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Quoted market prices in active markets for identical assets or liabilities.

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.

Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2016	Aug. 01, 2016
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2016
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q2
Trading Symbol	SAGE
Entity Registrant Name	Sage Therapeutics, Inc.
Entity Central Index Key	0001597553
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		32,094,020

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 189,003	$ 186,753
Marketable securities	83,292	0
Prepaid expenses and other current assets	1,812	1,738
Total current assets	274,107	188,491
Property and equipment, net	959	286
Restricted cash	564	39
Deferred offering costs		200
Total assets	275,630	189,016
Current liabilities:
Accounts payable	5,957	5,159
Accrued expenses	12,382	10,148
Total current liabilities	18,339	15,307
Other liabilities	82	14
Total liabilities	18,421	15,321
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at June 30, 2016 and December 31, 2015, respectively; no shares issued or outstanding at June 30, 2016 and December 31, 2015, respectively
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at June 30, 2016 and December 31, 2015, respectively; 32,073,437 and 28,823,549 shares issued and outstanding at June 30, 2016 and December 31, 2015, respectively	3	3
Additional paid-in capital	483,797	335,032
Accumulated deficit	(226,630)	(161,340)
Accumulated other comprehensive items	39
Total stockholders' equity	257,209	173,695
Total liabilities and stockholders' equity	$ 275,630	$ 189,016

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2016	Dec. 31, 2015
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	32,073,437	28,823,549
Common stock, shares outstanding	32,073,437	28,823,549

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Operating expenses:
Research and development	$ 26,096	$ 18,603	$ 49,677	$ 31,503
General and administrative	8,910	6,456	16,044	10,453
Total operating expenses	35,006	25,059	65,721	41,956
Loss from operations	(35,006)	(25,059)	(65,721)	(41,956)
Interest income, net	266	41	442	62
Other expense, net	(7)	(9)	(11)	(4)
Net loss	$ (34,747)	$ (25,027)	$ (65,290)	$ (41,898)
Net loss per share-basic and diluted	$ (1.08)	$ (0.90)	$ (2.05)	$ (1.57)
Weighted average shares outstanding-basic and diluted	32,062,298	27,860,332	31,835,194	26,765,705
Comprehensive loss:
Net loss	$ (34,747)	$ (25,027)	$ (65,290)	$ (41,898)
Other comprehensive items:
Unrealized gain on marketable securities	39		39
Total other comprehensive gain	39		39
Total comprehensive loss	$ (34,708)	$ (25,027)	$ (65,251)	$ (41,898)

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities
Net loss	$ (65,290)	$ (41,898)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	8,179	6,747
Non-cash licensing and consulting fees		1,211
Premium on marketable securities	(269)
Amortization of premium on marketable securities	13
Depreciation	116	54
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(74)	(2,219)
Accounts payable	941	2,760
Accrued expenses and other liabilities	2,278	296
Net cash used in operating activities	(54,106)	(33,049)
Cash flows from investing activities
Purchases of marketable securities	(82,997)
Purchases of property and equipment	(835)	(181)
Increase in restricted cash	(525)
Net cash used in investing activities	(84,357)	(181)
Cash flows from financing activities
Proceeds from stock option exercises and employee stock purchase plan issuances	312	436
Payments of offering costs	(599)	(458)
Proceeds from public offerings of common stock, net of commissions and underwriting discounts	141,000	129,720
Net cash provided by financing activities	140,713	129,698
Net increase in cash and cash equivalents	2,250	96,468
Cash and cash equivalents at beginning of period	186,753	127,766
Cash and cash equivalents at end of period	$ 189,003	224,234
Supplemental disclosure of non-cash financing activities
Public offering costs included in accounts payable or accrued expenses		$ 137

Nature of Operations	6 Months Ended
Nature of Operations	Jun. 30, 2016
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. 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 it is 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 June 30, 2016, the Company had an accumulated deficit of $226.6 million. From its inception through June 30, 2016, the Company received net proceeds of $454.1 million from the sales of redeemable convertible preferred stock, the issuance of convertible notes, and the proceeds from its initial public offering (“IPO”) in July 2014 and follow-on underwritten public offerings in April 2015 and January 2016. Based on its current operating plans, the Company believes its cash, cash equivalents and marketable securities of $272.3 million as of June 30, 2016 will be sufficient to fund its anticipated level of operations and capital expenditures into late 2017.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2016

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, 2015.

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 condensed consolidated financial statements contain all adjustments, consisting of only normal recurring adjustments, necessary for a fair statement of its financial position as of June 30, 2016, its results of operations and comprehensive loss for the three and six months ended June 30, 2016, and its cash flows for the six months ended June 30, 2016 and 2015. The condensed consolidated balance sheet at December 31, 2015 was derived from audited financial statements, but does not contain all of the footnote disclosures from the annual financial statements. The results for the three and six months ended June 30, 2016 are not necessarily indicative of the results for the year ending December 31, 2016, or for any future period.

