has historically incurred operating losses and maintains a full valuation allowance against its net deferred tax assets. The reported amount of income tax expense for the years differs from the amount that would result from applying domestic federal statutory tax rates to pretax losses primarily because of changes in valuation allowance.

A reconciliation of U.S. statutory rate to the Company’s effective tax rate is as follows:


	Year Ended December 31,
	2015			2014			2013
Tax due at statutory rate		34.0	%		34.0	%		34.0	%
State taxes, net of federal		4.0			4.5			5.2
Permanent items		(0.9	)		(1.0	)		(0.1	)
Foreign rate differential		(3.1	)		—			—
Federal and state credits		9.0			8.5			1.5
Change in valuation allowance		(43.1	)		(46.0	)		(40.5	)
Other		0.1			—			(0.1	)

		0.0	%		0.0	%		0.0	%

Significant components of the Company’s net deferred tax asset at December 31, 2015 and 2014 are as follows:


	December 31,
	2015			2014
	(in thousands)
Net operating losses		44,172			21,907
Capitalized start-up costs		2,335			2,514
Accounting method change		(1,347	)		(2,020	)
Tax credit carryforwards		17,013			4,433
Accrued expenses		1,062			494
Depreciation and amortization		716			332
Stock options		5,097			623
Others		21			20

Total net deferred tax asset before valuation allowance		69,069			28,303
Valuation allowance		(69,069	)		(28,303	)

Net deferred tax asset		—			—

As of December 31, 2015, the Company had federal and state net operating loss carryforwards of $131.5 million and $130.7 million, respectively, which begin to expire in 2031. As of December 31, 2015, the Company had federal and state research and development tax credits carryforwards of $1.6 million and $0.7 million, respectively, which begin to expire in 2031 and 2027, respectively. As of December 31, 2015, the Company had federal orphan drug tax credit carry forwards of $16.4 million, which begin to expire in 2034. At December 31, 2015, the Company has excess equity based compensation tax deductions related to net operating losses for federal and state purposes of $18.9 million and $18.9 million respectively. The Company has excess equity based compensation related to credits for federal and state purposes of $1.3 million and $0.2 million, respectively. These excess tax benefits have not been included in the net deferred tax assets before valuation allowance since these benefits would be credited directly to additional paid in capital if subsequently recognized through a reduction in taxes payable.

As of December 31, 2015, net deferred tax assets increased approximately $40.8 million primarily due to the operating loss and tax credits incurred during the year. This increase in net deferred tax assets was offset by a corresponding increase in the valuation allowance.

Management of the Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which are comprised principally of net operating loss carryforwards and capitalized start-up costs. Under the applicable accounting standards, management has considered the Company’s history of losses and concluded that it is more likely than not that the Company will not recognize the benefits of federal and state deferred tax assets. Accordingly, a full valuation allowance of $69.1 million and $28.3 million has been established at December 31, 2015 and 2014, respectively.

Pursuant to Section 382 of the Internal Revenue Code, certain substantial changes in the Company’s ownership may result in a limitation on the amount of net operating loss carryforwards and tax carryforwards that may be used in future years. Utilization of the net operating loss (“NOL”) and tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership change limitations that have occurred previously or that could occur in the future. These ownership changes may limit the amount of NOL and tax credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. The Company has not completed a study to assess whether an ownership change has occurred, or whether there have been multiple ownership changes since its formation, due to significant complexity and related costs associated with such a study. There could also be additional ownership changes in the future which may result in additional limitations on the utilization of NOL carryforwards and credits. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position.

The Company applies the authoritative guidance on accounting for and disclosure of uncertainty in tax positions, which requires the Company to determine whether a tax position of the Company is more likely than not to be sustained upon examination, including resolution of any related appeals of litigation processes, based on the technical merits of the position. For tax positions meeting the more likely than not threshold, the tax amount recognized in the financial statements is reduced by the largest benefit that has a greater than fifty percent likelihood of being realized upon the ultimate settlement with the relevant taxing authority.

The following is a rollforward of the Company’s unrecognized tax benefits:


	Year Ended December 31,
	2015		2014			2013
	(in thousands)
Unrecognized tax benefits—as of the beginning of the year	$	—	$	2,880		$	1,477
Gross increases—current period tax positions		—		—			1,403
Gross decreases—tax positions of prior periods		—		(2,880	)		—

Unrecognized tax benefits—as of the end of the year	$	—	$	—		$	2,880

During 2014, the Company filed an application for change in accounting method with the IRS to capitalize start-up costs that were historically deducted and included as part of the NOL carryforward through December 31, 2013. As a result, the Company’s unrecognized tax benefits, which historically related to start-up costs, are zero at December 31, 2015.

