View Filing Data

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 24,609	$ 33,769
Restricted cash		101
Short-term investments	35,166	47,142
Prepaid expenses and other current assets	2,556	2,334
Total current assets	62,331	83,346
Property and equipment, net	281	373
Right-of-use asset	716
Other assets	197	219
Total assets	63,525	83,938
Current liabilities:
Accounts payable	6,178	1,439
Accrued expenses and other current liabilities	10,195	13,149
Current portion of deferred revenue	1,517	1,517
Current portion of right-of-use liability	478
Total current liabilities	18,368	16,105
Long-term liabilities:
Deferred revenue, less current portion	13,133	14,650
Right-of-use liability, less current portion	419
Other long-term liabilities	5	136
Total long-term liabilities	13,557	14,786
Total liabilities	31,925	30,891
Commitments (Note 14)
Stockholders' equity:
Preferred stock, $0.001 par value, 10,000,000 shares authorized; 0 shares outstanding at December 31, 2019 and December 31, 2018, respectively
Common stock, $0.0001 par value, 100,000,000 shares authorized; 27,140,484 and 24,835,951 shares outstanding at December 31, 2019 and December 31, 2018, respectively	3	2
Additional paid-in capital	527,067	492,493
Accumulated other comprehensive loss		(25)
Accumulated deficit	(495,470)	(439,423)
Total stockholders' equity	31,600	53,047
Total liabilities and stockholders' equity	$ 63,525	$ 83,938

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (56,047,000)	$ (73,961,000)	$ (60,802,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	92,000	78,000	76,000
Amortization and accretion of investments	(780,000)	(558,000)	223,000
Non-cash operating lease expense	359,000
Stock-based compensation	6,005,000	6,201,000	5,450,000
Other		11,000	8,000
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(52,000)	1,033,000	(329,000)
Accounts payable	4,739,000	(792,000)	(194,000)
Deferred revenue	(1,517,000)	(1,517,000)	2,892,000
Accrued expenses and other liabilities	(3,411,000)	974,000	5,305,000
Net cash used in operating activities	(50,612,000)	(68,531,000)	(47,371,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment		(187,000)	(84,000)
Purchases of short-term investments	(104,018,000)	(78,844,000)	(152,263,000)
Proceeds from sales and maturities of short-term investments	116,799,000	130,429,000	135,275,000
Net cash provided by (used in) investing activities	12,781,000	51,398,000	(17,072,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from Employee Stock Purchase Plan	182,000	198,000	97,000
Proceeds from exercise of stock options	178,000	26,000	277,000
Other		8,000
Net cash provided by financing activities	28,570,000	15,729,000	75,722,000
NET (DECREASE) INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(9,261,000)	(1,404,000)	11,279,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH—beginning of year	33,985,000	35,389,000	24,110,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH—end of year	24,724,000	33,985,000	35,389,000
Cash and cash equivalents	24,609,000	33,769,000	35,168,000
Restricted cash included in current and noncurrent assets	115,000	216,000	221,000
Follow-on Public Offering [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net			48,675,000
At-the-Market Offering [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net	830,000	$ 15,497,000	1,755,000
Private Placement [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net	$ 27,380,000		$ 24,918,000

Quarterly Financial Information (Unaudited) - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
License fees	$ 380	$ 379	$ 379	$ 379	$ 380	$ 379	$ 379	$ 379	$ 1,517	$ 1,517	$ 2,108
Type of revenue [extensible list]	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 9,502	$ 9,923	$ 12,290	$ 11,279	$ 15,821	$ 14,095	$ 14,851	$ 15,339	$ 42,994	$ 60,106	$ 48,201
General and administrative	5,083	3,605	3,463	3,911	3,892	4,125	4,479	4,791	16,062	17,287	15,861
Total operating expenses	14,585	13,528	15,753	15,190	19,713	18,220	19,330	20,130	59,056	77,393	64,062
Loss from operations	(14,205)	(13,149)	(15,374)	(14,811)	(19,333)	(17,841)	(18,951)	(19,751)	(57,539)	(75,876)	(61,954)
Other income	205	320	458	509	496	503	563	353	1,492	1,915	1,152
Net loss	$ (14,000)	$ (12,829)	$ (14,916)	$ (14,302)	$ (18,837)	$ (17,338)	$ (18,388)	$ (19,398)	$ (56,047)	$ (73,961)	$ (60,802)
Net loss per share attributable to common stockholders—basic and diluted	$ (0.44)	$ (0.41)	$ (0.47)	$ (0.53)	$ 0.70	$ 0.68	$ 0.74	$ 0.79	$ (1.84)	$ (2.92)	$ (2.90)
Weighted-average shares--basic and diluted	31,640,484	31,630,639	31,605,279	27,023,466	26,804,089	25,471,587	24,705,441	24,478,269	30,490,783	25,371,511	20,997,211

Significant Agreements

12 Months Ended

Dec. 31, 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 (“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 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. As a result, in 2017, the upfront payment of $5.0 million was recorded as research and development expense in the consolidated statements of operations. 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. The amount payable has been recorded in accounts payable as of December 31, 2019.

