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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2015	Nov. 01, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Trading Symbol	SAGE
Entity Registrant Name	Sage Therapeutics, Inc.
Entity Central Index Key	0001597553
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		28,862,471

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 204,877	$ 127,766
Prepaid expenses and other current assets	2,604	1,056
Total current assets	207,481	128,822
Property and equipment, net	249	163
Restricted cash	39	39
Deferred tax assets	641	641
Total assets	208,410	129,665
Current liabilities:
Accounts payable	3,246	2,429
Accrued expenses	6,404	4,687
Deferred tax liabilities	641	641
Total current liabilities	10,291	7,757
Other liabilities	15	23
Total liabilities	10,306	7,780
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized at September 30, 2015 and December 31, 2014, respectively; no shares issued or outstanding at September 30, 2015 and December 31, 2014, respectively
Common stock, $0.0001 par value; 120,000,000 shares authorized at September 30, 2015 and December 31, 2014, respectively; 28,788,885 and 25,621,791 shares issued and outstanding at September 30, 2015 and December 31, 2014, respectively	3	3
Additional paid-in capital	330,879	188,727
Accumulated deficit	(132,778)	(66,845)
Total stockholders' equity	198,104	121,885
Total liabilities and stockholders' equity	$ 208,410	$ 129,665

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 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	28,788,885	25,621,791
Common stock, shares outstanding	28,788,885	25,621,791

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Operating expenses:
Research and development	$ 17,478	$ 6,601	$ 48,981	$ 15,155
General and administrative	6,604	2,869	17,057	6,294
Total operating expenses	24,082	9,470	66,038	21,449
Loss from operations	(24,082)	(9,470)	(66,038)	(21,449)
Interest income, net	53	3	115	4
Other expense, net	(6)	(1)	(10)	(5)
Net loss and comprehensive loss	(24,035)	(9,468)	(65,933)	(21,450)
Accretion of redeemable convertible preferred stock to redemption value		(391)		(2,294)
Net loss attributable to common stockholders	$ (24,035)	$ (9,859)	$ (65,933)	$ (23,744)
Net loss per share attributable to common stockholders-basic and diluted	$ (0.84)	$ (0.50)	$ (2.40)	$ (3.08)
Weighted average number of common shares used in net loss per share attributable to common stockholders-basic and diluted	28,737,743	19,581,624	27,430,275	7,711,038

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities
Net loss	$ (65,933)	$ (21,450)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	11,154	1,186
Non-cash licensing and consulting fees	1,211	127
Depreciation	83	35
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,548)	(722)
Accounts payable	808	(6)
Accrued expenses and other liabilities	1,661	2,455
Net cash used in operating activities	(52,564)	(18,375)
Cash flows from investing activities
Purchase of property and equipment	(160)	(83)
Net cash used in investing activities	(160)	(83)
Cash flows from financing activities
Proceeds from stock option exercises and employee stock purchase plan issuances	663	39
Payment of offering costs	(548)	(2,035)
Proceeds from public offering of common stock, net of commissions and underwriting discounts	129,720	96,255
Net cash provided by financing activities	129,835	147,119
Net increase in cash and cash equivalents	77,111	128,661
Cash and cash equivalents at beginning of period	127,766	8,066
Cash and cash equivalents at end of period	204,877	136,727
Supplemental disclosure of non-cash financing activities
Accretion of redeemable convertible preferred stock to redemption value		2,294
Public offering costs included in accounts payable or accrued expenses	$ 4	246
Conversion of preferred stock to common stock		92,863
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 Operations	9 Months Ended
Nature of Operations	Sep. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	1. Nature of Operations 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. This focus allows the Company to make highly informed decisions when advancing its product candidates through the development process. 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 nonclinical and clinical development; the challenges associated with gaining regulatory approval of such product candidates; 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 September 30, 2015, the Company had an accumulated deficit of $132.8 million. From its inception through September 30, 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. Based on its current operating plans, the Company believes its cash and cash equivalents balance of $204.9 million as of September 30, 2015 will be sufficient to fund its anticipated level of operations through mid-2017.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2015

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The unaudited interim consolidated financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2014.