The Company will recognize interest and penalties related to uncertain tax positions in income tax expense when in a taxable income position. As of December 31, 2015 and 2014, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statement of operations.

The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending tax examinations, and the Company’s tax returns are open under statute from 2012 to the present. The tax attributes prior to 2012 may still be adjusted upon examination. The Company’s policy is to record interest and penalties related to income taxes as part of the tax provision.

During November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes, which simplifies the presentation of deferred income taxes. This ASU requires that deferred tax assets and liabilities be classified as non-current in a statement of financial position. The standard is effective for public companies for fiscal years beginning after December 31, 2016, including interim periods within that reporting period. Early adoption is permitted for any interim and annual financial statements that have not yet been issued. The Company early adopted ASU 2015-17 effective December 31, 2015 on a prospective basis. Adoption of this ASU resulted in a reclassification of the current deferred tax liability to a non-current deferred tax liability, which is netted with the long-term deferred tax asset in its consolidated balance sheet as of December 31, 2015. No prior periods were retrospectively adjusted.

Employee Benefit Plan

12 Months Ended

Dec. 31, 2015

Postemployment Benefits [Abstract]

Employee Benefit Plan

10.

Employee Benefit Plan

The Company maintains a 401(k) profit sharing plan (the “Plan”) for its employees. Each participant in the Plan may elect to contribute a portion of his or her annual compensation to the Plan subject to annual limits established by the Internal Revenue Service. Effective November 1, 2014, the Company instituted an employer match of 50% of eligible contributions up to 6% of employee contributions. For the years ended December 31, 2015 and 2014, the Company contributed $0.2 million and $15 thousand, respectively.

Related Party Transactions

12 Months Ended

Dec. 31, 2015

Related Party Transactions

11.

Related Party Transactions

Since inception, the Company has received consulting and management services from Third Rock Ventures LLC, which through its affiliates, owned 16.4% of the Company’s common stock at December 31, 2015. The Company recorded expenses of $21 thousand, $0.2 million, and $0.6 million for these services for the years ended December 31, 2015, 2014, and 2013, respectively.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References + Details

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

12.

Selected Quarterly Financial Data (Unaudited)

The following table contains quarterly financial information for 2015 and 2014. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period.


	2015
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter			Total
	(in thousands, except per share amounts)
Total operating expenses	$	16,897		$	25,059		$	24,082		$	28,612		$	94,650
Loss from operations		(16,897	)		(25,059	)		(24,082	)		(28,612	)		(94,650	)
Net loss and comprehensive loss		(16,871	)		(25,027	)		(24,035	)		(28,562	)		(94,495	)
Net loss attributable to common stockholders		(16,871	)		(25,027	)		(24,035	)		(28,562	)		(94,495	)
Net loss per share attributable to common stockholders—basic and diluted	$	(0.66	)	$	(0.90	)	$	(0.84	)	$	(0.99	)	$	(3.40	)


	2014
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter			Total
	(in thousands, except per share amounts)
Total operating expenses	$	5,790		$	6,188		$	9,471		$	12,361		$	33,810
Loss from operations		(5,790	)		(6,188	)		(9,471	)		(12,361	)		(33,810	)
Net loss and comprehensive loss		(5,790	)		(6,192	)		(9,468	)		(12,361	)		(33,811	)
Net loss attributable to common stockholders		(6,116	)		(7,769	)		(9,859	)		(12,361	)		(36,105	)
Net loss per share attributable to common stockholders—basic and diluted	$	(3.70	)	$	(4.57	)	$	(0.50	)	$	(0.48	)	$	(1.67	)

Subsequent Event

12 Months Ended

Dec. 31, 2015

Subsequent Events [Abstract]

Subsequent Event

13.

Subsequent Event

On January 12, 2016, the Company completed the sale of 3,157,894 shares of its common stock at a price to the public of $47.50 per share, resulting in net proceeds to the Company of $140.4 million after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Basis of Presentation

Basis of Presentation

Use of Estimates

Use of Estimates

Cash and Cash Equivalents

Cash and Cash Equivalents

The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents.

Restricted Cash

Restricted Cash

Property and Equipment

Property and Equipment

Impairment of Long-Lived Assets

Impairment of Long-Lived Assets

Research and Development

Research and Development

Research Contract Costs and Accruals

Research Contract Costs and Accruals

Patent Costs

Patent Costs

The Company expenses patent costs as incurred and classifies such costs as general and administrative expenses in the accompanying statements of operations and comprehensive loss.

Stock-Based Compensation

Stock-Based Compensation

Basic and Diluted Net Loss Per Share

Basic and Diluted Net Loss Per Share

The Company reported a net loss attributable to common stockholders for the years ended December 31, 2015, 2014 and 2013.

