Syndax Pharmaceuticals (SNDX) 10-Q 7 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Aug. 06, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	SNDX
Entity Registrant Name	SYNDAX PHARMACEUTICALS INC
Entity Central Index Key	0001395937
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		27,136,794
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-37708
Entity Tax Identification Number	320162505
Entity Address, Address Line One	35 Gatehouse Drive, Building D, Floor 3
Entity Address, City or Town	Waltham
Entity Address, State or Province	Massachusetts
Entity Address, Postal Zip Code	02451
City Area Code	781
Local Phone Number	419-1400

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 26,666	$ 33,769
Restricted cash	101	101
Short-term investments	53,854	47,142
Prepaid expenses and other current assets	5,154	2,334
Total current assets	85,775	83,346
Property and equipment, net	327	373
Right-of-use asset, net	1,087
Other assets	201	219
Total assets	87,390	83,938
Current liabilities:
Accounts payable	2,276	1,439
Accrued expenses and other current liabilities	13,168	13,149
Current portion of deferred revenue	1,517	1,517
Current portion of right-of-use liability	530
Total current liabilities	17,491	16,105
Long-term liabilities:
Deferred revenue, less current portion	13,892	14,650
Right-of-use liability, less current portion	725
Other long-term liabilities	7	136
Total long-term liabilities	14,624	14,786
Total liabilities	32,115	30,891
Commitments
Stockholders’ equity:
Preferred stock, $0.001 par value, 10,000,000 shares authorized; 0 shares outstanding at June 30, 2019 and December 31, 2018
Common stock, $0.0001 par value, 100,000,000 shares authorized; 27,117,946 and 24,835,951 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively	3	2
Additional paid-in capital	523,855	492,493
Accumulated other comprehensive income (loss)	58	(25)
Accumulated deficit	(468,641)	(439,423)
Total stockholders’ equity	55,275	53,047
Total liabilities and stockholders’ equity	$ 87,390	$ 83,938

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	27,117,946	24,835,951
Common stock, shares outstanding	27,117,946	24,835,951

Condensed Consolidated Statemen

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue:
Total revenues	$ 379	$ 379	$ 758	$ 758
Type of revenue [extensible list]	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 12,290	$ 14,851	$ 23,569	$ 30,190
General and administrative	3,463	4,479	7,374	9,270
Total operating expenses	15,753	19,330	30,943	39,460
Loss from operations	(15,374)	(18,951)	(30,185)	(38,702)
Other income (expense):
Interest income, net	501	459	953	934
Other (expense) income	(43)	104	14	(17)
Total other income	458	563	967	917
Net loss	(14,916)	(18,388)	(29,218)	(37,785)
Other comprehensive income (loss):
Unrealized gain on marketable securities	50	129	83	54
Comprehensive loss	(14,866)	(18,259)	(29,135)	(37,731)
Net loss attributable to common stockholders	$ (14,916)	$ (18,388)	$ (29,218)	$ (37,785)
Net loss per share attributable to common stockholders—basic and diluted	$ (0.47)	$ (0.74)	$ (1)	$ (1.54)
Weighted-average number of common shares used to compute net loss per share attributable to common stockholders —basic and diluted	31,605,279	24,705,441	29,327,029	24,592,483

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (29,218)	$ (37,785)
Adjustments to reconcile net loss to net cash from operating activities:
Depreciation, amortization and accretion	(404)	(137)
Stock-based compensation	2,930	2,992
Other	(1)	(2)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(2,665)	(2,847)
Accounts payable	838	3,067
Deferred revenue	(758)	(758)
Accrued expenses and other liabilities	(78)	451
Net cash used in operating activities	(29,356)	(35,019)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment		(173)
Purchases of short-term investments	(59,894)	(34,149)
Proceeds from sales and maturities of short-term investments	53,715	66,250
Net cash (used in) provided by investing activities	(6,179)	31,928
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from stock option exercises	151	26
Proceeds from Employee Stock Purchase Plan	72	97
Other		(1)
Net cash provided by financing activities	28,432	122
NET DECREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(7,103)	(2,969)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH—beginning of period	33,985	35,389
CASH, CASH EQUIVALENTS AND RESTRICTED CASH —end of period	26,882	32,420
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Issuance costs included in accounts payable and accrued expenses		$ 32
At-the-Market Offering [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net	830
Private Placement [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net	$ 27,379

Nature of Business

Nature of Business	6 Months Ended
	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business	1. Nature of Business Syndax Pharmaceuticals, Inc. (“we,” “us,” “our” or the “Company”) is a clinical stage biopharmaceutical company developing an innovative pipeline of cancer therapies. We were incorporated in Delaware in 2005. We base our operations in Waltham, Massachusetts and we operate in one segment.

Basis of Presentation

Basis of Presentation	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	2. Basis of Presentation The Company has prepared the accompanying condensed consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. The interim unaudited condensed financial statements have been prepared on the same basis as the annual audited financial statements and in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of June 30, 2019, and the results of operations and comprehensive loss for the three and six months ended June 30, 2019 and 2018, and cash flows for the six months ended June 30, 2019 and 2018. The results for the six months ended June 30, 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019, any other interim periods, or any future year or period. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2018, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K that was filed with the Securities and Exchange Commission (“SEC”) on March 7, 2019. In 2011, the Company established a wholly owned subsidiary in the United Kingdom. There have been no activities for this entity to date. In 2014, the Company established a wholly owned U.S. subsidiary, Syndax Securities Corporation. The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	3. Summary of Significant Accounting Policies Significant Accounting Policies The Company’s significant accounting policies, which are disclosed in the audited consolidated financial statements for the year ended December 31, 2018 and the notes thereto are included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 7, 2019. Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of costs and expenses during the reporting period. The Company bases estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. The Company evaluates its estimates and assumptions on an ongoing basis. The Company’s actual results may differ from these estimates under different assumptions or conditions. Recently Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, Leases (Topic 842) (“ASU 2016-02”). The Company adopted ASU 2016-02 and its related amendments (collectively known as Accounting Standards Codification (“ASC”) 842) using the prospective method, effective on January 1, 2019. See Note 5 “Leases” for the required disclosures related to the impact of adopting this standard and a discussion of the Company’s updated policies related to leases. The Company adopted ASU 2016-02 on January 1, 2019, and it did not have a material impact on its condensed consolidated balance sheet, condensed consolidated statement of comprehensive loss or condensed consolidated statement of cash flows.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	6 Months Ended
	Jun. 30, 2019
Revenue From Contract With Customer [Abstract]
Revenue from Contracts with Customers	4. Revenue from Contracts with Customers On December 19, 2014 (the “Effective Date”), the Company entered into the KHK License Agreement, under which the Company granted KHK an exclusive license to develop and commercialize entinostat in Japan and Korea. Under the terms of the KHK License Agreement, the Company will be responsible for the manufacture and supply of the products during the development activities. In addition to the license and manufacturing obligations, the Company is obligated to provide KHK access to know-how and regulatory information the Company may develop over the life of the entinostat patent. Lastly, to the extent additional intellectual property is developed during the term of the agreement, KHK will receive the right to the intellectual property when and if available. KHK will conduct the development, regulatory approval filings, and commercialization activities of entinostat in Japan and Korea. KHK paid the Company $25.0 million upfront, which included a $7.5 million equity investment and a $17.5 million non-refundable cash payment. In addition, to the extent certain development and commercial milestones are achieved, KHK will be required to pay the Company up to $75.0 million in milestone payments over the term of the license agreement. The term of the agreement commenced on the Effective Date and, unless earlier terminated in accordance with the terms of the agreement, will continue on a country-by-country and product-by-product basis, until the later of: (i) the date all valid claims of the last effective patent among the Company’s patents expires or is abandoned, withheld, or is otherwise invalidated in such country; and (ii) 15 years from the date of the first commercial sale of a product in the Japan or Korea. The equity purchase and the up-front payment of the license fee were accounted for separately. The Company allocated the amount of consideration equal to the fair value of the shares on the Effective Date, which resulted in $7.7 million of proceeds allocated to the equity purchase and the remaining consideration of $17.3 million allocated to the up-front license fee. In October 2017, the Company announced that KHK enrolled the first Japanese patient into a local pivotal study of entinostat for the treatment of hormone receptor positive, human epidermal growth factor receptor 2 negative breast cancer. In accordance with the terms of the license agreement, KHK paid the Company a $5.0 million milestone payment which the Company received in December 2017. In October 2016, the Company entered into a clinical trial co-funding agreement with KHK under which the Company expanded its clinical trial agreement with Eastern Cooperative Oncology Group (the “ECOG Agreement”) to include enrollments from sites in Korea. The Company determined that the performance obligations associated with the KHK License Agreement include (i) the combined license, rights to access and use materials and data, and rights to additional intellectual property, and (ii) the clinical supply obligation. All other goods or services promised to KHK are immaterial in the context of the agreement. Under ASC 606, the identification of the clinical supply obligation as a distinct performance obligation separate and apart from the license performance obligation resulted in a change in the performance period. The start of the performance period under ASC 606 was determined to be the contract inception date, December 19, 2014. The clinical supply was identified as a separate performance obligation under ASC 606 as (i) the Company is not providing a significant service of integration whereby the clinical supply and other promises are inputs into a combined output, (ii) the clinical supply does not significantly modify or customize the other promises nor is it significantly modified or customized by them, and (iii) the clinical supply is not highly interdependent or highly interrelated with the other promises in the agreement as KHK could choose not to purchase the clinical supply from the Company without significantly affecting the other promised goods or services. The Company further concluded that the clinical supply represented an immaterial performance obligation and therefore the entire $17.3 million allocated to the upfront payment was allocated to the combined license and will be recognized ratably over the performance period, representing contract inception though 2029. In 2017, KHK achieved a development milestone, and was required to pay the Company $5.0 million. The Company is recognizing the development milestone consideration over the performance period coinciding with the license to intellectual property. As the Company determined that its performance obligations associated with the KHK Agreement at contract inception were not distinct and represented a single performance obligation, and that the obligations for goods and services provided would be completed over the performance period of the agreement, any payments received by the Company from KHK, including the upfront payment and progress-dependent development and regulatory milestone payments, are recognized as revenue using a time-based proportional performance model over the contract term (December 2014 through 2029) of the collaboration, within license fees. Contract liabilities consisted of deferred revenue, as presented on the consolidated balance sheet, as of June 30, 2019. Deferred revenue related to the KHK License Agreement was $15.4 million as of June 30, 2019 and will be recognized over the remainder of the contract term.