Principles of Consolidation

The unaudited interim 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, 2015. Intercompany accounts and transactions have been eliminated.

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.

Marketable securities

Marketable securities consist of investments with original maturities greater than ninety days. The Company considers its investment portfolio of investments to be available-for-sale. Accordingly, these investments are recorded at fair value, which is based on quoted market prices. Unrealized gains and losses are reported as a component of accumulated other comprehensive items in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other expense, net, based on the specific identification method. When determining whether a decline in value is other than temporary, the Company considers various factors, including whether the Company has the intent to sell the security, and whether it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost 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:

The Company’s cash equivalents and marketable securities at June 30, 2016 and December 31, 2015 were carried at fair value, determined according to the fair value hierarchy; see Footnote 3, Fair Value Measurements.

The carrying amounts reflected in the unaudited condensed consolidated balance sheets for accounts payable and accrued expenses approximate their fair values due to their short-term maturities at June 30, 2016 and December 31, 2015, 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 deferred offering costs until such financings are consummated. After consummation of the follow-on public offerings of common stock in January 2016 and April 2015, $0.6 million and $0.6 million, respectively, of these costs were recorded in stockholders’ equity as a reduction of additional paid-in capital generated as a result of the offering.

Restricted Cash

A deposit of $0.5 million was restricted from withdrawal as of June 30, 2016. The restriction is related to securing the Company’s facility lease in May 2016, under which the Company will rent 19,805 square feet of additional office space in a separate multi-tenant building beginning in September 2016. The lease for the additional space will expire in February 2022. The restriction expires in 2022, in accordance with the operating lease agreement. This balance is included in restricted cash on the accompanying unaudited condensed consolidated balance sheets.

Recently Issued Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (“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 Accounting Standards Update, or ASU, 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40). The 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 year ending December 31, 2016. Early adoption is permitted. The Company does not expect that the adoption of this new guidance will have a material impact on its consolidated financial statements.

In February 2016, the 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 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 similarly 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 that this new guidance will have on its consolidated financial statements.

In March 2016, the FASB issued ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. The standard involves several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. The new standard will be effective on January 1, 2017. The Company is in the process of evaluating the impact that this new guidance will have on its consolidated financial statements.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The standard changes the impairment model for most financial assets and certain other instruments. Under the standard, entities holding financial assets and net investment in leases that are not accounted for at fair value through net income are to be presented at the net amount expected to be collected. An allowance for credit losses will be a valuation account that will be deducted from the amortized cost basis of the financial asset to present the net carrying value at the amount expected to be collected on the financial asset. The new standard will be effective on January 1, 2020. The Company is in the process of evaluating the impact that this new guidance will have on its consolidated financial statements.

Fair Value Measurements

6 Months Ended

Jun. 30, 2016

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The Company’s cash equivalents are generally classified within Level 1 of the fair value hierarchy. The Company’s investments in marketable securities are classified within Level 2 of the fair value hierarchy.

The fair values of the Company’s marketable securities are generally based on prices obtained from independent pricing sources. Consistent with the fair value hierarchy described above, securities with validated quotes from pricing services are generally reflected within Level 2, as they are primarily based on observable pricing for similar assets and/or other market observable inputs. Typical inputs used by these pricing services include, but are not limited to, reported trades, benchmark yields, issuer spreads, bids, offers and/or estimates cash flow, prepayment spreads and default rates.

The following tables summarize the Company’s cash, cash equivalents and marketable securities as of June 30, 2016 and December 31, 2015:


	June 30, 2016
	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash and cash equivalents:
Money market funds	$	189,003	$	189,003	$	—	$	—

Total cash and cash equivalents		189,003		189,003		—		—

Marketable securities:
U.S. government securities		32,082		—		32,082		—
Corporate bonds		28,788		—		28,788		—
Commercial paper		22,422		—		22,422		—

Total marketable securities		83,292		—		83,292		—

Total cash, cash equivalents and marketable securities	$	272,295	$	189,003	$	83,292	$	—


	December 31, 2015
	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash and cash equivalents:
Money market funds	$	186,753	$	186,753	$	—	$	—

Total cash and cash equivalents	$	186,753	$	186,753	$	—	$	—

During the three and six months ended June 30, 2016 and 2015, there were no transfers among the Level 1, Level 2 and Level 3 categories.

The carrying amounts reflected in the consolidated balance sheets for accounts payable and accrued expenses approximate fair value due to their short-term maturities.

Marketable Securities

The following table summarizes the Company’s marketable securities as of June 30, 2016.