Risks and Uncertainties

Risks and Uncertainties

Concentration of Credit Risk and of Significant Suppliers

Concentration of Credit Risk and of Significant Suppliers

Income Taxes

Income Taxes

Fair Value Measurements

Fair Value Measurements


Level 1	—	Quoted market prices in active markets for identical assets or liabilities. At December 31, 2015 and 2014, the Company’s Level 1 assets consisted of money market funds totaling $186.8 million and $127.8 million, respectively.

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. At December 31, 2015 and 2014, the Company had no Level 2 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. At December 31, 2015 and 2014, the Company had no Level 3 assets or liabilities.

Deferred Offering Costs

Deferred Offering Costs

Segment Data

Segment Data

Comprehensive Loss

Comprehensive Loss

Public Offerings

Public Offerings

Recently Issued Accounting Pronouncements

Recently Issued Accounting Pronouncements

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2015

Text Block [Abstract]

Summary of Property and Equipment, Net

Property and equipment, net consists of the following:


	Useful Life (Years)		December 31,
	Useful Life (Years)		2015			2014
			(in thousands)
Computer hardware and software		3	$	400		$	206
Furniture and equipment		5		147			103

				547			309
Less: Accumulated depreciation				(261	)		(146	)

Property and equipment, net			$	286		$	163

Summary of Accrued Expenses

Accrued expenses consist of the following:


	December 31,
	2015		2014
	(in thousands)
Development costs	$	6,466	$	2,788
Employee related expenses		2,718		1,279
Professional services		935		574
Other accrued expenses		29		46

	$	10,148	$	4,687

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2015

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments, Under Non-Cancelable Operating Leases

Future minimum lease payments under non-cancelable operating leases are as follows at December 31, 2015:


Years Ending December 31,	(in thousands)
2016	$	978
2017		1,088
2018		1,132
2019		1,154
2020		1,176
Thereafter		1,398

	$	6,926

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Recognized Stock-Based Compensation Expense

Stock-based compensation expense recognized during the years ended December 31, 2015, 2014, and 2013 was as follows:


	Year Ended December 31,
	2015		2014		2013
	(in thousands)
Stock-based compensation expense:
Research and development	$	5,924	$	1,093	$	38
General and administrative		9,316		1,419		23

	$	15,240	$	2,512	$	61

Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted

The fair value of each option granted to employees and nonemployee directors during the years ended December 31, 2015, 2014, and 2013 under the Company’s stock option plans has been calculated on the date of grant using the following weighted average assumptions:


	Year Ended December 31,
	2015			2014			2013
Expected dividend yield		0.00	%		0.00	%		0.00	%
Expected volatility		90.54	%		98.86	%		99.89	%
Risk free interest rate		1.59	%		1.95	%		1.66	%
Expected term		6.03 years			6.38 years			6.04 years

Summary of Activity Relating to Stock Options

The table below summarizes activity related to stock options:


	Shares			Weighted Average Exercise Price		Weighted Average Remaining Life (in years)		Aggregate Intrinsic Value
								(in thousands)
Outstanding as of December 31, 2014		1,996,615		$	7.01		8.98	$	59,362
Granted		1,516,307			45.64
Exercised		(417,475	)		1.44
Forfeited		(92,638	)		26.93

Outstanding as of December 31, 2015		3,002,809		$	26.67		8.67	$	96,479

Vested or expected to vest as of December 31, 2015		2,421,859		$	24.89		8.60	$	82,344

Exercisable as of December 31, 2015		723,895		$	14.47		8.27	$	31,729

Summary of Activity Relating to Restricted Stock

The table below summarizes activity relating to restricted stock:


	Shares
Outstanding as of December 31, 2014		170,832
Issued		—
Vested		(128,051	)
Forfeited		—
Repurchased		—

Outstanding as of December 31, 2015		42,781

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2015

Earnings Per Share [Abstract]

Summary of Basic and Diluted Net Income (Loss) Per Share Attributable to Common Stockholders

Basic and diluted net income (loss) per share attributable to common stockholders was calculated as follows for the years ended December 31, 2015, 2014 and 2013:


	Year Ended December 31,
	2015			2014			2013
Basic net loss per share attributable to common stockholders:
Numerator:
Net loss attributable to common stockholders (in thousands)	$	(94,495	)	$	(36,105	)	$	(18,288	)

Denominator:
Weighted average shares of common stock outstanding—basic		27,778,288			21,574,347			1,492,288
Dilutive effect of shares of common stock equivalents resulting from common stock options and preferred common stock (as converted)		—			—			—

Weighted average common stock outstanding—diluted		27,778,288			21,574,347			1,492,288