Leases

Leases	6 Months Ended
	Jun. 30, 2019
Lessee Disclosure [Abstract]
Leases	5. Leases Adoption of ASC Topic 842, “Leases” The Company adopted ASC 842 on January 1, 2019, using the prospective approach which provides a method for recording existing leases at adoption using the effective date of the standard as its initial application date. ASC 842 generally requires all leases to be recognized on the balance sheet. In addition, the Company elected the relief package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed the Company not to reassess whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases and initial direct costs for any existing leases. The reported results for 2019 reflect the application of ASC 842 guidance while the reported results for 2018 were prepared under the guidance of ASC 840, Leases. The adoption of ASC 842 resulted in the recording of an additional lease asset and lease liability of approximately $1.3 million as of January 1, 2019. ASC 842 did not materially impact the Company’s condensed consolidated results of operations, equity or cash flows as of the adoption date or for the periods presented. Leases The Company determines whether an arrangement is a lease at inception. Operating lease right-of-use (“ROU”) assets and lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. Lease agreements with lease and non-lease components are accounted for separately. For leases that do not provide an implicit rate, the Company uses the incremental borrowing rate based on the information available at commencement date in determining the present value of future payments. The ROU asset also includes any lease payments made and excludes lease incentives and initial direct costs incurred. The lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Leases with an initial term of 12 months or less are not recorded on the balance sheet as the Company has elected to apply the short-term lease exemption. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. The Company identified two existing long-term building leases on the adoption date of ASC 842 that are classified as operating leases. In September 2016, the Company entered into a five-year operating lease for 12,207 square feet of office space in Waltham, Massachusetts, with a lease commencement date of March 1, 2017. In December 2015, the Company entered into a 62-month operating lease for 4,039 square feet of space in New York, New York, which commenced on January 1, 2016. The remaining lease terms as of June 30, 2019 for the facility in Waltham, Massachusetts and New York, New York, were 32 and 20 months, respectively. As of June 30, 2019, the condensed consolidated balance sheet includes a $1.1 million operating lease ROU asset and a $1.3 million ROU liability. The Company used a weighted average discount rate of 14% to calculate its lease obligations, and an increase or decrease in the rate does not have a significant impact on the ROU asset or ROU liability. The ROU asset is amortized on a straight-line basis over the remainder of the lease term. For the six months ended June 30, 2019, the Company recorded approximately $243,000 in operating lease expense and made approximately $282,000 in lease payments. Future minimum lease payments under the Company’s operating leases as of June 30, 2019 and December 31, 2018, were as follows: Maturity of lease liabilities As of As of (in thousands) June 30, 2019 December 31, 2018 2019 $ 285 $ 569 2020 585 588 2021 394 395 2022 59 59 Thereafter — — Total lease payments $ 1,323 $ 1,611 Less: imputed interest (68 ) Total operating lease liability $ 1,255 Future minimum lease payments under the Company’s capital leases as of June 30, 2019 and December 31, 2018, were $11,000 and $10,000, respectively.

Net Loss per Share Attributable

Net Loss per Share Attributable to Common Stockholders	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Net Loss per Share Attributable to Common Stockholders	6. Net Loss per Share Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period. Because the Company has reported a net loss for all periods presented, diluted net loss per common share is the same as basic net loss per common share for those periods. The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (In thousands, except share and per share data) (In thousands, except share and per share data) Numerator—basic and diluted: Net loss $ (14,916 ) $ (18,388 ) $ (29,218 ) $ (37,785 ) Net loss attributable to common stockholders—basic and diluted $ (14,916 ) $ (18,388 ) $ (29,218 ) $ (37,785 ) Net loss per share attributable to common stockholders—basic and diluted $ (0.47 ) $ (0.74 ) $ (1.00 ) $ (1.54 ) Denominator—basic and diluted: Weighted-average number of common shares used to compute net loss per share attributable to common stockholders—basic and diluted 31,605,279 24,705,441 29,327,029 24,592,483 The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares outstanding because such securities have an antidilutive impact due to losses reported (in common stock equivalent shares): June 30, 2019 2018 Options to purchase common stock 5,770,616 4,232,590 Warrants to purchase common stock 4,595,039 — Employee Stock Purchase Plan 18,848 15,804 In June 2018, the Company signed an exchange agreement with an investor under which the investor exchanged 2,000,000 shares of common stock for 2,000,000 warrant shares. The warrants are exercisable into shares of common stock for $0.0001 per share. The shares of common stock into which the warrants may be exercised are considered outstanding for the purposes of computing earnings per share. In March 2019, the Company sold 2,095,039 shares of common stock as well as 2,500,000 pre-funded warrant shares (see Note 13). The warrants are exercisable into shares of common stock for $0.0001 per share. The shares of common stock into which the warrants may be exercised are considered outstanding for the purposes of computing earnings per share.