The unaudited interim consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements. In the opinion of the Company’s management, the accompanying unaudited interim consolidated financial statements contain all adjustments which are necessary to present fairly the Company’s financial position as of September 30, 2015, the results of its operations and comprehensive loss for the three and nine months ended September 30, 2015 and 2014, and its cash flows for the nine months ended September 30, 2015 and 2014. Such adjustments are of a normal and recurring nature. The results for the three and nine months ended September 30, 2015 are not indicative of the results for the year ending December 31, 2015, or for any future period.

On July 23, 2014, the Company completed the sale of 5,750,000 shares of its common stock in its 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 the 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 unaudited consolidated 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 through the end of 2015.

On April 20, 2015, the Company completed the sale of 2,628,571 shares of common stock in its 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.

Principles of Consolidation

The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries as disclosed in Note 2, Summary of Significant Accounting Policies, within the “Notes to Consolidated Financial Statements” accompanying its Annual Report on Form 10-K for the fiscal year ended December 31, 2014, as amended. Intercompany accounts and transactions have been eliminated.

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 of 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.

Use of Estimates

The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America 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.

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 September 30, 2015 and December 31, 2014, the Company’s Level 1 assets consisted of money market funds totaling $204.9 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 September 30, 2015 and December 31, 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 September 30, 2015 and December 31, 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 September 30, 2015 and December 31, 2014.

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 public offering of common stock in April 2015, $0.6 million of these costs were recorded in stockholders’ equity as a reduction of additional paid-in capital generated as a result of the offering.

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 CNS, where there are inadequate or no approved existing therapies. All tangible assets are held within the United States.

Accrued Expenses

9 Months Ended

Sep. 30, 2015

Text Block [Abstract]

Accrued Expenses

3. Accrued Expenses

Accrued expenses consist of the following (amounts in thousands):


	September 30, 2015		December 31, 2014

Development costs	$	4,096	$	2,788
Employee-related expenses		1,545		1,279
Professional services		756		574
Other accrued expenses		7		46

	$	6,404	$	4,687

Commitments and contingencies	9 Months Ended
Commitments and contingencies	Sep. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	4. Commitments and contingencies *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 a milestone to CyDex of $0.1 million, which was recorded as research and development expense in the three months ended September 30, 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. In March 2015, a clinical development milestone was met for the SAGE-547 program under the license agreement with CyDex, and accordingly, the Company recorded research and development expense for the three months ended March 31, 2015 of $0.3 million. In April 2015, an additional clinical development milestone for the SAGE-547 program was met under the license agreement with CyDex, and accordingly, the Company recorded research and development expense for the three months ended June 30, 2015 of $0.5 million. The Company will also be required to pay royalties to CyDex on sales of SAGE-547 and SAGE-689, if successfully developed, in the low single digits based on levels of net sales. The Company and CyDex are also parties to a supply agreement which was amended in September 2015 to cover the supply of CyDex’s Captisol for use in the manufacture of products incorporating SAGE-689. Under the amended supply agreement with CyDex, the Company is required to purchase all of its requirements for Captisol with respect to SAGE-547 and SAGE-689 from CyDex, and CyDex is required to supply the Company with Captisol for such purposes, subject to certain limitations. *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 $50,000 and is required to pay an annual license maintenance fee of $15,000 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. In September 2015, a regulatory milestone was met for one of the programs. Accordingly, the Company recorded research and development expenses for the three months ended September 30, 2015 of $50,000. *University of California License Agreements* In October 2013, the Company entered into a non-exclusive license agreement with The Regents of the University of California 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. In March 2015, a clinical development milestone was met. Accordingly, the Company recorded research and development expenses for the three months ended March 31, 2015 totaling $0.1 million. In June 2015, an additional clinical development milestone was met. Accordingly, the Company recorded research and development expenses for the three months ended June 30, 2015 totaling $25,000. In September 2015, an additional clinical development milestone was met. Accordingly, the Company recorded research and development expenses for the three months ended September 30, 2015 totaling $25,000. 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 $50,000 and will make annual maintenance fees of $15,000 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 $50,000 in cash and $0.1 million related to the issuance of 15,872 shares of the Company’s common stock. In March 2015, the second clinical development milestone for one of the programs included in the consulting agreement was met. Accordingly, the Company recorded research and development expense for the three months ended March 31, 2015 of $0.6 million, comprised of $0.2 million in cash and $0.4 million related to the issuance of 7,936 shares of the Company’s common stock. In April 2015, the third clinical development milestone for one of the programs included in the consulting agreement was met. Accordingly, the Company recorded research and development expense for the three months ended June 30, 2015 of $1.1 million, comprised of $0.3 million in cash and $0.8 million related to the issuance of 15,873 shares of the Company’s common stock.