Net loss per share attributable to common stockholders—basic and diluted	$	(3.40	)	$	(1.67	)	$	(12.26	)

Summary of Common Stock Equivalents Outstanding


	Year Ended December 31,
	2015		2014
Options to purchase common stock		2,643,833		1,621,906
Restricted stock		42,781		170,067
Employee Stock Purchase Plan		3,307		—

		2,689,921		1,791,973

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Summary of Reconciliation of U.S. Statutory Rate to Company's Effective Tax Rate

A reconciliation of U.S. statutory rate to the Company’s effective tax rate is as follows:


	Year Ended December 31,
	2015			2014			2013
Tax due at statutory rate		34.0	%		34.0	%		34.0	%
State taxes, net of federal		4.0			4.5			5.2
Permanent items		(0.9	)		(1.0	)		(0.1	)
Foreign rate differential		(3.1	)		—			—
Federal and state credits		9.0			8.5			1.5
Change in valuation allowance		(43.1	)		(46.0	)		(40.5	)
Other		0.1			—			(0.1	)

		0.0	%		0.0	%		0.0	%

Summary of Significant Components of Company's Net Deferred Tax Asset

Significant components of the Company’s net deferred tax asset at December 31, 2015 and 2014 are as follows:


	December 31,
	2015			2014
	(in thousands)
Net operating losses		44,172			21,907
Capitalized start-up costs		2,335			2,514
Accounting method change		(1,347	)		(2,020	)
Tax credit carryforwards		17,013			4,433
Accrued expenses		1,062			494
Depreciation and amortization		716			332
Stock options		5,097			623
Others		21			20

Total net deferred tax asset before valuation allowance		69,069			28,303
Valuation allowance		(69,069	)		(28,303	)

Net deferred tax asset		—			—

Summary of Rollforward of Company's Unrecognized Tax Benefits

The following is a rollforward of the Company’s unrecognized tax benefits:


	Year Ended December 31,
	2015		2014			2013
	(in thousands)
Unrecognized tax benefits—as of the beginning of the year	$	—	$	2,880		$	1,477
Gross increases—current period tax positions		—		—			1,403
Gross decreases—tax positions of prior periods		—		(2,880	)		—

Unrecognized tax benefits—as of the end of the year	$	—	$	—		$	2,880

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Summary of Quarterly Financial Information


	2015
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter			Total
	(in thousands, except per share amounts)
Total operating expenses	$	16,897		$	25,059		$	24,082		$	28,612		$	94,650
Loss from operations		(16,897	)		(25,059	)		(24,082	)		(28,612	)		(94,650	)
Net loss and comprehensive loss		(16,871	)		(25,027	)		(24,035	)		(28,562	)		(94,495	)
Net loss attributable to common stockholders		(16,871	)		(25,027	)		(24,035	)		(28,562	)		(94,495	)
Net loss per share attributable to common stockholders—basic and diluted	$	(0.66	)	$	(0.90	)	$	(0.84	)	$	(0.99	)	$	(3.40	)


	2014
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter			Total
	(in thousands, except per share amounts)
Total operating expenses	$	5,790		$	6,188		$	9,471		$	12,361		$	33,810
Loss from operations		(5,790	)		(6,188	)		(9,471	)		(12,361	)		(33,810	)
Net loss and comprehensive loss		(5,790	)		(6,192	)		(9,468	)		(12,361	)		(33,811	)
Net loss attributable to common stockholders		(6,116	)		(7,769	)		(9,859	)		(12,361	)		(36,105	)
Net loss per share attributable to common stockholders—basic and diluted	$	(3.70	)	$	(4.57	)	$	(0.50	)	$	(0.48	)	$	(1.67	)

Nature of the Business - Additional Information (Detail) - USD ($) $ in Thousands				12 Months Ended
	Jan. 12, 2016	Apr. 20, 2015	Jul. 23, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Nature Of Business [Line Items]
Accumulated deficit				$ (161,340)	$ (66,845)
Net proceeds from sale of common stock			$ 94,000
Cash and cash equivalents				186,753	127,766	$ 8,066	$ 2,802
Proceeds from underwritten initial public offering of common stock, net proceeds		$ 129,100		129,720	$ 96,255
Subsequent Event [Member]
Nature Of Business [Line Items]
Proceeds from underwritten initial public offering of common stock, net proceeds	$ 140,400
Redeemable Convertible Preferred Stock [Member]
Nature Of Business [Line Items]
Convertible preferred stock proceeds raised				$ 90,600