Significant Agreements

Significant Agreements	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Significant Agreements	7. Significant Agreements Vitae Pharmaceuticals, Inc. In October 2017, the Company entered into a license agreement (the “Allergan License Agreement”) with Vitae Pharmaceuticals, Inc., a subsidiary of Allergan plc (“Allergan”), under which Allergan granted the Company an exclusive, sublicensable, worldwide license to a portfolio of preclinical, orally available, small molecule inhibitors of the interaction of Menin with the Mixed Lineage Leukemia (“MLL”) protein (the “Menin Assets”). The Company made a nonrefundable upfront payment of $5.0 million to Allergan in the fourth quarter of 2017. Additionally, subject to the achievement of certain milestone events, the Company may be required to pay Allergan up to $99.0 million in one-time development and regulatory milestone payments over the term of the Allergan License Agreement. In the event that the Company or any of its affiliates or sublicensees commercializes the Menin Assets, the Company will also be obligated to pay Allergan low single to low double-digit royalties on sales, subject to reduction in certain circumstances, as well as up to an aggregate of $70.0 million in potential one-time, sales-based milestone payments based on achievement of certain annual sales thresholds. Under certain circumstances, the Company may be required to share a percentage of non-royalty income from sublicensees, subject to certain deductions, with Allergan. The Company is solely responsible for the development and commercialization of the Menin Assets. Each party may terminate the Allergan License Agreement for the other party’s uncured material breach or insolvency; and the Company may terminate the Allergan License Agreement at will at any time upon advance written notice to Allergan. Allergan may terminate the Allergan License Agreement if the Company or any of its affiliates or sublicensees institutes a legal challenge to the validity, enforceability, or patentability of the licensed patent rights. Unless terminated earlier in accordance with its terms, the Allergan License Agreement will continue on a country-by-country and product-by-product basis until the later of: (i) the expiration of all of the licensed patent rights in such country; (ii) the expiration of all regulatory exclusivity applicable to the product in such country; and (iii) 10 years from the date of the first commercial sale of the product in such country. As of the date of the Allergan License Agreement, the asset acquired had no alternative future use nor had it reached a stage of technological feasibility. As the processes or activities that were acquired along with the license do not constitute a “business,” the transaction has been accounted for as an asset acquisition. In June 2019, the Company achieved certain development and regulatory milestones. As a result, in June 2019, the Company recorded $4.0 million as research and development expense and has recorded the amount payable in accrued milestone expenses as of June 30, 2019. UCB Biopharma Sprl In 2016, the Company entered into a license agreement (the “UCB License Agreement”) with UCB Biopharma Sprl (“UCB”), under which UCB granted to the Company a worldwide, sublicenseable, exclusive license to UCB6352, which the Company refers to as SNDX-6352, an investigational new drug (“IND”) ready anti-CSF-1R monoclonal antibody. The Company made a nonrefundable upfront payment of $5.0 million to UCB in 2016. Additionally, subject to the achievement of certain milestone events, the Company may be required to pay UCB up to $119.5 million in one-time development and regulatory milestone payments over the term of the UCB License Agreement. In the event that the Company or any of its affiliates or sublicensees commercializes SNDX-6352, the Company will also be obligated to pay UCB low double-digit royalties on sales, subject to reduction in certain circumstances, as well as up to an aggregate of $250.0 million in potential one-time, sales-based milestone payments based on achievement of certain annual sales thresholds. Under certain circumstances, the Company may be required to share a percentage of non-royalty income from sublicensees, subject to certain deductions, with UCB. The Company is solely responsible for the development and commercialization of SNDX-6352, except that UCB is performing a limited set of transitional chemistry, manufacturing and control tasks related to SNDX-6352. Each party may terminate the UCB License Agreement for the other party’s uncured material breach or insolvency; and the Company may terminate the UCB License Agreement at will at any time upon advance written notice to UCB. UCB may terminate the UCB License Agreement if the Company or any of its affiliates or sublicensees institutes a legal challenge to the validity, enforceability, or patentability of the licensed patent rights. Unless terminated earlier in accordance with its terms, the UCB License Agreement will continue on a country-by-country and product-by-product basis until the later of: (i) the expiration of all of the licensed patent rights in such country; (ii) the expiration of all regulatory exclusivity applicable to the product in such country; and (iii) 10 years from the date of the first commercial sale of the product in such country. As of the date of the UCB License Agreement, the asset acquired had no alternative future use nor had it reached a stage of technological feasibility. As the processes or activities that were acquired along with the license do not constitute a “business,” the transaction has been accounted for as an asset acquisition. As a result, in 2016, the upfront payment of $5.0 million was recorded as research and development expense. Eastern Cooperative Oncology Group In March 2014, the Company entered into the ECOG Agreement with Eastern Cooperative Oncology Group, a contracting entity for the Eastern Cooperative Oncology Group—American College of Radiology Imaging Network Cancer Research Group (“ECOG-ACRIN”), that describes the parties’ obligations with respect to the NCI-sponsored pivotal Phase 3 clinical trial of entinostat. Under the terms of the ECOG Agreement, ECOG-ACRIN will perform this clinical trial in accordance with the clinical trial protocol and a mutually agreed scope of work. The Company is providing a fixed level of financial support for the clinical trial through an upfront payment of $0.7 million and a series of payments of up to $1.0 million each that are comprised of milestone payments through the completion of enrollment and time-based payments through the completion of patient monitoring post-enrollment. In addition, the Company is obligated to supply entinostat and placebo to ECOG-ACRIN for use in the clinical trial. During the second quarter of 2016, the ECOG Agreement was amended to provide additional study activities and the contractual obligation increased by $0.8 million. During the first quarter of 2017, the ECOG Agreement was amended to expand the study to include enrollments from sites in Korea and to provide additional study activities and the contractual obligation increased by $2.0 million. As of June 30, 2019, the Company’s aggregate payment obligations under this agreement were approximately $24.5 million and its remaining payment obligations are approximately $8.3 million over an estimated period of approximately three years. Data and inventions from the Phase 3 clinical trial are owned by ECOG-ACRIN. The Company has access to the data generated in the clinical trial, both directly from ECOG-ACRIN under the ECOG Agreement as well as from the NCI. Additionally, ECOG-ACRIN has granted the Company a non-exclusive royalty-free license to any inventions or discoveries that are derived from entinostat as a result of its use during the clinical trial, along with a first right to negotiate an exclusive license to any of these inventions or discoveries. Either party may terminate the ECOG Agreement in the event of an uncured material breach by the other party or if the U.S. Food and Drug Administration (“FDA”) or National Cancer Institute (“NCI”) withdraws the authorization to perform the clinical trial in the United States. The parties may jointly terminate the ECOG Agreement if the parties agree that safety-related issues support termination of the clinical trial. The Company records the appropriate clinical trial expenses in its financial statements by matching those expenses with the period in which the services and efforts are expended. The Company accounts for these expenses according to the progress of the clinical trial as measured by patient enrollment and the timing of various aspects of the clinical trial. The Company determines accrual estimates through financial models, taking into account discussion with applicable personnel and ECOG-ACRIN as to the progress or state of consummation of the clinical trial or the services completed. Bayer Pharma AG (formerly known as Bayer Schering Pharma AG) In March 2007, the Company entered into a license agreement (the “Bayer Agreement”) with Bayer Schering Pharma AG (“Bayer”) for a worldwide, exclusive license to develop and commercialize entinostat and any other products containing the same active ingredient. Under the terms of the Bayer Agreement, the Company paid a nonrefundable upfront license fee of $2.0 million and is responsible for the development and marketing of entinostat. The Company recorded the $2.0 million license fee as research and development expense during the year ended December 31, 2007, as it had no alternative future use. The Company will pay Bayer royalties on a sliding scale based on net sales, if any, and make future milestone payments to Bayer of up to $150.0 million in the event that certain specified development and regulatory goals and sales levels are achieved. In June 2014, a development milestone was achieved, and the Company recorded $2.0 million of research and development expense, which has been fully paid. In connection with the Bayer Agreement, the Company issued to Bayer a warrant to purchase the number of shares of the Company’s common stock equal to 1.75% of the shares of common stock outstanding on a fully diluted basis as of the earlier of the date the warrant was exercised or the closing of the IPO. The warrant contained anti-dilution protection to maintain Bayer’s potential ownership at 1.75% of the shares of common stock outstanding on a fully diluted basis, requiring that the actual number of shares of common stock issuable pursuant to the warrant be increased or decreased for any changes in the fully diluted shares of common stock outstanding. The warrant was exercisable at an exercise price of $1.54 per share and would have expired upon the earlier of the 10-year anniversary of the closing of the IPO or the date of the consummation of a disposition transaction. The warrant was classified as a long-term liability and recorded at fair value with the changes in the fair value recorded in other expense. The Company used the Black-Scholes option-pricing model to determine the fair value of the warrant. Upon the closing of the IPO, the anti-dilution protection for the warrant expired, resulting in the reclassification of the warrant liability to additional paid-in capital. The warrant was re-measured using current assumptions just prior to the reclassification. On March 1, 2018, Bayer notified the Company of its election to exercise the warrant utilizing the net exercise feature contained therein, resulting in the Company’s issuance to Bayer of 299,215 shares of the Company’s common stock for no net cash proceeds.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	8. Fair Value Measurements The carrying amounts of cash and cash equivalents, restricted cash, accounts payable, and accrued expenses approximated their estimated fair values due to the short-term nature of these financial instruments. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value are performed in a manner to maximize the use of observable inputs and minimize the use of unobservable inputs. The accounting standard describes a fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value, which are the following: Level 1— Quoted prices (unadjusted) in active markets that are accessible at the market date for identical unrestricted assets or liabilities. Level 2— Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs for which all significant inputs are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3— Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. During the periods presented, the Company has not changed the manner in which it values assets and liabilities that are measured at fair value using Level 3 inputs. The Company recognizes transfers between levels of the fair value hierarchy as of the end of the reporting period. There were no transfers within the hierarchy for any of periods presented. A summary of the assets and liabilities carried at fair value in accordance with the hierarchy defined above is as follows: Fair Value Measurements Using Quoted Prices Significant (unadjusted) Other Significant Total in Active Observable Unobservable Carrying Markets Inputs Inputs Value (Level 1) (Level 2) (Level 3) (In thousands) June 30, 2019 Assets: Cash and cash equivalents $ 26,666 $ 26,666 $ — $ — Short-term investments 53,854 — 53,854 — Total assets $ 80,520 $ 26,666 $ 53,854 $ — December 31, 2018 Assets: Cash and cash equivalents $ 33,769 $ 29,270 $ 4,499 $ — Short-term investments 47,142 — 47,142 — Total assets $ 80,911 $ 29,270 $ 51,641 $ — Cash of $26.7 million and $29.3 million as of June 30, 2019 and December 31, 2018, respectively, consisted of overnight investments and money market funds and are classified within Level 1 of the fair value hierarchy because they are valued using quoted market prices in active markets. Cash equivalents of $4.5 million as of December 31, 2018, consisted of highly rated corporate bonds and commercial paper and are classified within Level 2 of the fair value hierarchy because pricing inputs are other than quoted prices in active markets, which are either directly or indirectly observable as of the reporting date, and fair value is determined through the use of models or other valuation methodologies. Short-term investments of $53.9 million and $47.1 million as of June 30, 2019 and December 31, 2018, respectively, consisted of commercial paper, highly rated corporate bonds and asset backed securities and are classified within Level 2 of the fair value hierarchy because pricing inputs are other than quoted prices in active markets, which are either directly or indirectly observable as of the reporting date, and fair value is determined through the use of models or other valuation methodologies. The short-term investments are classified as available-for-sale securities. As of June 30, 2019, the remaining contractual maturities of the available-for-sale securities were less than one year, and the balance in the Company’s accumulated other comprehensive income was comprised solely of activity related to the Company’s available-for-sale securities. There were no realized gains or losses recognized on the sale or maturity of available-for-sale securities during the three months ended June 30, 2019 and 2018. As a result, the Company did not reclassify any amounts out of accumulated other comprehensive income for the same periods. The Company has a limited number of available-for-sale securities in insignificant loss positions as of June 30, 2019, which the Company does not intend to sell and has concluded it will not be required to sell before recovery of the amortized cost for the investment at maturity. The following table summarizes the available-for-sale securities: Amortized Unrealized Unrealized Cost Gains Losses Fair Value (In thousands) June 30, 2019 Commercial paper $ 31,213 $ 44 $ — $ 31,257 Corporate bonds 22,085 13 — $ 22,098 Asset back securities 498 1 — $ 499 $ 53,796 $ 58 $ — $ 53,854 December 31, 2018 Commercial paper $ 22,619 $ — $ (15 ) $ 22,604 Corporate bonds 29,047 2 (12 ) 29,037 $ 51,666 $ 2 $ (27 ) $ 51,641