Stock-Based Compensation

9 Months Ended

Sep. 30, 2015

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

Stock-Based Compensation

5. 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, non-statutory stock options, among others. The 2014 Stock Option Plan replaced the Company’s 2011 Stock Option and Grant Plan (the “2011 Stock Option Plan”). The Company will grant no further 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 September 30, 2015, the total number of shares reserved under the 2014 Stock Option Plan and the 2011 Stock Option Plan was 3,868,298 and the Company had 997,486 shares available for future issuance under the 2014 Stock Option Plan.

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. On January 1, 2015, 773,779 shares of common stock, representing 3% of the Company’s issued and outstanding shares of common stock as of December 31, 2014, were added to the 2014 Stock Option Plan. Such shares are included in the equity plan totals specified in the paragraph above.

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 September 30, 2015, 3,852 shares of common stock have been issued under this plan. During the nine months ended September 30, 2015, issuances of common stock under the Employee Stock Purchase Plan resulted in proceeds to the Company of $0.1 million.

Stock-Based Compensation

Terms of restricted stock awards and stock option agreements, including vesting requirements, are determined by the Compensation Committee of the Company’s Board of Directors or 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 continued service of the grantee with the Company during a specified period following the grant. Awards generally vest ratably over four years, with a 25% cliff vesting at the one year anniversary.

During the nine months ended September 30, 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 the nine months ended September 30, 2015. The achievement of the remaining milestones was deemed to be not probable as of September 30, 2015 and therefore no expense has been recognized related to these awards. During the three and nine months ended September 30, 2015, the Company recognized stock-based compensation expense of $1.4 million and $4.8 million, respectively, related to stock options with performance-based vesting criteria. During the three and nine months ended September 30, 2014, the Company recognized no stock-based compensation expense related to stock options with performance-based vesting criteria.

All awards are exercisable from the date of grant for a period of ten years.

The stock-based compensation expense recognized during the three and nine months ended September 30, 2015 and 2014 was as follows (amounts in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Stock compensation expense:
Research and development	$	1,472	$	294	$	4,293	$	553
General and administrative		2,935		396		6,861		633

	$	4,407	$	690	$	11,154	$	1,186

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 over the requisite service period of the awards. The weighted average grant date exercise price per share relating to outstanding stock options granted under the Company’s stock option plans during the nine months ended September 30, 2015 and 2014 was $45.27 and $9.08, respectively. The weighted average Black-Scholes value per share relating to outstanding stock options granted under the Company’s stock option plans during the nine months ended September 30, 2015 was $33.44.