Summary of Significant Accounting Policies - Additional Information (Detail)				1 Months Ended	12 Months Ended
	Apr. 20, 2015 USD ($) $ / shares shares	Jul. 23, 2014 USD ($) $ / shares shares	Jul. 02, 2014	Apr. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Restricted cash deposit					$ 39,000	$ 39,000
Payment of offering costs		$ 2,300,000		$ 500,000	584,000	2,285,000
Deferred offering costs					$ 200,000
Issuance of common stock, shares \| shares	2,628,571
Common stock price per share \| $ / shares	$ 52.50
Proceeds from initial public offering of common stock, net of commissions and underwriting discounts		$ 94,000,000
Reverse stock split description					In connection with preparing for the IPO, the Company's board of directors and stockholders approved a 1-for-3.15 reverse stock split of the Company's common stock
Reverse stock split effective date					Jul. 02, 2014
Reverse stock split ratio			0.3175
Issuance of additional shares of common stock upon conversion \| shares		18,007,575
Proceeds from underwritten initial public offering of common stock, net proceeds	$ 129,100,000				$ 129,720,000	96,255,000
Fair Value, Inputs, Level 1 [Member] \| Money Market Funds [Member]
Summary Of Significant Accounting Policies [Line Items]
Assets fair value					186,800,000	127,800,000
Fair Value, Inputs, Level 2 [Member]
Summary Of Significant Accounting Policies [Line Items]
Assets fair value					0	0
Liabilities fair value					0	0
Fair Value, Inputs, Level 3 [Member]
Summary Of Significant Accounting Policies [Line Items]
Assets fair value					0	0
Liabilities fair value					$ 0	$ 0
Initial Public Offering [Member]
Summary Of Significant Accounting Policies [Line Items]
Issuance of common stock, shares \| shares		5,750,000
Common stock price per share \| $ / shares		$ 18.00
Proceeds from initial public offering of common stock, net of commissions and underwriting discounts		$ 94,000,000

Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 547	$ 309
Less: Accumulated depreciation	(261)	(146)
Property and equipment, net	$ 286	163
Computer Hardware and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Property and equipment, gross	$ 400	206
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Property and equipment, gross	$ 147	$ 103

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 100	$ 100	$ 47

Balance Sheet Components - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Development costs	$ 6,466	$ 2,788
Employee related expenses	2,718	1,279
Professional services	935	574
Other accrued expenses	29	46
Total accrued expenses	$ 10,148	$ 4,687

Commitments and Contingencies - Operating Leases - Additional Information (Detail) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2013 USD ($) ft²	Dec. 31, 2015 USD ($) ft²	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Commitments And Contingencies [Line Items]
Rent expense, net of sublease income \| $		$ 400	$ 300	$ 300
Operating Lease One [Member]
Commitments And Contingencies [Line Items]
Office space rented under operating lease \| ft²		22,067
Operating lease end year		2022
Sublease Agreement [Member]
Commitments And Contingencies [Line Items]
Area of leased property \| ft²	1,900
Lease income per month \| $	$ 4

Commitments and Contingencies - Schedule of Future Minimum Lease Payments, Under Non-Cancelable Operating Leases (Detail) $ in Thousands	Dec. 31, 2015 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2016	$ 978
2017	1,088
2018	1,132
2019	1,154
2020	1,176
Thereafter	1,398
Total Operating leases, future minimum payments	$ 6,926

Commitments and Contingencies - CyDex License Agreement - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments And Contingencies [Line Items]
Research and development expense	$ 69,357,000	$ 24,100,000	$ 14,357,000
CyDex License Agreement [Member]
Commitments And Contingencies [Line Items]
Research and development expense	100,000
CyDex License Agreement [Member] \| First and Second Clinical Development Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	800,000
CyDex License Agreement [Member] \| First and Second Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	3,800,000
CyDex License Agreement [Member] \| Third and Fourth Clinical Development Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	1,300,000
CyDex License Agreement [Member] \| Third and Fourth Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	8,500,000
CyDex License Agreement [Member] \| Clinical Development [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	800,000
Research and development expense related to milestone expense	800,000	0	0
Milestone payments	800,000	$ 0	$ 0
CyDex License Agreement [Member] \| Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 1,800,000

Commitments and Contingencies - Washington University License Agreement - Additional Information (Detail) - Washington University License Agreement [Member] - USD ($)	1 Months Ended	12 Months Ended
	Nov. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments And Contingencies [Line Items]
Upfront non-refundable payment	$ 50,000
Annual license maintenance fee	15,000
Issuance of common stock, shares				47,619
Research and development expense related to milestone expense				$ 100,000
Clinical Development [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	700,000
Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 500,000
Research and development expense related to milestone expense		$ 50,000	$ 0
Milestone payments		$ 50,000	$ 0