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	6 Months Ended
	Jun. 30, 2019
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	9. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following: June 30, 2019 December 31, 2018 (In thousands) Short-term deposits $ 3,147 $ 663 Prepaid clinical supplies 213 101 Interest receivable on investments 208 253 Reimbursable costs 677 797 Prepaid insurance 582 188 Other 327 332 Total prepaid expenses and other current assets $ 5,154 $ 2,334

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	6 Months Ended
	Jun. 30, 2019
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	10. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: June 30, 2019 December 31, 2018 (In thousands) Accrued professional fees $ 425 $ 484 Accrued compensation and related costs 1,774 2,804 Accrued clinical costs 6,700 9,726 Accrued milestones 4,000 — Other 269 135 Total accrued expenses and other current liabilities $ 13,168 $ 13,149

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	11. Stock-Based Compensation In January 2019, the number of shares of common stock available for issuance under the 2015 Omnibus Incentive Plan (“2015 Plan”), was increased by 993,438 shares due to the automatic annual provision to increase shares available under the 2015 Plan. As of June 30, 2019, the total number of shares of common stock available for issuance under the 2015 Plan was 876,639. The Company recognized stock-based compensation expense related to the issuance of stock option awards to employees and non-employees and related to the 2015 Employee Stock Purchase Plan (“ESPP”) in the condensed consolidated statements of comprehensive loss as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (In thousands) (In thousands) Research and development $ 537 $ 516 $ 1,071 $ 968 General and administrative 801 1,054 1,859 2,024 Total $ 1,338 $ 1,570 $ 2,930 $ 2,992 Compensation expense by type of award in the three and six months ended June 30, 2019 and 2018 was as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (In thousands) (In thousands) Stock options $ 1,308 $ 1,540 $ 2,867 $ 2,934 Employee Stock Purchase Plan 30 30 63 58 Total $ 1,338 $ 1,570 $ 2,930 $ 2,992 During the six months ended June 30, 2019, the Company granted 1,022,825 stock options to certain executives and employees having service-based vesting conditions. The grant date fair value of the options granted in the six months ended June 30, 2019, was $4.6 million, or $4.47 per share on a weighted-average basis, and will be recognized as compensation expense over the requisite service period of one to four years. During the six months ended June 30, 2019, the Company granted 583,000 stock options to certain employees to purchase shares of common stock that contain certain performance-based vesting criteria, primarily related to the 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, which consider the inherent risk and uncertainty regarding the future outcomes of the milestones. The achievement of one of the performance milestones was considered to be probable and the Company recorded approximately $80,000 of stock compensation expense associated with these awards for the six months ended June 30, 2019. For the remaining awards containing performance-based vesting criteria, the achievement of the milestones were considered not probable, nor met, and therefore no expense has been recognized related to these awards for the six months ended June 30, 2019. There were As of June 30, 2019, there was $11.2 million of unrecognized compensation cost related to employee and non-employee unvested stock options granted under the 2015 and 2007 Plans, which is expected to be recognized over a weighted-average remaining service period of 2.4 years. Stock compensation costs have not been capitalized by the Company.

Employee Stock Purchase Plan

Employee Stock Purchase Plan	6 Months Ended
	Jun. 30, 2019
Postemployment Benefits [Abstract]
Employee Stock Purchase Plan	12. Employee Stock Purchase Plan In January 2019, the number of shares of common stock available for issuance under the ESPP, was increased by 248,359 shares as a result of the automatic increase provision of the ESPP. As of June 30, 2019, the total number of shares of common stock available for issuance under the ESPP was 875,842. The issued 23,970 shares during the six months end June 30, 2019. The ESPP is considered a compensatory plan with the related compensation cost expensed over the six-month offering period starting on February 1 and on August 1. The compensation expense related to the ESPP for the three and six months ended June 30, 2019, was approximately $30,000 and $63,000, respectively. The compensation expense related to the ESPP recorded in the three and six months ended June 30, 2018, was approximately $30,000 and $58,000, respectively.