The fair value of each option granted to employees and directors during the three and nine months ended September 30, 2015 and 2014 under the Company’s stock option plans has been calculated on the date of grant using the following weighted average assumptions:

Black-Scholes Assumptions:


	Three Months Ended September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014
Expected dividend yield		0	%		0	%		0	%		0	%
Expected volatility		86.59	%		100.43	%		91.03	%		101.07	%
Risk free interest rate		1.80	%		1.99	%		1.57	%		1.90	%
Expected term		6.08 years			5.96 years			6.03 years			6.01 years

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
Outstanding as of December 31, 2014		1,996,615		$	7.01		8.98	$	59,362
Granted		1,369,807			45.27
Exercised		(411,349	)		1.30				28,184
Forfeited		(84,261	)		26.31				1,644

Outstanding as of September 30, 2015		2,870,812		$	25.52		8.86	$	55,937

Vested or expected to vest as of September 30, 2015		2,236,739		$	23.58		8.78	$	48,431

Exercisable as of September 30, 2015		565,941		$	14.74		8.56	$	15,607

As of September 30, 2015, the Company had unrecognized stock-based compensation expense related to its unvested stock option awards of $29.6 million, which is expected to be recognized over the remaining weighted average vesting period of 3.08 years. The total fair value of shares vested for the nine months ended September 30, 2015 and 2014 was $7.3 million and $0.6 million, respectively. During the nine months ended September 30, 2015 and 2014, stock option exercises resulted in proceeds of $0.5 million and $39,379, respectively. The intrinsic value of stock options exercised during the nine months ended September 30, 2015 and 2014 was $28.2 million and $2.4 million, respectively.

Restricted Stock Awards

The Company has granted restricted stock awards to certain officers, employees, directors, and consultants of the Company. During the three months ended September 30, 2015 and 2014, the Company recorded $0.1 million of stock-based compensation expense related to its restricted stock. During the nine months ended September 30, 2015 and 2014, the Company recorded $0.2 million and $0.1 million, 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		(99,513	)
Forfeited		—
Repurchased		—

Outstanding as of September 30, 2015		71,319

As of September 30, 2015 and 2014, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock awards of $0.1 million and $0.4 million, respectively, which is expected to be recognized over the remaining weighted average vesting period of 0.49 years and 1.39 years, respectively

Unvested shares are subject to repurchase by the Company, at the issuance price, upon the employee’s termination at the Company’s sole discretion. No shares of restricted stock were repurchased in the nine months ended September 30, 2015.

Net Loss Per Share

9 Months Ended

Sep. 30, 2015

Earnings Per Share [Abstract]

Net Loss Per Share

6. Net Loss Per Share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the three and nine months ended September 30, 2015 and 2014 (in thousands, except share and per share data):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014
Basic net loss per share attributable to common stockholders:
Numerator:
Net loss	$	(24,035	)	$	(9,859	)	$	(65,933	)	$	(23,744	)

Denominator:
Weighted average common shares outstanding—basic and diluted		28,737,743			19,581,624			27,430,275			7,711,038

Net loss per share attributable to common stockholders—basic and diluted	$	(0.84	)	$	(0.50	)	$	(2.40	)	$	(3.08	)

The following common stock equivalents outstanding as of September 30, 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:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Options to purchase common stock		2,510,900		1,580,223		2,510,900		1,580,223
Employee Stock Purchase Plan		2,803		—		2,803		—
Restricted stock		71,319		202,986		71,319		202,986

		2,585,022		1,783,209		2,585,022		1,783,209

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Income Taxes	7. Income Taxes The Company did not record a federal or state income tax benefit for the Company’s losses for the three and nine months ended September 30, 2015 and 2014 due to the Company’s conclusion that a valuation allowance is required.

Subsequent Event	9 Months Ended
Subsequent Event	Sep. 30, 2015
Subsequent Events [Abstract]
Subsequent Event	8. Subsequent Event In October 2015, the Company entered into a Third Amendment to Lease, effective as of September 9, 2015, and a Fourth Amendment to Lease, effective as of October 27, 2015, with ARE-MA Region No. 38 (“Landlord”) under which the Company increased the amount of rented space under the lease for its 215 First Street, Cambridge, MA offices and extended the term through February, 2022. The increase in future expected payments under these amendments total $6.6 million.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2015

Accounting Policies [Abstract]

Basis of Presentation

Basis of Presentation

Principles of Consolidation

Principles of Consolidation

Recently Issued Accounting Pronouncements

Recently Issued Accounting Pronouncements

Use of Estimates

Use of Estimates

Fair Value Measurements

Fair Value Measurements


Level 1	-	Quoted market prices in active markets for identical assets or liabilities. At September 30, 2015 and December 31, 2014, the Company’s Level 1 assets consisted of money market funds totaling $204.9 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 September 30, 2015 and December 31, 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 September 30, 2015 and December 31, 2014, the Company had no Level 3 assets or liabilities.