Commitments and Contingencies - University of California License Agreements - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Oct. 31, 2013
Commitments And Contingencies [Line Items]
Milestone or royalty payments, expense recognized			$ 0	$ 0
University of California License Agreement [Member]
Commitments And Contingencies [Line Items]
Percentage of net sales		1.00%
Upfront payment	$ 50,000
Annual license maintenance fee	15,000
University of California License Agreement [Member] \| After The Effective Date [Member]
Commitments And Contingencies [Line Items]
Licenses Expiration period, maximum		27 years
University of California License Agreement [Member] \| After The First Sale [Member]
Commitments And Contingencies [Line Items]
Licenses Expiration period, maximum		15 years
University of California License Agreement [Member] \| Clinical Development [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments					$ 100,000
Research and development expense related to milestone expense		$ 100,000
Milestone payments		$ 100,000
University of California License Agreement [Member] \| Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	700,000
University of California License Agreement [Member] \| Sales Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 2,000,000

Commitments and Contingencies - Consulting Agreement - Additional Information (Detail) - Consulting Agreement [Member] - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Clinical Development and Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Milestone payment	$ 2,000,000
Shares of common stock for attaining milestones	126,984
First Clinical Development Milestones [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense			$ 200,000
Milestone payments			50,000
Payments for stock issued upon reaching a milestone			$ 100,000
Milestone based share compensation, shares issued			15,872
Second and Third Clinical Development Milestones [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense		$ 1,700,000
Milestone payments		500,000
Payments for stock issued upon reaching a milestone		$ 1,200,000
Milestone based share compensation, shares issued		23,809

Redeemable Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands								12 Months Ended
	Mar. 11, 2014	Feb. 12, 2014	Jan. 07, 2014	Oct. 18, 2013	Sep. 12, 2013	Jul. 01, 2013	Mar. 18, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Nov. 30, 2013	Oct. 15, 2013
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized								0	37,750,000
Redeemable convertible preferred stock, par value								$ 0.0001	$ 0.0001
Preferred stock, shares authorized								5,000,000		5,000,000
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, par value				$ 1.00
Redeemable convertible preferred stock, shares issued				250,000
Proceeds from the issuance of preferred stock, net proceeds				$ 300
Redeemable convertible preferred Stock, issuance costs									$ 18
Series A Preferred Stock [Member] \| Second Tranche [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, par value						$ 1.00	$ 1.00
Redeemable convertible preferred stock, shares issued						5,000,000	5,000,000
Proceeds from the issuance of preferred stock, net proceeds						$ 5,000	$ 5,000
Series A Preferred Stock [Member] \| Third Tranche [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, par value					$ 1.00
Redeemable convertible preferred stock, shares issued					12,500,000
Proceeds from the issuance of preferred stock, net proceeds					$ 12,500
Series B Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, par value		$ 1.50	$ 1.50									$ 1.50
Redeemable convertible preferred stock, shares issued		3,333,333	6,666,666									20,000,000
Proceeds from the issuance of preferred stock, net proceeds		$ 5,000	$ 10,000
Redeemable convertible preferred stock												$ 10,000
Redeemable convertible preferred Stock, issuance costs								$ 30
Series B Preferred Stock [Member] \| Second Tranche [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, Undrawn amount		$ 5,000
Series B Preferred Stock [Member] \| First Tranche [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock											$ 10,000
Series C Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, par value	$ 4.2345
Redeemable convertible preferred stock, shares issued	8,973,905
Proceeds from the issuance of preferred stock, net proceeds	$ 38,000
Redeemable convertible preferred Stock, issuance costs								$ 110

Common Stock - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Common stock, shares authorized	120,000,000	120,000,000
Common stock, par value	$ 0.0001	$ 0.0001
Dividends declared	$ 0	$ 0
Voting rights	Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company's stockholders.

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Jul. 02, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation granted under plan vest period		4 years		1 year
Share based compensation, vest period		1 year
Share based compensation, term of plan		10 years
Weighted average grant date fair value per share		$ 34.08	$ 14.33	$ 0.38
Share option, forfeiture rate		10.00%	10.00%	10.00%
Total unrecognized stock-based compensation expense		$ 7,800
Stock-based compensation expense		$ 15,240	$ 2,512	$ 61
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option grant		1,516,307
Total unrecognized stock-based compensation expense		$ 31,500
Weighted average period of unrecognized compensation costs		3 years 4 days
Total fair value of shares vested		$ 9,200	1,000	9
Intrinsic value of options exercised		$ 28,400	2,400	0
Number of shares outstanding unvested stock options		358,976
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense		$ 34
Weighted average period of unrecognized compensation costs		6 months 22 days
Stock-based compensation expense		$ 300	$ 200	$ 11
Issued, Shares-Restricted stock		0	0	130,158
Proceeds from restricted shares sold to employees				$ 50
Stock repurchased, shares		0	6,778
Stock repurchased, purchase price per share			$ 0.04
Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting percentage		25.00%
2014 Stock Option Plan and 2011 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares reserved under equity plan		3,862,172
Number of shares available for future issuance under the plan		859,363
2011 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option grant		0
2014 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of performance based grants that were achieved		35.00%
2014 Stock Option Plan [Member] \| Performance Milestone [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options with performance-based criteria		497,100
Stock-based compensation expense		$ 4,800
2014 Stock Option Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of increase to stock option on issued and outstanding shares of Common stock	4.00%
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options with performance-based criteria	282,000
Number of shares issued under the plan		3,852
Accrued liabilities		$ 64