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Stockholders' Equity	13. Stockholders’ Equity The following table presents the changes in stockholders’ equity for the three and six months ended June 30, 2019: (In thousands, except share data) Common Stock $0.0001 Par Value Additional Paid-In Capital Accumulated Other Comprehensive Income / (Loss) Accumulated Deficit Total Stockholders’ Equity Shares Amount Balance as of January 1, 2019 24,835,951 $ 2 $ 492,493 $ (25 ) $ (439,423 ) $ 53,047 Stock purchase under ESPP 23,970 — — — — — Proceeds from 'at-the-market' offering, net of $34 offering expenses 140,819 — 830 — — 830 Stock-based compensation expense — — 1,592 — — 1,592 Proceeds from direct offering, net of $1,571 in common stock warrants, $78 offering expenses 2,095,039 1 10,921 — — 10,922 Proceeds from pre-funded common stock warrant from direct offering, net of $1,875 in common stock warrants, $93 offering expenses — — 13,032 — — 13,032 Issuance of common stock warrant with direct offering — — 3,446 — — 3,446 Unrealized gains on short-term investments — — — 33 — 33 Employee withholdings ESPP — — 26 — — 26 Net loss — — — — (14,302 ) (14,302 ) Balance as of March 31, 2019 27,095,779 $ 3 $ 522,340 $ 8 $ (453,725 ) $ 68,626 Stock-based compensation expense — — 1,338 — — 1,338 Offering expenses associated with direct offering — — (20 ) — — (20 ) Unrealized gains on short-term investments — — — 50 — 50 Employee withholdings ESPP — — 46 — — 46 Proceeds from exercise of stock options 22,167 — 151 — — 151 Net loss — — — — (14,916 ) (14,916 ) Balance as of June 30, 2019 27,117,946 $ 3 $ 523,855 $ 58 $ (468,641 ) $ 55,275 The following table represents the changes in stockholders’ equity for the three and six months ended June 30, 2018: (In thousands, except share data) Common Stock $0.0001 Par Value Additional Paid-In Capital Accumulated Other Comprehensive Income / (Loss) Accumulated Deficit Total Stockholders’ Equity Shares Amount Balance as of January 1, 2018 24,390,033 $ 2 $ 470,571 $ (143 ) $ (366,111 ) $ 104,319 Stock purchase under ESPP 8,696 — — — — — Stock-based compensation expense — — 1,421 — — 1,421 Stock issuance due to warrant exercise, cashless 299,215 — — — — — Unrealized gains on short-term investments — — — (75 ) — (75 ) Employee withholdings ESPP — — 34 — — 34 Cumulative effect adjustment of adoption ASU 2014-09 — — — — 649 649 Net loss — — — — (19,398 ) (19,398 ) Balance as of March 31, 2018 24,697,944 $ 2 $ 472,026 $ (218 ) $ (384,860 ) $ 86,951 Stock-based compensation expense — — 1,571 — — 1,571 Proceeds from exercise of stock options 7,850 — 26 — — 26 Unrealized gains on short-term investments — — — 129 — 129 Employee withholdings ESPP — — 63 — — 63 Retirement of common stock in exchange for common stock warrant 1 (2,000,000 ) — (16,780 ) — — (16,780 ) Issuance of common stock warrant in exchange for retirement of common stock 1 — — 16,780 — — 16,780 Net loss — — — — (18,388 ) (18,388 ) Balance as of June 30, 2018 22,705,794 $ 2 $ 473,686 $ (89 ) $ (403,247 ) $ 70,352 1 On June 18, 2018, the Company signed an exchange agreement with Biotechnology Value Fund and certain affiliated funds (“BVF”) under which BVF exchanged 2,000,000 shares of common stock for 2,000,000 warrant shares. The Company recorded the issuance of the warrant shares and the retirement of the common stock at fair value within additional paid-in capital. BVF can exercise the warrant shares at an exercise price per share equal to $0.0001 per share and the warrant shares expire 20 years from issuance. Per the terms of the warrant agreement, the outstanding warrants to purchase shares of common stock may not be exercised if the holder's ownership of the Company's common stock would exceed 9.99 percent following such exercise. In April 2017, the Company entered into a sales agreement with Cowen and Company, LLC (“Cowen”) under which the Company may issue and sell shares of our common stock having aggregate sales proceeds of up to $50.0 million from time to time through Cowen, acting as agent, in a series of one or more at-the-market (“ATM”) equity offerings. Cowen is not required to sell any specific amount, but acts as our sales agent using commercially reasonable efforts consistent with its normal trading and sales practices. The Company pays Cowen up to 3% of the gross proceeds from any common stock sold through this sales agreement. In the first quarter of 2019, the Company sold 140,819 shares of common stock under the ATM program for net proceeds of $0.8 million. In the second and third quarter of 2019, through August 6, 2019, the Company sold no additional shares of common stock under the ATM program. In March 2019, the Company issued 2,095,039 shares of its common stock and pre-funded warrants to purchase 2,500,000 shares of common stock (the “Pre-Funded Warrants”) to certain investors in a registered direct offering. The Pre-Funded Warrants are exercisable immediately upon issuance at an exercise price of $0.0001 per share and have a term of 20 years. The Company sold the shares of common stock and Pre-Funded Warrants together with two series of warrants, Series 1 Warrants and Series 2 Warrants, to purchase an aggregate of 4,595,039 shares of the Company’s common stock (the “Series Warrants”). The offering price for the securities was $6.00 per share (or $5.9999 for each Pre-Funded Warrant). The aggregate gross proceeds to the Company from this offering were $27.6 million, excluding any proceeds the Company may receive upon exercise of the Pre-Funded Warrants and Series Warrants and offering costs of $0.2 million. No underwriter or placement agent participated in the offering. The Series Warrants are immediately exercisable. Each Series 1 Warrant has an initial exercise price of $12.00 per share of common stock and each Series 2 Warrant has an initial exercise price of $18.00 per share of common stock, in each case subject to certain adjustments. The Series Warrants expire on the earlier of (i) 90 days following the Company’s confirmation to holders of the Company’s release of positive data confirming the achievement of the specified primary endpoint of overall survival benefit in the E2112 clinical trial in breast cancer patients, or (ii) December 31, 2020. If, prior to the expiration date of the Series Warrant, the Company sells additional capital stock or derivative securities convertible into or exercisable for capital stock, as defined, in one or more related transactions primarily for the purpose of raising capital at a Weighted-Average Price (as described below) below $12.00 per share, then the initial exercise price of the Series Warrants will be automatically reset upon exercise to an exercise price (the “Adjusted Exercise Price”) that is the midpoint between the initial exercise price and the lowest Weighted-Average Price per share at which the Company sells capital stock or derivative securities convertible into or exercisable for capital stock in a subsequent offering prior to the exercise date; provided, however, that the Adjusted Exercise Price will not be reduced below $6.00 per share. The Weighted-Average Price shall be calculated as the weighted-average common stock equivalent price of the equity securities sold in such transaction(s) (excluding any derivative securities with an exercise or conversion price that is above the closing sale price as of the time of pricing such offering(s)). In no event will the exercise price for the Series Warrants be adjusted more than once pursuant to this adjustment mechanism. The Series Warrants were classified as a component of permanent equity and were recorded at the issuance date using a relative fair value allocation method. The Series Warrants are equity classified because they are freestanding financial instruments that are legally detachable and separately exercisable from the equity instruments, are immediately exercisable, do not embody an obligation for the Company to repurchase its shares, and permits the holders to receive a fixed number of common shares upon exercise. In addition, such warrants do not provide any guarantee of value or return .

Related-Party Transactions

Related-Party Transactions	6 Months Ended
	Jun. 30, 2019
Related Party Transactions [Abstract]
Related-Party Transactions	14. Related-Party Transactions The Company’s chief executive officer and member of the board of directors is also a managing director at MPM Asset Management, LLC, which holds an investment in the Company’s common stock.

Basis of Presentation (Policies

Basis of Presentation (Policies)	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Principles of Consolidation	In 2011, the Company established a wholly owned subsidiary in the United Kingdom. There have been no activities for this entity to date. In 2014, the Company established a wholly owned U.S. subsidiary, Syndax Securities Corporation. The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Significant Accounting Policies	Significant Accounting Policies The Company’s significant accounting policies, which are disclosed in the audited consolidated financial statements for the year ended December 31, 2018 and the notes thereto are included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 7, 2019.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of costs and expenses during the reporting period. The Company bases estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. The Company evaluates its estimates and assumptions on an ongoing basis. The Company’s actual results may differ from these estimates under different assumptions or conditions.
Recently Issued and Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, Leases (Topic 842) (“ASU 2016-02”). The Company adopted ASU 2016-02 and its related amendments (collectively known as Accounting Standards Codification (“ASC”) 842) using the prospective method, effective on January 1, 2019. See Note 5 “Leases” for the required disclosures related to the impact of adopting this standard and a discussion of the Company’s updated policies related to leases. The Company adopted ASU 2016-02 on January 1, 2019, and it did not have a material impact on its condensed consolidated balance sheet, condensed consolidated statement of comprehensive loss or condensed consolidated statement of cash flows.

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2019
Lessee Disclosure [Abstract]
Summary of Future Minimum Lease Payments under Operating Leases	Future minimum lease payments under the Company’s operating leases as of June 30, 2019 and December 31, 2018, were as follows: Maturity of lease liabilities As of As of (in thousands) June 30, 2019 December 31, 2018 2019 $ 285 $ 569 2020 585 588 2021 394 395 2022 59 59 Thereafter — — Total lease payments $ 1,323 $ 1,611 Less: imputed interest (68 ) Total operating lease liability $ 1,255

Net Loss per Share Attributab_2

Net Loss per Share Attributable to Common Stockholders (Tables)	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (In thousands, except share and per share data) (In thousands, except share and per share data) Numerator—basic and diluted: Net loss $ (14,916 ) $ (18,388 ) $ (29,218 ) $ (37,785 ) Net loss attributable to common stockholders—basic and diluted $ (14,916 ) $ (18,388 ) $ (29,218 ) $ (37,785 ) Net loss per share attributable to common stockholders—basic and diluted $ (0.47 ) $ (0.74 ) $ (1.00 ) $ (1.54 ) Denominator—basic and diluted: Weighted-average number of common shares used to compute net loss per share attributable to common stockholders—basic and diluted 31,605,279 24,705,441 29,327,029 24,592,483
Potential Dilutive Securities Excluded from Computation of Diluted Net Loss per Common Share	The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares outstanding because such securities have an antidilutive impact due to losses reported (in common stock equivalent shares): June 30, 2019 2018 Options to purchase common stock 5,770,616 4,232,590 Warrants to purchase common stock 4,595,039 — Employee Stock Purchase Plan 18,848 15,804