Deferred Offering Costs

Deferred Offering Costs

Segment Data

Segment Data

Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2015

Text Block [Abstract]

Summary of Accrued Expenses

Accrued expenses consist of the following (amounts in thousands):


	September 30, 2015		December 31, 2014

Development costs	$	4,096	$	2,788
Employee-related expenses		1,545		1,279
Professional services		756		574
Other accrued expenses		7		46

	$	6,404	$	4,687

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2015

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

Summary of Recognized Stock-Based Compensation Expense

The stock-based compensation expense recognized during the three and nine months ended September 30, 2015 and 2014 was as follows (amounts in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Stock compensation expense:
Research and development	$	1,472	$	294	$	4,293	$	553
General and administrative		2,935		396		6,861		633

	$	4,407	$	690	$	11,154	$	1,186

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

Black-Scholes Assumptions:


	Three Months Ended September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014
Expected dividend yield		0	%		0	%		0	%		0	%
Expected volatility		86.59	%		100.43	%		91.03	%		101.07	%
Risk free interest rate		1.80	%		1.99	%		1.57	%		1.90	%
Expected term		6.08 years			5.96 years			6.03 years			6.01 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
Outstanding as of December 31, 2014		1,996,615		$	7.01		8.98	$	59,362
Granted		1,369,807			45.27
Exercised		(411,349	)		1.30				28,184
Forfeited		(84,261	)		26.31				1,644

Outstanding as of September 30, 2015		2,870,812		$	25.52		8.86	$	55,937

Vested or expected to vest as of September 30, 2015		2,236,739		$	23.58		8.78	$	48,431

Exercisable as of September 30, 2015		565,941		$	14.74		8.56	$	15,607

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		(99,513	)
Forfeited		—
Repurchased		—

Outstanding as of September 30, 2015		71,319

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2015

Earnings Per Share [Abstract]

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


	Three Months Ended September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014
Basic net loss per share attributable to common stockholders:
Numerator:
Net loss	$	(24,035	)	$	(9,859	)	$	(65,933	)	$	(23,744	)

Denominator:
Weighted average common shares outstanding—basic and diluted		28,737,743			19,581,624			27,430,275			7,711,038

Net loss per share attributable to common stockholders—basic and diluted	$	(0.84	)	$	(0.50	)	$	(2.40	)	$	(3.08	)

Summary of Common Stock Equivalents Outstanding


	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Options to purchase common stock		2,510,900		1,580,223		2,510,900		1,580,223
Employee Stock Purchase Plan		2,803		—		2,803		—
Restricted stock		71,319		202,986		71,319		202,986

		2,585,022		1,783,209		2,585,022		1,783,209

Nature of Operations - Additional Information (Detail) - USD ($) $ in Thousands			9 Months Ended
	Apr. 20, 2015	Jul. 23, 2014	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Nature Of Operations [Line Items]
Accumulated deficit			$ (132,778)	$ (66,845)
Net proceeds from sale of common stock		$ 94,000
Cash balance			204,877	$ 127,766	$ 136,727	$ 8,066
Proceeds from underwritten initial public offering of common stock, net proceeds	$ 129,100
Redeemable Convertible Preferred Stock [Member]
Nature Of Operations [Line Items]
Convertible preferred stock proceeds raised			$ 90,600

Summary of Significant Accounting Policies - Additional Information (Detail)				9 Months Ended
	Apr. 20, 2015 USD ($) $ / shares shares	Jul. 23, 2014 USD ($) $ / shares shares	Jul. 02, 2014	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
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
Payment of offering costs	$ 600,000	$ 2,300,000		$ 548,000	$ 2,035,000
Fair Value, Inputs, Level 1 [Member] \| Money Market Funds [Member]
Summary Of Significant Accounting Policies [Line Items]
Assets fair value				204,900,000		$ 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
IPO [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