	June 30, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Assets:
U.S. government securities (due within 1 year)	$	32,053	$	29	$	—		$	32,082
Corporate bonds (due within 1 year)		28,778		18		(8	)		28,788
Commercial paper (due within 1 year)		22,422		—		—			22,422

	$	83,253	$	47	$	(8	)	$	83,292

There have been no impairments of the Company’s assets measured and carried at fair value during the three and six months ended June 30, 2016 and 2015. The Company held no marketable securities as of December 31, 2015.

Accrued Expenses

6 Months Ended

Jun. 30, 2016

Text Block [Abstract]

Accrued Expenses

4. Accrued Expenses

Accrued expenses consist of the following:


	June 30, 2016		December 31, 2015
	(in thousands)
Development costs	$	9,567	$	6,466
Employee-related expenses		2,073		2,718
Professional services		738		935
Other accrued expenses		4		29

	$	12,382	$	10,148

Commitments and contingencies	6 Months Ended
Commitments and contingencies	Jun. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	5. Commitments and contingencies *Operating Leases* The Company rents 22,067 square feet of office space in a multi-tenant building under an operating lease that will expire in February 2022. In May 2016, the Company entered into a lease under which the Company will rent 19,805 square feet of additional office space in a separate multi-tenant building beginning on September 1, 2016. The lease for the additional space will also expire in February 2022. A deposit of $0.5 million was restricted from withdrawal as of June 30, 2016, which is related to securing the lease. The restriction expires in 2022, in accordance with the operating lease agreement. This balance is included in restricted cash on the accompanying unaudited condensed consolidated balance sheets. *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 the 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 up to $0.8 million in clinical milestones and up to $3.8 million in regulatory milestones for each of the first two fields with respect to SAGE-547; up to $1.3 million in clinical milestones and up to $8.5 million in regulatory milestones for each of the third and fourth fields with respect to SAGE-547; and up to $0.8 million in clinical milestones and up to $1.8 million in regulatory milestones for one field with respect to SAGE-689. 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 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 June 30, 2015 of $0.5 million. For the three and six months ended June 30, 2016, the Company did not record any expense or make any milestone or royalty payments under the license agreement with CyDex. *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 of $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 and made a cash payment of $50,000. For the three and six months ended June 30, 2016, the Company did not record any expense or make any milestone payments under the license agreement with Washington University. *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 paid to The Regents of the University of California clinical development milestones of up to $0.1 million and will be required to pay royalties of less than 1% on net sales for a period of fifteen years following the sale of the first 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. During the three months ended March 31, 2015, one clinical development milestone was met. Accordingly, the Company recorded research and development expenses and made cash payments totaling $0.1 million. During the three months ended June 30, 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 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 payments of $15,000 for annual maintenance fees until the calendar year following the first sale, if any, of a licensed product. The Company is obligated to make milestone payments following the achievement of specified regulatory and sales milestones of up to $0.7 million and $2.0 million in the aggregate, respectively. 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. For the three and six months ended June 30, 2016, the Company did not record any expense or make any milestone or royalty payments under either license agreement with The Regents of the University of California. *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 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, related to the achievement of this milestone. 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, related to the achievement of this milestone. For the three and six months ended June 30, 2016, the Company did not record any expense or make any milestone payments under the consulting agreement with the nonemployee advisor.

Sale of Equity Securities	6 Months Ended
Sale of Equity Securities	Jun. 30, 2016
Other Liabilities Disclosure [Abstract]
Sale of Equity Securities	6. Sale of Equity Securities 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 offering expenses paid by the Company.

Stock-Based Compensation

6 Months Ended

Jun. 30, 2016

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

Stock-Based Compensation

7. Stock-Based Compensation

Stock Option Plans

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 June 30, 2016, the total number of shares reserved under all equity plans is 4,959,683, and the Company had 1,081,131 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. On January 1, 2016, 1,154,653 shares of common stock, representing 4% of the Company’s issued and outstanding shares of common stock as of December 31, 2015, were added to the 2014 Stock Option Plan.

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 continued service of the grantee 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 employee awards. All awards expire in ten years.

During the six months ended June 30, 2016 and 2015, the Company granted 74,039 and 497,100 options, respectively, 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 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 three months ended June 30, 2015, the achievement of one milestone was considered probable and that milestone was achieved during the three months ended September 30, 2015. The estimated quantity of awards expected to vest was recognized by determining the cumulative expense as of June 30, 2015 and the remaining expense was recognized over the estimated service period. This milestone represents 35% of the performance-based option grants that were made during 2015. During the three and six months ended June 30, 2015, the Company recognized stock-based compensation expense of $3.4 million related to stock options with performance-based vesting criteria.

The achievement of the remaining milestones was deemed to be not probable as of June 30, 2016 and therefore no expense has been recognized related to these awards for the three and six months ended June 30, 2016.