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Schedule of Fair Values of Financial Assets and Liabilities Measured at Fair Value	A summary of the assets and liabilities carried at fair value in accordance with the hierarchy defined above is as follows: Fair Value Measurements Using Quoted Prices Significant (unadjusted) Other Significant Total in Active Observable Unobservable Carrying Markets Inputs Inputs Value (Level 1) (Level 2) (Level 3) (In thousands) June 30, 2019 Assets: Cash and cash equivalents $ 26,666 $ 26,666 $ — $ — Short-term investments 53,854 — 53,854 — Total assets $ 80,520 $ 26,666 $ 53,854 $ — December 31, 2018 Assets: Cash and cash equivalents $ 33,769 $ 29,270 $ 4,499 $ — Short-term investments 47,142 — 47,142 — Total assets $ 80,911 $ 29,270 $ 51,641 $ —
Summary of Available-for-Sale Securities	The following table summarizes the available-for-sale securities: Amortized Unrealized Unrealized Cost Gains Losses Fair Value (In thousands) June 30, 2019 Commercial paper $ 31,213 $ 44 $ — $ 31,257 Corporate bonds 22,085 13 — $ 22,098 Asset back securities 498 1 — $ 499 $ 53,796 $ 58 $ — $ 53,854 December 31, 2018 Commercial paper $ 22,619 $ — $ (15 ) $ 22,604 Corporate bonds 29,047 2 (12 ) 29,037 $ 51,666 $ 2 $ (27 ) $ 51,641

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	6 Months Ended
	Jun. 30, 2019
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following: June 30, 2019 December 31, 2018 (In thousands) Short-term deposits $ 3,147 $ 663 Prepaid clinical supplies 213 101 Interest receivable on investments 208 253 Reimbursable costs 677 797 Prepaid insurance 582 188 Other 327 332 Total prepaid expenses and other current assets $ 5,154 $ 2,334

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	6 Months Ended
	Jun. 30, 2019
Payables And Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: June 30, 2019 December 31, 2018 (In thousands) Accrued professional fees $ 425 $ 484 Accrued compensation and related costs 1,774 2,804 Accrued clinical costs 6,700 9,726 Accrued milestones 4,000 — Other 269 135 Total accrued expenses and other current liabilities $ 13,168 $ 13,149

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share Based Compensation Expense Related to Issuance of Stock Option Awards to Employees and Non Employees Related to Employee Stock Purchase Plan	The Company recognized stock-based compensation expense related to the issuance of stock option awards to employees and non-employees and related to the 2015 Employee Stock Purchase Plan (“ESPP”) in the condensed consolidated statements of comprehensive loss as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (In thousands) (In thousands) Research and development $ 537 $ 516 $ 1,071 $ 968 General and administrative 801 1,054 1,859 2,024 Total $ 1,338 $ 1,570 $ 2,930 $ 2,992
Compensation Expense by Type of Award	Compensation expense by type of award in the three and six months ended June 30, 2019 and 2018 was as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (In thousands) (In thousands) Stock options $ 1,308 $ 1,540 $ 2,867 $ 2,934 Employee Stock Purchase Plan 30 30 63 58 Total $ 1,338 $ 1,570 $ 2,930 $ 2,992

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Summary of Changes in Stockholders' Equity	The following table presents the changes in stockholders’ equity for the three and six months ended June 30, 2019: (In thousands, except share data) Common Stock $0.0001 Par Value Additional Paid-In Capital Accumulated Other Comprehensive Income / (Loss) Accumulated Deficit Total Stockholders’ Equity Shares Amount Balance as of January 1, 2019 24,835,951 $ 2 $ 492,493 $ (25 ) $ (439,423 ) $ 53,047 Stock purchase under ESPP 23,970 — — — — — Proceeds from 'at-the-market' offering, net of $34 offering expenses 140,819 — 830 — — 830 Stock-based compensation expense — — 1,592 — — 1,592 Proceeds from direct offering, net of $1,571 in common stock warrants, $78 offering expenses 2,095,039 1 10,921 — — 10,922 Proceeds from pre-funded common stock warrant from direct offering, net of $1,875 in common stock warrants, $93 offering expenses — — 13,032 — — 13,032 Issuance of common stock warrant with direct offering — — 3,446 — — 3,446 Unrealized gains on short-term investments — — — 33 — 33 Employee withholdings ESPP — — 26 — — 26 Net loss — — — — (14,302 ) (14,302 ) Balance as of March 31, 2019 27,095,779 $ 3 $ 522,340 $ 8 $ (453,725 ) $ 68,626 Stock-based compensation expense — — 1,338 — — 1,338 Offering expenses associated with direct offering — — (20 ) — — (20 ) Unrealized gains on short-term investments — — — 50 — 50 Employee withholdings ESPP — — 46 — — 46 Proceeds from exercise of stock options 22,167 — 151 — — 151 Net loss — — — — (14,916 ) (14,916 ) Balance as of June 30, 2019 27,117,946 $ 3 $ 523,855 $ 58 $ (468,641 ) $ 55,275 The following table represents the changes in stockholders’ equity for the three and six months ended June 30, 2018: (In thousands, except share data) Common Stock $0.0001 Par Value Additional Paid-In Capital Accumulated Other Comprehensive Income / (Loss) Accumulated Deficit Total Stockholders’ Equity Shares Amount Balance as of January 1, 2018 24,390,033 $ 2 $ 470,571 $ (143 ) $ (366,111 ) $ 104,319 Stock purchase under ESPP 8,696 — — — — — Stock-based compensation expense — — 1,421 — — 1,421 Stock issuance due to warrant exercise, cashless 299,215 — — — — — Unrealized gains on short-term investments — — — (75 ) — (75 ) Employee withholdings ESPP — — 34 — — 34 Cumulative effect adjustment of adoption ASU 2014-09 — — — — 649 649 Net loss — — — — (19,398 ) (19,398 ) Balance as of March 31, 2018 24,697,944 $ 2 $ 472,026 $ (218 ) $ (384,860 ) $ 86,951 Stock-based compensation expense — — 1,571 — — 1,571 Proceeds from exercise of stock options 7,850 — 26 — — 26 Unrealized gains on short-term investments — — — 129 — 129 Employee withholdings ESPP — — 63 — — 63 Retirement of common stock in exchange for common stock warrant 1 (2,000,000 ) — (16,780 ) — — (16,780 ) Issuance of common stock warrant in exchange for retirement of common stock 1 — — 16,780 — — 16,780 Net loss — — — — (18,388 ) (18,388 ) Balance as of June 30, 2018 22,705,794 $ 2 $ 473,686 $ (89 ) $ (403,247 ) $ 70,352 1 On June 18, 2018, the Company signed an exchange agreement with Biotechnology Value Fund and certain affiliated funds (“BVF”) under which BVF exchanged 2,000,000 shares of common stock for 2,000,000 warrant shares. The Company recorded the issuance of the warrant shares and the retirement of the common stock at fair value within additional paid-in capital. BVF can exercise the warrant shares at an exercise price per share equal to $0.0001 per share and the warrant shares expire 20 years from issuance. Per the terms of the warrant agreement, the outstanding warrants to purchase shares of common stock may not be exercised if the holder's ownership of the Company's common stock would exceed 9.99 percent following such exercise.

Nature of Business - Additional

Nature of Business - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segments	1
Date of incorporation	Oct. 11, 2005
State of incorporation	Delaware

Revenue from Contract with Cust

Revenue from Contract with Customer - Additional Information (Detail) - USD ($)	1 Months Ended		6 Months Ended	12 Months Ended
	Oct. 31, 2017	Dec. 19, 2014	Jun. 30, 2019	Dec. 31, 2017	Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Up-front payment allocated to preferred stock value
Kyowa Hakko Kirin Co., Ltd. [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Milestone payment agreement terms			In accordance with the terms of the license agreement
License Agreement [Member] | Kyowa Hakko Kirin Co., Ltd. [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
License agreement upfront payment received		$ 25,000,000
Up-front payment allocated to equity purchase		7,500,000
Up-front license fee received		$ 17,500,000
Period of termination after first commercial sale of first licensed product		15 years
Up-front payment allocated to preferred stock value		$ 7,700,000
Up-front payment allocated to license fee		17,300,000
Milestone payment received	$ 5,000,000			$ 5,000,000
Upfront payment allocation to performance obligation			$ 17,300,000
Performance obligation period			2029
Deferred revenue			$ 15,400,000
License Agreement [Member] | Kyowa Hakko Kirin Co., Ltd. [Member] | Maximum [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Milestone payment receivable upon achievement of development and commercial milestone		$ 75,000,000