Stock-Based Compensation - Summary of Recognized Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 15,240	$ 2,512	$ 61
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	5,924	1,093	38
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 9,316	$ 1,419	$ 23

Stock-Based Compensation - Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility	90.54%	98.86%	99.89%
Risk free interest rate	1.59%	1.95%	1.66%
Expected term	6 years 11 days	6 years 4 months 17 days	6 years 15 days

Stock-Based Compensation - Summary of Activity Relating to Stock Options (Detail) - Options to Purchase Common Stock [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Stock options	1,996,615
Granted, Stock options	1,516,307
Exercised, Stock options	(417,475)
Forfeited, Stock options	(92,638)
Ending balance, Outstanding Shares-Stock options	3,002,809	1,996,615
Vested or expected to vest, Stock options	2,421,859
Exercisable, Stock options	723,895
Beginning balance, Weighted Average Exercise Price-Stock options	$ 7.01
Granted, Weighted Average Exercise Price-Stock options	45.64
Exercised, Weighted Average Exercise Price-Stock options	1.44
Forfeited, Weighted Average Exercise Price-Stock options	26.93
Ending balance, Outstanding Weighted Average Exercise Price-Stock options	26.67	$ 7.01
Vested or expected to vest, Weighted Average Exercise Price-Stock options	24.89
Exercisable, Weighted Average Exercise Price-Stock options	$ 14.47
Outstanding, Weighted Average Remaining Life-Stock options	8 years 8 months 1 day	8 years 11 months 23 days
Vested or expected to vest, Weighted Average Remaining Life-Stock options	8 years 7 months 6 days
Exercisable, Weighted Average Remaining Life-Stock options	8 years 3 months 7 days
Outstanding, Aggregate Intrinsic Value-Stock options	$ 96,479	$ 59,362
Vested or expected to vest, Aggregate Intrinsic Value-Stock options	82,344
Exercisable, Aggregate Intrinsic Value-Stock options	$ 31,729

Stock-Based Compensation - Summary of Activity Relating to Restricted Stock (Detail) - Restricted Stock [Member] - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, Shares at beginning balance-Restricted stock		170,832
Issued, Shares-Restricted stock	0	0	130,158
Vested, Shares-Restricted stock	(128,051)
Forfeited, Shares-Restricted stock	0
Repurchased, Shares-Restricted stock	0	(6,778)
Outstanding, Shares at ending balance-Restricted stock	42,781		170,832

Net Loss Per Share - Schedule of Basic and Diluted Net Income (Loss) Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net loss attributable to common stockholders	$ (28,562)	$ (24,035)	$ (25,027)	$ (16,871)	$ (12,361)	$ (9,859)	$ (7,769)	$ (6,116)	$ (94,495)	$ (36,105)	$ (18,288)
Denominator:
Weighted average shares of common stock outstanding-basic									27,778,288	21,574,347	1,492,288
Dilutive effect of shares of common stock equivalents resulting from common stock options and preferred common stock (as converted)									0	0	0
Weighted average common stock outstanding-diluted									27,778,288	21,574,347	1,492,288
Net loss per share attributable to common stockholders-basic and diluted	$ (0.99)	$ (0.84)	$ (0.90)	$ (0.66)	$ (0.48)	$ (0.50)	$ (4.57)	$ (3.70)	$ (3.40)	$ (1.67)	$ (12.26)

Net Loss Per Share - Summary of Common Stock Equivalents Outstanding (Detail) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	2,689,921	1,791,973
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	2,643,833	1,621,906
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	42,781	170,067
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	3,307