Stock-based compensation expense recognized during the three and six months ended June 30, 2016 and 2015 was as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2016		2015		2016		2015
	(in thousands)
Research and development	$	2,037	$	2,298	$	3,649	$	2,821
General and administrative		2,428		3,100	$	4,530		3,926

	$	4,465	$	5,398	$	8,179	$	6,747

For stock option awards, the fair value 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. The weighted average grant date fair value per share relating to outstanding stock options granted under the Company’s stock option plans during the six months ended June 30, 2016 and 2015 was $22.23 and $41.68, respectively.

The fair value of each option granted to employees and nonemployee directors during the three and six months ended June 30, 2016 and 2015, under the Company’s stock option plans has been calculated on the date of grant using the following weighted average assumptions:


	Three Months Ended June 30,						Six Months Ended June 30,
	2016			2015			2016			2015
Expected dividend yield		0	%		0	%		0	%		0	%
Expected volatility		80.73	%		88.58	%		80.11	%		92.44	%
Risk free interest rate		1.42	%		1.69	%		1.41	%		1.49	%
Expected term		6.06 years			5.71 years			6.06 years			5.87 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: The Company does not have sufficient history to support a calculation of volatility using only its historical data. As such, the Company has used a weighted-average volatility considering the Company’s own volatility since the IPO in July 2014 and the volatilities of 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 publicly traded 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 options granted 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 six months ended June 30, 2016 and 2015, forfeiture rates of 9.6% and 10.0%, respectively, were 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, 2015		3,002,809		$	26.67		8.67	$	96,479
Granted		969,785			32.25
Exercised		(57,142	)		1.47
Forfeited		(36,900	)		56.07

Outstanding as of June 30, 2016		3,878,552		$	28.16		8.55	$	34,015

Vested and expected to vest as of June 30, 2016		3,168,000		$	26.93		8.49	$	31,690

Exercisable as of June 30, 2016		1,135,287		$	20.40		7.91	$	17,403

At June 30, 2016, the Company had unrecognized stock-based compensation expense related to its unvested service-based stock option awards of $39.6 million, which is expected to be recognized over the remaining weighted average vesting period of 2.9 years. The total fair value of shares vested for the six months ended June 30, 2016 and 2015 was $9.7 million and $1.7 million, respectively. In addition, the Company has 433,015 outstanding unvested stock options that vest upon the achievement of certain performance criteria. Total unrecognized stock-based compensation expense related to those awards was $9.1 million at June 30, 2016.

The intrinsic value of stock options exercised during the six months ended June 30, 2016 and 2015 was $2.3 million and $19.9 million, respectively.

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 three months ended June 30, 2016 and 2015, the Company recorded $15,000 and $0.1 million, respectively, of stock-based compensation expense related to its restricted stock. During the six months ended June 30, 2016 and 2015, the Company recorded $31,000 and $0.2 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, 2015		42,781
Issued		—
Vested		(31,545	)
Forfeited		—
Repurchased		—

Outstanding as of June 30, 2016		11,236

At June 30, 2016, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock awards of $4,000 which is expected to be recognized over the remaining weighted average vesting period of 0.11 years.

During the six months ended June 30, 2016 and 2015, no shares of restricted stock were issued.

Unvested shares are subject to repurchase by the Company, at the issuance price, upon the termination of the employee at the sole discretion of the Company. No shares were repurchased during the six months ended June 30, 2016 and 2015.

2014 Employee Stock Purchase Plan

On July 2, 2014, the Company’s stockholders approved the 2014 Employee Stock Purchase Plan, which had been previously approved by the Board of Directors. 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 June 30, 2016, 7,159 shares have been issued under this plan.

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References + Details

Net Loss Per Share

6 Months Ended

Jun. 30, 2016

Earnings Per Share [Abstract]

Net Loss Per Share

8. Net Loss Per Share

Basic and diluted net loss per share was calculated as follows for the three and six months ended June 30, 2016 and 2015:


	Three Months Ended June 30,						Six Months Ended June 30,
	2016			2015			2016			2015
Basic net loss per share:
Numerator:
Net loss (in thousands)	$	(34,747	)	$	(25,027	)	$	(65,290	)	$	(41,898	)

Denominator:
Weighted average common stock outstanding—basic		32,062,298			27,860,332			31,835,194			26,765,705
Dilutive effect of shares of common stock equivalents resulting from common stock options		—			—			—			—

Weighted average common stock outstanding—diluted		32,062,298			27,860,332			31,835,194			26,765,705

Net loss per share—basic and diluted	$	(1.08	)	$	(0.90	)	$	(2.05	)	$	(1.57	)

The following common stock equivalents outstanding as of June 30, 2016 and 2015 were excluded from the computation of diluted net loss per share for the periods presented because including them would have been anti-dilutive:


	Three Months Ended June 30,				Six Months Ended June 30,
	2016		2015		2016		2015
Options to purchase common stock		3,445,537		1,643,654		3,445,537		1,643,654
Employee stock purchase plan		7,192		1,500		7,192		1,500
Restricted stock		11,236		104,220		11,236		104,220