Leases - Additional Information

Leases - Additional Information (Detail)	Sep. 30, 2016ft²	Dec. 31, 2015ft²	Jun. 30, 2019USD ($)	Jan. 01, 2019USD ($)	Dec. 31, 2018USD ($)
Lessee Lease Description [Line Items]
Right-of-use asset, net			$ 1,087,000	$ 1,300,000
Lease liability			$ 1,255,000	$ 1,300,000
Lease option to extend			true
Lease option to termination			true
Operating lease discount rate			14.00%
Operating lease expense			$ 243,000
Lease payments			282,000
Future minimum lease payments under capital leases			$ 11,000		$ 10,000
Waltham, Massachusetts [Member]
Lessee Lease Description [Line Items]
Operating lease term of contract	5 years
Area of leased property | ft²	12,207
Lease Commencement Date	Mar. 1, 2017
Remaining lease term			32 months
New York [Member]
Lessee Lease Description [Line Items]
Operating lease term of contract		62 months
Area of leased property | ft²		4,039
Lease Commencement Date		Jan. 1, 2016
Remaining lease term			20 months

Leases - Summary of Future Mini

Leases - Summary of Future Minimum Lease Payments under Operating Leases (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Operating Lease Liabilities Payments Due [Abstract]
2019	$ 285		$ 569
2020	585		588
2021	394		395
2022	59		59
Total lease payments	1,323		$ 1,611
Less: imputed interest	(68)
Total operating lease liability	$ 1,255	$ 1,300

Net Loss per Share Attributab_3

Net Loss per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator—basic and diluted:
Net loss	$ (14,916)	$ (14,302)	$ (18,388)	$ (19,398)	$ (29,218)	$ (37,785)
Net loss attributable to common stockholders—basic and diluted	$ (14,916)		$ (18,388)		$ (29,218)	$ (37,785)
Net loss per share attributable to common stockholders—basic and diluted	$ (0.47)		$ (0.74)		$ (1)	$ (1.54)
Denominator—basic and diluted:
Weighted-average number of common shares used to compute net loss per share attributable to common stockholders —basic and diluted	31,605,279		24,705,441		29,327,029	24,592,483

Net Loss per Share Attributab_4

Net Loss per Share Attributable to Common Stockholders - Potential Dilutive Securities Excluded from Computation of Diluted Net Loss per Common Share (Detail) - shares	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per common share	5,770,616	4,232,590
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per common share	4,595,039
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per common share	18,848	15,804

Net Loss per Share Attributab_5

Net Loss per Share Attributable to Common Stockholders - Additional Information (Detail) - $ / shares	Jun. 18, 2018	Mar. 31, 2019	Jun. 30, 2018
Earnings Per Share Basic [Line Items]
Warrant exercise price per share		$ 0.0001
Common stock, new shares issued		2,095,039
Warrant issued		2,500,000
Biotechnology Value Fund, L.P. [Member]
Earnings Per Share Basic [Line Items]
Number of common stock converted to warrants	2,000,000		2,000,000
Number of common stock warrants issued	2,000,000		2,000,000
Warrant exercise price per share	$ 0.0001		$ 0.0001

Significant Agreements - Additi

Significant Agreements - Additional Information (Detail) - USD ($)

Mar. 01, 2018

Jun. 30, 2019

Oct. 31, 2017

Jun. 30, 2014

Mar. 31, 2014

Dec. 31, 2007

Mar. 31, 2007

Jun. 30, 2019

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Mar. 31, 2017

Jun. 30, 2016

Jun. 30, 2019

Jun. 30, 2018

Dec. 31, 2016

Mar. 31, 2019

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Research and development expense

$ 12,290,000

$ 14,851,000

$ 23,569,000

$ 30,190,000

Warrant exercise price per share

$ 0.0001

Common Stock [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Issuance of common stock upon utilizing net exercise feature of warrant

299,215

Allergan License Agreement [Member] | Vitae Pharmaceuticals Inc [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Upfront milestone payable

$ 5,000,000

Potential milestone payments to be made

$ 99,000,000

Aggregate potential milestone payable

$ 70,000,000

License expiration year

10 years

Allergan License Agreement [Member] | Vitae Pharmaceuticals Inc [Member] | Accrued Milestone Expenses [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Research and development expense

$ 4,000,000

UCB License Agreement [Member] | UCB Biopharma [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Upfront milestone payable

$ 5,000,000

Potential milestone payments to be made

119,500,000

Aggregate potential milestone payable

$ 250,000,000

License expiration year

10 years

Research and development expense

$ 5,000,000

Clinical Trial [Member] | Eastern Cooperative Oncology Group [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Upfront milestone payable

$ 700,000

Milestone payment payable

$ 1,000,000

Increase in contractual obligation

$ 2,000,000

$ 800,000

Aggregate payment obligation

24,500,000

24,500,000

24,500,000

Remaining contractual obligation

$ 8,300,000

$ 8,300,000

$ 8,300,000

Period of contractual obligation

3 years

License Agreement [Member] | Bayer Pharma AG [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Research and development expense

$ 2,000,000

$ 2,000,000

Up-front license fee paid

$ 2,000,000

Percentage of shares issuable upon conversion of warrant

1.75%

Warrant exercise price per share

$ 1.54

Warrant expiration period

10 years

Proceeds from public stock offerings

$ 0

License Agreement [Member] | Bayer Pharma AG [Member] | Common Stock [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Issuance of common stock upon utilizing net exercise feature of warrant

299,215

License Agreement [Member] | Bayer Pharma AG [Member] | Maximum [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Aggregate payment obligation

$ 150,000,000

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Values of Financial Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 53,854	$ 47,142
Carrying Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	26,666	33,769
Short-term investments	53,854	47,142
Total assets	80,520	80,911
Quoted Prices (Unadjusted) in Active Markets Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	26,666	29,270
Total assets	26,666	29,270
Significant Other Observable Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents		4,499
Short-term investments	53,854	47,142
Total assets	$ 53,854	$ 51,641

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Fair Value Measurements [Line Items]
Available for sale debt securities fair value	$ 53,854,000		$ 51,641,000
Realized gains or losses recognized on the sale or maturity of available-for-sale securities	0	$ 0
Quoted Prices (Unadjusted) in Active Markets Level 1 [Member]
Fair Value Measurements [Line Items]
Cash equivalents fair value	26,666,000		29,270,000
Quoted Prices (Unadjusted) in Active Markets Level 1 [Member] | Overnight Investments, Money Market Funds and Highly Rated Corporate Bonds Member]
Fair Value Measurements [Line Items]
Cash equivalents fair value	26,700,000		29,300,000
Significant Other Observable Inputs Level 2 [Member]
Fair Value Measurements [Line Items]
Cash equivalents fair value			4,499,000
Significant Other Observable Inputs Level 2 [Member] | Corporate Bonds and Commercial Paper [Member]
Fair Value Measurements [Line Items]
Cash equivalents fair value			4,500,000
Significant Other Observable Inputs Level 2 [Member] | Commercial Paper, Corporate Bonds and Asset Backed Securities [Member] | Short-term Investments [Member]
Fair Value Measurements [Line Items]
Available for sale debt securities fair value	$ 53,900,000		$ 47,100,000

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 53,796	$ 51,666
Unrealized Gains	58	2
Unrealized Losses		(27)
Fair Value	53,854	51,641
Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	31,213	22,619
Unrealized Gains	44
Unrealized Losses		(15)
Fair Value	31,257	22,604
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	22,085	29,047
Unrealized Gains	13	2
Unrealized Losses		(12)
Fair Value	22,098	$ 29,037
Asset Back Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	498
Unrealized Gains	1
Fair Value	$ 499

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Short-term deposits	$ 3,147	$ 663
Prepaid clinical supplies	213	101
Interest receivable on investments	208	253
Reimbursable costs	677	797
Prepaid insurance	582	188
Other	327	332
Total prepaid expenses and other current assets	$ 5,154	$ 2,334

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued professional fees	$ 425	$ 484
Accrued compensation and related costs	1,774	2,804
Accrued clinical costs	6,700	9,726
Accrued milestones	4,000
Other	269	135
Total accrued expenses and other current liabilities	$ 13,168	$ 13,149

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exercised, shares	22,167	7,850	22,167	7,850
Proceeds from stock option exercises	$ 151,000	$ 26,000	$ 151,000	$ 26,000
Intrinsic value of options exercised			$ 7,000	$ 91,000
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance					993,438
2015 Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance	876,639		876,639
2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted to certain executives and employees			1,022,825
Options grant date fair value amount			$ 4,600,000
Weighted average grant date fair value of options			$ 4.47
Stock compensation expense			$ 80,000
Recognized compensation expense related to stock option not met			$ 0
2007 Plan [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted to certain executives and employees			583,000
2007 Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period to recognize compensation expense			4 years
2007 Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period to recognize compensation expense			1 year
2015 and 2007 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period to recognize compensation expense			2 years 4 months 24 days
Unrecognized compensation expense related to stock option	$ 11,200,000		$ 11,200,000