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Line Items]
Provision for income taxes	$ 0
Federal operating loss carryforwards	131,500,000
State operating loss carryforwards	$ 130,700,000
Federal and state net operating loss carryforwards expiration year	2031
Federal orphan drug tax credit carry forwards	$ 16,400,000
Tax credit carry forwards expiration period	2034
Change in amount of deferred tax assets	$ 40,800,000
Valuation allowance	$ 69,069,000	$ 28,303,000
Income tax position description	For tax positions meeting the more likely than not threshold, the tax amount recognized in the financial statements is reduced by the largest benefit that has a greater than fifty percent likelihood of being realized upon the ultimate settlement with the relevant taxing authority.
Unrecognized tax benefit related to start-up costs	$ 0		$ 2,880,000	$ 1,477,000
Accrued interest or penalties related to uncertain tax positions	0	$ 0
Uncertain tax positions	0
Domestic Tax Authority [Member]
Income Tax Disclosure [Line Items]
Research and development tax credits carryforwards	$ 1,600,000
Research and development tax credits carryforwards expiration year	2031
Excess equity based compensation, tax deductions	$ 18,900,000
Excess equity based compensation, tax credits	1,300,000
State and Local Jurisdiction [Member]
Income Tax Disclosure [Line Items]
Research and development tax credits carryforwards	$ 700,000
Research and development tax credits carryforwards expiration year	2027
Excess equity based compensation, tax deductions	$ 18,900,000
Excess equity based compensation, tax credits	$ 200,000

Income Taxes - Summary of Reconciliation of U.S. Statutory Rate to Company's Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Tax due at statutory rate	34.00%	34.00%	34.00%
State taxes, net of federal	4.00%	4.50%	5.20%
Permanent items	(0.90%)	(1.00%)	(0.10%)
Foreign rate differential	(3.10%)
Federal and state credits	9.00%	8.50%	1.50%
Change in valuation allowance	(43.10%)	(46.00%)	(40.50%)
Other	0.10%		(0.10%)
Total effective tax rate	0.00%	0.00%	0.00%

Income Taxes - Summary of Significant Components of Company's Net Deferred Tax Asset (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Net operating losses	$ 44,172	$ 21,907
Capitalized start-up costs	2,335	2,514
Accounting method change	(1,347)	(2,020)
Tax credit carryforwards	17,013	4,433
Accrued expenses	1,062	494
Depreciation and amortization	716	332
Stock options	5,097	623
Others	21	20
Total net deferred tax asset before valuation allowance	69,069	28,303
Valuation allowance	(69,069)	(28,303)
Net deferred tax asset	$ 0	$ 0

Income Taxes - Summary of Rollforward of Company's Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Unrecognized tax benefits-as of the beginning of the year	$ 2,880	$ 1,477
Gross increases-current period tax positions		1,403
Gross decreases-tax positions of prior periods	$ (2,880)
Unrecognized tax benefits-as of the end of the year		$ 2,880

Employee Benefit Plan - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Nov. 01, 2014	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options Outstanding, Weighted Average Exercise Price, and Additional Disclosures [Abstract]
Employer matching contribution, percent of match	50.00%
Maximum annual contributions per employee, percent	6.00%
Employer contribution		$ 200	$ 15

Related Party Transactions - Additional Information (Detail) - Third Rock Ventures LLC [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Percentage of ownership held with related party transactions	16.40%
Payment for consulting and management services	$ 21	$ 200	$ 600

Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Total operating expenses	$ 28,612	$ 24,082	$ 25,059	$ 16,897	$ 12,361	$ 9,471	$ 6,188	$ 5,790	$ 94,650	$ 33,810	$ 18,279
Loss from operations	(28,612)	(24,082)	(25,059)	(16,897)	(12,361)	(9,471)	(6,188)	(5,790)	(94,650)	(33,810)	(18,279)
Net loss and comprehensive loss	(28,562)	(24,035)	(25,027)	(16,871)	(12,361)	(9,468)	(6,192)	(5,790)	(94,495)	(33,811)	(18,281)
Net loss attributable to common stockholders	$ (28,562)	$ (24,035)	$ (25,027)	$ (16,871)	$ (12,361)	$ (9,859)	$ (7,769)	$ (6,116)	$ (94,495)	$ (36,105)	$ (18,288)
Net loss per share attributable to common stockholders-basic and diluted	$ (0.99)	$ (0.84)	$ (0.90)	$ (0.66)	$ (0.48)	$ (0.50)	$ (4.57)	$ (3.70)	$ (3.40)	$ (1.67)	$ (12.26)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Subsequent Event - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Jan. 12, 2016	Apr. 20, 2015	Dec. 31, 2015	Dec. 31, 2014
Subsequent Event [Line Items]
Issuance of common stock, shares		2,628,571
Common stock price per share		$ 52.50
Proceeds from public offering of common stock, net of commissions and underwriting discounts and estimated offering expenses		$ 129,100	$ 129,720	$ 96,255
Subsequent Event [Member]
Subsequent Event [Line Items]
Issuance of common stock, shares	3,157,894
Common stock price per share	$ 47.50
Proceeds from public offering of common stock, net of commissions and underwriting discounts and estimated offering expenses	$ 140,400