		3,463,965		1,749,374		3,463,965		1,749,374

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2016

Accounting Policies [Abstract]

Basis of Presentation

Basis of Presentation

Principles of Consolidation

Principles of Consolidation

Use of Estimates

Use of Estimates

Marketable securities

Marketable securities

Fair Value Measurements

Fair Value Measurements

Deferred Offering Costs

Deferred Offering Costs

Restricted Cash

Restricted Cash

Recently Issued Accounting Pronouncements

Recently Issued Accounting Pronouncements

- Definition

Disclosure of accounting policy for investments in debt and equity securities that have readily determinable fair values (marketable securities). At a minimum, the disclosure might address accounting policies for investments classified as trading, available for sale, or held to maturity and may include how the entity determines whether impairments of available for sale or held to maturity investments are other than temporary, how the fair values of the entity's securities are determined, and the entity's accounting treatment for transfers between investment categories.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.M)
-URI http://asc.fasb.org/extlink&oid=65877573&loc=d3e87990-122713

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=68058157&loc=d3e18780-107790

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Readily Determinable Fair Value
-URI http://asc.fasb.org/extlink&oid=65888395

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section S50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6381980&loc=d3e87707-122711

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62652-112803

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(5))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2016

Fair Value Disclosures [Abstract]

Summary of Company's Cash, Cash Equivalents and Marketable Securities

The following tables summarize the Company’s cash, cash equivalents and marketable securities as of June 30, 2016 and December 31, 2015:


	June 30, 2016
	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash and cash equivalents:
Money market funds	$	189,003	$	189,003	$	—	$	—

Total cash and cash equivalents		189,003		189,003		—		—

Marketable securities:
U.S. government securities		32,082		—		32,082		—
Corporate bonds		28,788		—		28,788		—
Commercial paper		22,422		—		22,422		—

Total marketable securities		83,292		—		83,292		—

Total cash, cash equivalents and marketable securities	$	272,295	$	189,003	$	83,292	$	—


	December 31, 2015
	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash and cash equivalents:
Money market funds	$	186,753	$	186,753	$	—	$	—

Total cash and cash equivalents	$	186,753	$	186,753	$	—	$	—

Summary of Marketable Securities

The following table summarizes the Company’s marketable securities as of June 30, 2016.


	June 30, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Assets:
U.S. government securities (due within 1 year)	$	32,053	$	29	$	—		$	32,082
Corporate bonds (due within 1 year)		28,778		18		(8	)		28,788
Commercial paper (due within 1 year)		22,422		—		—			22,422

	$	83,253	$	47	$	(8	)	$	83,292

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Accrued Expenses (Tables)

6 Months Ended

Jun. 30, 2016

Text Block [Abstract]

Summary of Accrued Expenses

Accrued expenses consist of the following:


	June 30, 2016		December 31, 2015
	(in thousands)
Development costs	$	9,567	$	6,466
Employee-related expenses		2,073		2,718
Professional services		738		935
Other accrued expenses		4		29

	$	12,382	$	10,148

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2016

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

Summary of Recognized Stock-Based Compensation Expense

Stock-based compensation expense recognized during the three and six months ended June 30, 2016 and 2015 was as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2016		2015		2016		2015
	(in thousands)
Research and development	$	2,037	$	2,298	$	3,649	$	2,821
General and administrative		2,428		3,100	$	4,530		3,926

	$	4,465	$	5,398	$	8,179	$	6,747

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


	Three Months Ended June 30,						Six Months Ended June 30,
	2016			2015			2016			2015
Expected dividend yield		0	%		0	%		0	%		0	%
Expected volatility		80.73	%		88.58	%		80.11	%		92.44	%
Risk free interest rate		1.42	%		1.69	%		1.41	%		1.49	%
Expected term		6.06 years			5.71 years			6.06 years			5.87 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, 2015		3,002,809		$	26.67		8.67	$	96,479
Granted		969,785			32.25
Exercised		(57,142	)		1.47
Forfeited		(36,900	)		56.07

Outstanding as of June 30, 2016		3,878,552		$	28.16		8.55	$	34,015

Vested and expected to vest as of June 30, 2016		3,168,000		$	26.93		8.49	$	31,690

Exercisable as of June 30, 2016		1,135,287		$	20.40		7.91	$	17,403

Summary of Activity Relating to Restricted Stock

The table below summarizes activity relating to restricted stock:


	Shares
Outstanding as of December 31, 2015		42,781
Issued		—
Vested		(31,545	)
Forfeited		—
Repurchased		—

Outstanding as of June 30, 2016		11,236

Net Loss Per Share (Tables)

6 Months Ended

Jun. 30, 2016

Earnings Per Share [Abstract]

Summary of Basic and Diluted Net Loss Per Share

Basic and diluted net loss per share was calculated as follows for the three and six months ended June 30, 2016 and 2015:


	Three Months Ended June 30,						Six Months Ended June 30,
	2016			2015			2016			2015
Basic net loss per share:
Numerator:
Net loss (in thousands)	$	(34,747	)	$	(25,027	)	$	(65,290	)	$	(41,898	)

Denominator:
Weighted average common stock outstanding—basic		32,062,298			27,860,332			31,835,194			26,765,705
Dilutive effect of shares of common stock equivalents resulting from common stock options		—			—			—			—

Weighted average common stock outstanding—diluted		32,062,298			27,860,332			31,835,194			26,765,705

Net loss per share—basic and diluted	$	(1.08	)	$	(0.90	)	$	(2.05	)	$	(1.57	)

Summary of Common Stock Equivalents Outstanding


	Three Months Ended June 30,				Six Months Ended June 30,
	2016		2015		2016		2015
Options to purchase common stock		3,445,537		1,643,654		3,445,537		1,643,654
Employee stock purchase plan		7,192		1,500		7,192		1,500
Restricted stock		11,236		104,220		11,236		104,220

		3,463,965		1,749,374		3,463,965		1,749,374

Nature of Operations - Additional Information (Detail) - USD ($) $ in Thousands	75 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Nature Of Operations [Line Items]
Accumulated deficit	$ (226,630)	$ (161,340)
Cash, cash equivalents and marketable securities	272,295
Redeemable Convertible Preferred Stock [Member] \| Convertible Notes [Member] \| Initial Public Offering [Member]
Nature Of Operations [Line Items]
Net proceeds from sale of equity and notes	$ 454,100

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	1 Months Ended			6 Months Ended
	May 31, 2016 ft²	Jan. 31, 2016 USD ($)	Apr. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) ft²	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Payment of offering costs		$ 600	$ 600	$ 599	$ 458
Restricted cash deposit				564		$ 39
Operating Lease One [Member] \| Multi Tenant Building [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash deposit				$ 500
Additional Office space rented under operating lease \| ft²	19,805			22,067

Fair Value Measurements - Summary of Company's Cash, Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total cash and cash equivalents	$ 189,003	$ 186,753	$ 224,234	$ 127,766
Total marketable securities	83,292
Total cash, cash equivalents and marketable securities	272,295
Money Market Funds [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total cash and cash equivalents	189,003	186,753
Corporate Bonds [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total marketable securities	28,788
Commercial Paper [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total marketable securities	22,422
U.S. Government Securities [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total marketable securities	32,082
Fair Value, Inputs, Level 1 [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total cash and cash equivalents	189,003	186,753
Total cash, cash equivalents and marketable securities	189,003
Fair Value, Inputs, Level 1 [Member] \| Money Market Funds [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total cash and cash equivalents	189,003	$ 186,753
Fair Value, Inputs, Level 2 [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total marketable securities	83,292
Total cash, cash equivalents and marketable securities	83,292
Fair Value, Inputs, Level 2 [Member] \| Corporate Bonds [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total marketable securities	28,788
Fair Value, Inputs, Level 2 [Member] \| Commercial Paper [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total marketable securities	22,422
Fair Value, Inputs, Level 2 [Member] \| U.S. Government Securities [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total marketable securities	$ 32,082

Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Debt Instrument Fair Value Carrying Value [Abstract]
Transfers among the Level 1, Level 2 and Level 3 categories	$ 0	$ 0	$ 0	$ 0
Impairment of assets	0	$ 0	0	$ 0
Marketable securities	$ 83,292,000		$ 83,292,000		$ 0

Fair Value Measurements - Summary of Marketable Securities (Detail) $ in Thousands	Jun. 30, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 83,253
Gross Unrealized Gains	47
Gross Unrealized Losses	(8)
Fair Value	83,292
U.S. Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32,053
Gross Unrealized Gains	29
Fair Value	32,082
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	28,778
Gross Unrealized Gains	18
Gross Unrealized Losses	(8)
Fair Value	28,788
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,422
Fair Value	$ 22,422

Fair Value Measurements - Summary of Marketable Securities (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 2016
U.S. Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable securities maturity period	1 year
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable securities maturity period	1 year
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable securities maturity period	1 year

Accrued Expenses - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Payables and Accruals [Abstract]
Development costs	$ 9,567	$ 6,466
Employee-related expenses	2,073	2,718
Professional services	738	935
Other accrued expenses	4	29
Total accrued expenses	$ 12,382	$ 10,148

Commitments and Contingencies - Operating Leases - Additional Information (Detail) $ in Thousands	1 Months Ended	6 Months Ended
	May 31, 2016 ft²	Jun. 30, 2016 USD ($) ft²	Dec. 31, 2015 USD ($)
Commitments And Contingencies [Line Items]
Restricted cash deposit		$ 564	$ 39
Operating Lease One [Member] \| Multi Tenant Building [Member]
Commitments And Contingencies [Line Items]
Office space rented under operating lease \| ft²	19,805	22,067
Lease expire date	Feb. 28, 2022
Commencement date of lease	Sep. 01, 2016
Restricted cash deposit		$ 500