Accrued Expenses - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Development costs	$ 4,096	$ 2,788
Employee related expenses	1,545	1,279
Professional services	756	574
Other accrued expenses	7	46
Total accrued expenses	$ 6,404	$ 4,687

Commitments and Contingencies - CyDex License Agreement - Additional Information (Detail) - CyDex License Agreement [Member] - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense	$ 0.1
First and Second Clinical Development Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	0.8
First and Second Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	3.8
Third and Fourth Clinical Development Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	1.3
Third and Fourth Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	8.5
Clinical Development [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense		$ 0.5	$ 0.3
Expected milestone payments	0.8
Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 1.8

Commitments and Contingencies - Washington University License Agreement - Additional Information (Detail) - Washington University License Agreement [Member] - USD ($)	1 Months Ended	9 Months Ended	12 Months Ended
	Nov. 30, 2013	Sep. 30, 2015	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

Commitments and Contingencies - University of California License Agreements - Additional Information (Detail) - University of California License Agreements [Member] - USD ($)	1 Months Ended	3 Months Ended			9 Months Ended
	Jun. 30, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2015	Oct. 31, 2013
Commitments And Contingencies [Line Items]
License payment description					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.
Percentage of net sales					1.00%
Licenses Expiration period, maximum					27 years
Licenses Expiration period, minimum					15 years
Upfront payment	$ 50,000
Annual license maintenance fee	15,000
Clinical Development [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments						$ 100,000
Research and development expense related to milestone expense		$ 25,000	$ 25,000	$ 100,000
Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	700,000		700,000
Sales Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 2,000,000		$ 2,000,000

Commitments and Contingencies - Consulting Agreement - Additional Information (Detail) - Consulting Agreement [Member] - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	Jan. 31, 2014	Jun. 30, 2015	Mar. 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 Clinical Development Milestones [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense			$ 600,000
Milestone payments			200,000
Payments for stock issued upon reaching a milestone			$ 400,000
Milestone based share compensation, shares issued			7,936
Third Clinical Development Milestones [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense		$ 1,100,000
Milestone payments		300,000
Payments for stock issued upon reaching a milestone		$ 800,000
Milestone based share compensation, shares issued		15,873

Stock-Based Compensation - Additional Information (Detail) - USD ($)			3 Months Ended		9 Months Ended
	Jan. 01, 2015	Jul. 02, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 4,407,000	$ 690,000	$ 11,154,000	$ 1,186,000
Contractual term, option					10 years
Proceeds from stock options exercised					$ 663,000	$ 39,000
2014 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance under 2014 Stock Option Plan	773,779		997,486		997,486
Percentage of increase on issued and outstanding shares of Common stock	3.00%
Percentage of performance based grants that were achieved					35.00%
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
Proceeds from issuance of common stock under the Employee Stock Purchase Plan					$ 100,000
Share based compensation granted under plan vest period					4 years
Share based compensation, vest period					1 year
Contractual term, option					10 years
Weighted average grant date fair value per share					$ 45.27	$ 9.08
2014 Employee Stock Purchase Plan [Member] \| Black Scholes Stock Price Valuation Model [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value per share					$ 33.44
2014 Employee Stock Purchase Plan [Member] \| 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			3,868,298		3,868,298
2011 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option grant					0
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 100,000	100,000	$ 200,000	$ 100,000
Unrecognized stock-based compensation expense			100,000	400,000	$ 100,000	$ 400,000
Weighted average period of unrecognized compensation costs					5 months 27 days	1 year 4 months 21 days
Stock repurchased, shares					0
Performance Milestone [Member] \| 2014 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options with performance-based criteria					497,100
Stock-based compensation expense			1,400,000	$ 0	$ 4,800,000	$ 0
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option grant					1,369,807
Unrecognized stock-based compensation expense			$ 29,600,000		$ 29,600,000
Weighted average period of unrecognized compensation costs					3 years 29 days
Total fair value of shares vested					$ 7,300,000	600,000
Proceeds from stock options exercised					500,000	39,379,000
Intrinsic value of options exercised					$ 28,184,000	$ 2,400,000