Stock-Based Compensation - Shar

Stock-Based Compensation - Share Based Compensation Expense Related to Issuance of Stock Option Awards to Employees and Non Employees Related to Employee Stock Purchase Plan (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	$ 1,338	$ 1,570	$ 2,930	$ 2,992
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	537	516	1,071	968
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	$ 801	$ 1,054	$ 1,859	$ 2,024

Stock-Based Compensation - Comp

Stock-Based Compensation - Compensation Expense by Type of Award (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	$ 1,338	$ 1,570	$ 2,930	$ 2,992
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	1,308	1,540	2,867	2,934
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	$ 30	$ 30	$ 63	$ 58

Employee Stock Purchase Plan -

Employee Stock Purchase Plan - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Employee Benefit Plans [Line Items]
Compensation expense		$ 1,338	$ 1,570	$ 2,930	$ 2,992
Employee Stock Purchase Plan [Member]
Employee Benefit Plans [Line Items]
Common stock available for issuance	248,359
Number of shares issued under plan				23,970
Compensation expense		$ 30	$ 30	$ 63	$ 58
Employee Stock Purchase Plan [Member] | Maximum [Member]
Employee Benefit Plans [Line Items]
Common stock available for issuance		875,842		875,842

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Changes in Stockholders' Equity (Detail) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Class of Stock [Line Items]
Beginning balance	$ 68,626	$ 53,047	$ 86,951	$ 104,319	$ 53,047	$ 104,319
Proceeds from 'at-the-market' offering, net, value		830
Stock-based compensation expense	1,338	1,592	1,571	1,421
Offering expenses associated with direct offering	(20)
Proceeds from direct offering, net, value		10,922
Proceeds from pre-funded common stock warrant from direct offering, net, value		13,032
Issuance of common stock warrant with direct offering, value		3,446
Unrealized gains on short-term investments	50	33	129	(75)	$ 83	$ 54
Employee withholdings ESPP	46	26	63	34
Retirement of common stock in exchange for common stock warrant			(16,780)
Issuance of common stock warrant in exchange for retirement of common stock			16,780
Proceeds from exercise of stock options, value	$ 151		$ 26
Proceeds from exercise of stock options, shares	22,167		7,850		22,167	7,850
Net loss	$ (14,916)	(14,302)	$ (18,388)	(19,398)	$ (29,218)	$ (37,785)
Ending balance	55,275	68,626	70,352	86,951	55,275	70,352
ASU 2014-09 [Member]
Class of Stock [Line Items]
Cumulative effect adjustment of adoption ASU 2014-09				649
Common Stock [Member]
Class of Stock [Line Items]
Beginning balance	$ 3	$ 2	$ 2	$ 2	$ 2	$ 2
Beginning balance, Shares	27,095,779	24,835,951	24,697,944	24,390,033	24,835,951	24,390,033
Stock purchase under ESPP, Shares		23,970		8,696
Proceeds from "at-the-market" offering, net, shares		140,819
Stock issuance due to warrant exercise, cashless, Shares				299,215
Proceeds from direct offering, net, value		$ 1
Proceeds from direct offering,net, Shares		2,095,039
Retirement of common stock in exchange for common stock warrant, shares			(2,000,000)
Proceeds from exercise of stock options, shares	22,167		7,850
Ending balance	$ 3	$ 3	$ 2	$ 2	$ 3	$ 2
Ending balance, Shares	27,117,946	27,095,779	22,705,794	24,697,944	27,117,946	22,705,794
Additional Paid-In Capital [Member]
Class of Stock [Line Items]
Beginning balance	$ 522,340	$ 492,493	$ 472,026	$ 470,571	$ 492,493	$ 470,571
Proceeds from 'at-the-market' offering, net, value		830
Stock-based compensation expense	1,338	1,592	1,571	1,421
Offering expenses associated with direct offering	(20)
Proceeds from direct offering, net, value		10,921
Proceeds from pre-funded common stock warrant from direct offering, net, value		13,032
Issuance of common stock warrant with direct offering, value		3,446
Employee withholdings ESPP	46	26	63	34
Retirement of common stock in exchange for common stock warrant			(16,780)
Issuance of common stock warrant in exchange for retirement of common stock			16,780
Proceeds from exercise of stock options, value	151		26
Ending balance	523,855	522,340	473,686	472,026	523,855	473,686
Accumulated Other Comprehensive Income / (Loss) [Member]
Class of Stock [Line Items]
Beginning balance	8	(25)	(218)	(143)	(25)	(143)
Unrealized gains on short-term investments	50	33	129	(75)
Ending balance	58	8	(89)	(218)	58	(89)
Accumulated Deficit [Member]
Class of Stock [Line Items]
Beginning balance	(453,725)	(439,423)	(384,860)	(366,111)	(439,423)	(366,111)
Net loss	(14,916)	(14,302)	(18,388)	(19,398)
Ending balance	$ (468,641)	$ (453,725)	$ (403,247)	(384,860)	$ (468,641)	$ (403,247)
Accumulated Deficit [Member] | ASU 2014-09 [Member]
Class of Stock [Line Items]
Cumulative effect adjustment of adoption ASU 2014-09				$ 649

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Changes in Stockholders' Equity (Parenthetical) (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jun. 18, 2018	Jun. 30, 2018	Jun. 30, 2019	Mar. 31, 2019
Class of Stock [Line Items]
At-the-market, offering expenses			$ 34
Direct offering, common stock warrants			1,571
Direct offering, offering expenses			78
Pre-funded common stock warrants			1,875
Pre-funded common stock warrants offering expenses			$ 93
Warrant exercise price per share				$ 0.0001
Biotechnology Value Fund, L.P. [Member]
Class of Stock [Line Items]
Number of common stock converted to warrants	2,000,000	2,000,000
Number of common stock warrants issued	2,000,000	2,000,000
Warrant exercise price per share	$ 0.0001	$ 0.0001
Warrant expiration period	20 years
Maximum percentage of common stock can be held upon exercise of warrant	9.99%

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended	4 Months Ended	6 Months Ended
	Mar. 31, 2019USD ($)Seriesofwarrant$ / sharesshares	Apr. 30, 2017USD ($)	Mar. 31, 2019USD ($)$ / sharesshares	Aug. 06, 2019shares	Jun. 30, 2019USD ($)$ / sharesshares
Class of Stock [Line Items]
Common stock, new shares issued | shares	2,095,039
Number of series of warrants | Seriesofwarrant	2
Warrant exercise price per share	$ 0.0001		$ 0.0001
Gross proceeds from offering | $	$ 27.6
Offering costs | $	$ 0.2
Weighted average expected term					1 year 4 months 24 days
Weighted Average Volatility Rate [Member]
Class of Stock [Line Items]
Warrants and rights outstanding, measurement input					0.891
Common Stock [Member]
Class of Stock [Line Items]
Common stock, new shares issued | shares	2,095,039
Pre-Funded Warrants [Member]
Class of Stock [Line Items]
Warrants issued (in shares) | shares	2,500,000		2,500,000
Warrant exercise price per share	$ 0.0001		$ 0.0001
Warrant term	20 years
Offering price	$ 5.9999
Series Warrants [Member]
Class of Stock [Line Items]
Warrants issued (in shares) | shares	4,595,039		4,595,039		4,595,039
Warrant term					90 days
Offering price	$ 6
Weighted average price					$ 12
Total fair value of warrant | $					$ 3.4
Series One Warrants
Class of Stock [Line Items]
Warrant exercise price per share					$ 12
Series Two Warrants
Class of Stock [Line Items]
Warrant exercise price per share					18
Minimum [Member] | Series Warrants [Member]
Class of Stock [Line Items]
Adjusted exercise price					$ 6
At The Market Equity Offering Sales Agreement [Member]
Class of Stock [Line Items]
Proceeds from issuance of common stock in follow-on public stock offering, net | $			$ 0.8
Common stock, new shares issued | shares			140,819
Subsequent Event [Member] | At The Market Equity Offering Sales Agreement [Member]
Class of Stock [Line Items]
Common stock, new shares issued | shares				0
Cowen and Company LLC [Member] | At The Market Equity Offering Sales Agreement [Member]
Class of Stock [Line Items]
Proceeds from issuance of common stock in follow-on public stock offering, net | $		$ 50
Cowen and Company LLC [Member] | At The Market Equity Offering Sales Agreement [Member] | Maximum [Member]
Class of Stock [Line Items]
Payment percentage of gross proceeds from sales agreement		3.00%