Commitments and Contingencies - CyDex License Agreement - Additional Information (Detail)	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($) Milestone	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Commitments And Contingencies [Line Items]
Research and development expense	$ 26,096,000	$ 18,603,000		$ 49,677,000	$ 31,503,000
CyDex License Agreement [Member]
Commitments And Contingencies [Line Items]
Research and development expense		$ 500,000				$ 100,000
CyDex License Agreement [Member] \| First and Second Clinical Development Milestones [Member] \| Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	800,000			800,000
CyDex License Agreement [Member] \| First and Second Regulatory Milestones [Member] \| Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	3,800,000			3,800,000
CyDex License Agreement [Member] \| Third and Fourth Clinical Development Milestones [Member] \| Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	1,300,000			1,300,000
CyDex License Agreement [Member] \| Third and Fourth Regulatory Milestones [Member] \| Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	8,500,000			8,500,000
CyDex License Agreement [Member] \| Clinical Development [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense	0		$ 300,000	0
Milestones achieved \| Milestone			1
Milestone payments	0			0
CyDex License Agreement [Member] \| Clinical Development [Member] \| Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	800,000			800,000
CyDex License Agreement [Member] \| Regulatory Milestones [Member] \| Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 1,800,000			$ 1,800,000

Commitments and Contingencies - Washington University License Agreement - Additional Information (Detail) - Washington University License Agreement [Member] - USD ($)	1 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended
	Nov. 30, 2013	Jun. 30, 2016	Jun. 30, 2016	Dec. 31, 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		$ 0	$ 0		$ 100,000
Milestone payments		$ 0	$ 0
Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense				$ 50,000
Milestone payments				$ 50,000
Maximum [Member] \| Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	500,000
Maximum [Member] \| Clinical Development [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 700,000

Commitments and Contingencies - University of California License Agreements - Additional Information (Detail) - University of California License Agreements [Member]	1 Months Ended	3 Months Ended			6 Months Ended		12 Months Ended
	May 31, 2014 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($) Milestone	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense		$ 0			$ 0
Milestone payments		$ 0			$ 0
Upfront payment						$ 50,000
Annual license maintenance fee							$ 15,000
After The Effective Date [Member]
Commitments And Contingencies [Line Items]
Licenses Expiration period, maximum	27 years
After The First Sale [Member]
Commitments And Contingencies [Line Items]
Licenses Expiration period, maximum	15 years
Clinical Development [Member]
Commitments And Contingencies [Line Items]
Milestones achieved \| Milestone				1
Research and development expense related to milestone expense			$ 25,000	$ 100,000
Milestone payments				$ 100,000
Clinical Development [Member] \| Maximum [Member]
Commitments And Contingencies [Line Items]
Milestone payments	$ 100,000
Percentage of net sales paid as royalties	1.00%
Regulatory Milestones [Member] \| Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments			700,000			700,000
Sales Milestones [Member] \| Maximum [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]	1 Months Ended			3 Months Ended			6 Months Ended
	Jun. 30, 2015 Milestone	Mar. 31, 2015 Milestone	Jan. 31, 2014 USD ($) shares	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($) shares	Mar. 31, 2015 USD ($) shares	Jun. 30, 2016 USD ($)
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense				$ 0			$ 0
Milestone payments				$ 0			$ 0
Clinical Development and Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Milestone payment			$ 2,000,000
Shares of common stock for attaining milestones \| shares			126,984
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 \| shares						7,936
Milestones achieved \| Milestone		1
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 \| shares					15,873
Milestones achieved \| Milestone	1

Sale of Equity Securities - Additional Information (Detail) $ / shares in Units, $ in Millions	Jan. 12, 2016 USD ($) $ / shares shares
Equity [Abstract]
Issuance of common stock, shares \| shares	3,157,894
Common stock price per share \| $ / shares	$ 47.50
Proceeds from public offering of common stock, net of commissions and underwriting discounts and estimated offering expenses \| $	$ 140.4