Stock-Based Compensation - Summary of Recognized Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 4,407	$ 690	$ 11,154	$ 1,186
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	1,472	294	4,293	553
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 2,935	$ 396	$ 6,861	$ 633

Stock-Based Compensation - Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected volatility	86.59%	100.43%	91.03%	101.07%
Risk free interest rate	1.80%	1.99%	1.57%	1.90%
Expected term	6 years 29 days	5 years 11 months 16 days	6 years 11 days	6 years 4 days

Stock-Based Compensation - Summary of Activity Relating to Stock Options (Detail) - Options to Purchase Common Stock [Member] - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Stock options	1,996,615
Granted, Stock options	1,369,807
Exercised, Stock options	(411,349)
Forfeited, Stock options	(84,261)
Ending balance, Outstanding Shares-Stock options	2,870,812		1,996,615
Vested or expected to vest, Stock options	2,236,739
Exercisable, Stock options	565,941
Beginning balance, Weighted Average Exercise Price-Stock options	$ 7.01
Granted, Weighted Average Exercise Price-Stock options	45.27
Exercised, Weighted Average Exercise Price-Stock options	1.30
Forfeited, Weighted Average Exercise Price-Stock options	26.31
Ending balance, Outstanding Weighted Average Exercise Price-Stock options	25.52		$ 7.01
Vested or expected to vest, Weighted Average Exercise Price-Stock options	23.58
Exercisable, Weighted Average Exercise Price-Stock options	$ 14.74
Outstanding, Weighted Average Remaining Life-Stock options	8 years 10 months 10 days		8 years 11 months 23 days
Vested or expected to vest, Weighted Average Remaining Life-Stock options	8 years 9 months 11 days
Exercisable, Weighted Average Remaining Life-Stock options	8 years 6 months 22 days
Exercised, Aggregate Intrinsic Value-Stock options	$ 28,184	$ 2,400
Forfeited, Aggregate Intrinsic Value-Stock options	1,644
Outstanding, Aggregate Intrinsic Value-Stock options	55,937		$ 59,362
Vested or expected to vest, Aggregate Intrinsic Value-Stock options	48,431
Exercisable, Aggregate Intrinsic Value-Stock options	$ 15,607

Stock-Based Compensation - Summary of Activity Relating to Restricted Stock (Detail) - Restricted Stock [Member]	9 Months Ended
	Sep. 30, 2015 shares
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
Vested, Shares-Restricted stock	(99,513)
Forfeited, Shares-Restricted stock	0
Repurchased, Shares-Restricted stock	0
Outstanding, Shares at ending balance-Restricted stock	71,319

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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net loss	$ (24,035)	$ (9,859)	$ (65,933)	$ (23,744)
Denominator:
Weighted average common shares outstanding-basic and diluted	28,737,743	19,581,624	27,430,275	7,711,038
Net loss per share attributable to common stockholders-basic and diluted	$ (0.84)	$ (0.50)	$ (2.40)	$ (3.08)

Net Loss Per Share - Summary of Common Stock Equivalents Outstanding (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	2,585,022	1,783,209	2,585,022	1,783,209
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	2,510,900	1,580,223	2,510,900	1,580,223
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	2,803		2,803
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	71,319	202,986	71,319	202,986

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Tax Disclosure [Abstract]
State income tax benefit	$ 0	$ 0	$ 0	$ 0
Federal income tax benefit	$ 0	$ 0	$ 0	$ 0

Subsequent Event - Additional Information (Detail) $ in Millions	Oct. 27, 2015 USD ($)
Subsequent Event [Member]
Subsequent Event [Line Items]
Future expected payments	$ 6.6