Stock-Based Compensation - Additional Information (Detail)		3 Months Ended			6 Months Ended		12 Months Ended
	Jan. 01, 2016 shares	Jun. 30, 2016 USD ($) shares	Sep. 30, 2015 Milestone	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2015	Jul. 02, 2014 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation granted under plan vest period					4 years
Share based compensation, vest period					1 year
Share based compensation, term of plan					10 years
Milestone expense \| $		$ 0			$ 0
Weighted average grant date fair value per share \| $ / shares					$ 22.23	$ 41.68
Share option, forfeiture rate					9.60%	10.00%
Stock-based compensation expense \| $		4,465,000		$ 5,398,000	$ 8,179,000	$ 6,747,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense \| $		4,000			$ 4,000
Weighted average period of unrecognized compensation costs					1 month 10 days
Stock-based compensation expense \| $		15,000		100,000	$ 31,000	$ 200,000
Issued, Shares-Restricted stock					0	0
Stock repurchased, shares					0	0
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option grant					969,785
Total unrecognized stock-based compensation expense \| $		39,600,000			$ 39,600,000
Weighted average period of unrecognized compensation costs					2 years 10 months 24 days
Total fair value of shares vested \| $					$ 9,700,000	$ 1,700,000
Intrinsic value of options exercised \| $					2,300,000	$ 19,900,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense \| $		$ 9,100,000			$ 9,100,000
Number of shares outstanding unvested stock options		433,015			433,015
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		4,959,683			4,959,683
Common stock available for issuance under 2014 Stock Option Plan		1,081,131			1,081,131
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]
Common stock available for issuance under 2014 Stock Option Plan	1,154,653
Percentage of increase on issued and outstanding shares of Common stock	4.00%
Percentage of performance based option grants that were achieved							35.00%
Milestones achieved \| Milestone			1
2014 Stock Option Plan [Member] \| Performance Milestone [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options with performance-based criteria					74,039	497,100
Stock-based compensation expense \| $				$ 3,400,000		$ 3,400,000
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock initially authorized for issuance under this plan								282,000
Number of shares issued under the plan					7,159

Stock-Based Compensation - Summary of Recognized Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 4,465	$ 5,398	$ 8,179	$ 6,747
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	2,037	2,298	3,649	2,821
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 2,428	$ 3,100	$ 4,530	$ 3,926

Stock-Based Compensation - Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected volatility	80.73%	88.58%	80.11%	92.44%
Risk free interest rate	1.42%	1.69%	1.41%	1.49%
Expected term	6 years 22 days	5 years 8 months 16 days	6 years 22 days	5 years 10 months 13 days

Stock-Based Compensation - Summary of Activity Relating to Stock Options (Detail) - Options to Purchase Common Stock [Member] - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Stock options	3,002,809
Granted, Stock options	969,785
Exercised, Stock options	(57,142)
Forfeited, Stock options	(36,900)
Ending balance, Outstanding Shares-Stock options	3,878,552	3,002,809
Vested and expected to vest, Stock options	3,168,000
Exercisable, Stock options	1,135,287
Beginning balance, Weighted Average Exercise Price-Stock options	$ 26.67
Granted, Weighted Average Exercise Price-Stock options	32.25
Exercised, Weighted Average Exercise Price-Stock options	1.47
Forfeited, Weighted Average Exercise Price-Stock options	56.07
Ending balance, Outstanding Weighted Average Exercise Price-Stock options	28.16	$ 26.67
Vested and expected to vest, Weighted Average Exercise Price-Stock options	26.93
Exercisable, Weighted Average Exercise Price-Stock options	$ 20.40
Outstanding, Weighted Average Remaining Life-Stock options	8 years 6 months 18 days	8 years 8 months 1 day
Vested and expected to vest, Weighted Average Remaining Life-Stock options	8 years 5 months 27 days
Exercisable, Weighted Average Remaining Life-Stock options	7 years 10 months 28 days
Outstanding, Aggregate Intrinsic Value-Stock options	$ 34,015	$ 96,479
Vested and expected to vest, Aggregate Intrinsic Value-Stock options	31,690
Exercisable, Aggregate Intrinsic Value-Stock options	$ 17,403

Stock-Based Compensation - Summary of Activity Relating to Restricted Stock (Detail) - Restricted Stock [Member] - shares	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, Shares at beginning balance-Restricted stock	42,781
Issued, Shares-Restricted stock	0	0
Vested, Shares-Restricted stock	(31,545)
Forfeited, Shares-Restricted stock	0
Repurchased, Shares-Restricted stock	0	0
Outstanding, Shares at ending balance-Restricted stock	11,236

Net Loss Per Share - Summary of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator:
Net loss	$ (34,747)	$ (25,027)	$ (65,290)	$ (41,898)
Denominator:
Weighted average common stock outstanding-basic	32,062,298	27,860,332	31,835,194	26,765,705
Dilutive effect of shares of common stock equivalents resulting from common stock options	0	0	0	0
Weighted average common stock outstanding-diluted	32,062,298	27,860,332	31,835,194	26,765,705
Net loss per share-basic and diluted	$ (1.08)	$ (0.90)	$ (2.05)	$ (1.57)

Net Loss Per Share - Summary of Common Stock Equivalents Outstanding (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	3,463,965	1,749,374	3,463,965	1,749,374
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	3,445,537	1,643,654	3,445,537	1,643,654
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	7,192	1,500	7,192	1,500
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	11,236	104,220	11,236	104,220