UCB Biopharma Sprl

In July 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 IND-ready anti-CSF-1R monoclonal antibody. The Company made a nonrefundable upfront payment of $5.0 million to UCB in the third quarter of 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 will be 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 in the consolidated statements of operations.

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 will provide 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. From the second quarter of 2016 through the fourth quarter of 2018, the Company has entered into a number of amendments to the agreement to provide for additional study activities resulting in an increase of the contractual obligation of $5.1 million. The total contractual costs under this agreement are $24.5 million. As of December 31, 2019, the Company’s maximum aggregate remaining payment obligations under the agreement are approximately $6.7 million, which are estimated to be paid over a period of approximately two 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 FDA or 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 up-front 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.

Common Stock - Additional Information (Detail) $ / shares in Units, $ in Millions				1 Months Ended				12 Months Ended	33 Months Ended
	Jan. 30, 2020 USD ($) $ / shares	Jul. 31, 2019 USD ($) shares	Jun. 18, 2018 $ / shares shares	Jan. 31, 2020 $ / shares shares	Aug. 31, 2019 USD ($) shares	Mar. 31, 2019 USD ($) Seriesofwarrant $ / shares shares	Apr. 30, 2017 USD ($)	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 $ / shares shares	Dec. 31, 2017 $ / shares
Class Of Stock [Line Items]
Common stock, shares authorized \| shares								100,000,000	100,000,000	100,000,000
Number of series of warrants \| Seriesofwarrant						2
Gross proceeds from offering \| $						$ 27.6
Offering costs \| $						$ 0.2
Common stock, par value								$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Weighted average expected term								1 year 4 months 24 days	1 year 4 months 24 days
Weighted Average Volatility Rate [Member]
Class Of Stock [Line Items]
Warrants and rights outstanding, measurement input								0.891	0.891
Subsequent Event [Member]
Class Of Stock [Line Items]
Common stock, new shares issued \| shares				3,036,719
Gross proceeds from offering \| $	$ 35.0
Common stock, par value				$ 0.0001
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
Warrant exercise price per share						$ 0.0001
Warrant term						20 years
Offering price						$ 5.9999
Maximum period allowed to increase beneficial ownership limitation after notice								61 days
Minimum percentage of common stock can be held upon exercise of warrant								9.99%
Maximum beneficial ownership limitation percentage								19.99%
Pre-Funded Warrants [Member] \| Biotechnology Value Fund, L.P. [Member]
Class Of Stock [Line Items]
Warrant exercise price per share			$ 0.0001
Number of common stock converted to warrants \| shares			2,000,000
Number of common stock warrants issued \| shares			2,000,000
Warrant expiration period			20 years
Maximum percentage of common stock can be held upon exercise of warrant			9.99%
Pre-Funded Warrants [Member] \| Subsequent Event [Member]
Class Of Stock [Line Items]
Warrants issued (in shares) \| shares				1,338,287
Offering price	$ 7.9999			$ 7.9999
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						$ 6.00
Weighted average price								$ 12.00
Total fair value of warrant \| $								$ 3.4
Series Warrants [Member] \| Subsequent Event [Member]
Class Of Stock [Line Items]
Offering price	8.00			8.00
Series One Warrants [Member]
Class Of Stock [Line Items]
Warrant exercise price per share								$ 12.00	$ 12.00
Series One Warrants [Member] \| Subsequent Event [Member]
Class Of Stock [Line Items]
Warrant exercise price per share	10.00
Series Two Warrants [Member]
Class Of Stock [Line Items]
Warrant exercise price per share								18.00	$ 18.00
Series Two Warrants [Member] \| Subsequent Event [Member]
Class Of Stock [Line Items]
Warrant exercise price per share	$ 13.00
Maximum [Member] \| Series One Warrants [Member] \| Subsequent Event [Member]
Class Of Stock [Line Items]
Warrant exercise price per share				12.00
Maximum [Member] \| Series Two Warrants [Member] \| Subsequent Event [Member]
Class Of Stock [Line Items]
Warrant exercise price per share				18.00
Minimum [Member] \| Series Warrants [Member]
Class Of Stock [Line Items]
Adjusted exercise price								6.00
Minimum [Member] \| Series One Warrants [Member] \| Subsequent Event [Member]
Class Of Stock [Line Items]
Warrant exercise price per share				10.00
Minimum [Member] \| Series Two Warrants [Member] \| Subsequent Event [Member]
Class Of Stock [Line Items]
Warrant exercise price per share				$ 13.00
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							$ 18.2
Common stock, new shares issued \| shares		140,819			0				2,403,409
Sale of stock, price per share								$ 7.82	$ 7.82
Gross proceeds from issuance of common stock \| $									$ 18.8
Proceeds from issuance of common stock, net \| $		$ 0.8							$ 18.2
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 \| $					$ 50.0		$ 50.0
Proceeds from issuance of common stock, net \| $					$ 50.0		$ 50.0
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%
Initial Public Offering [Member]
Class Of Stock [Line Items]
Common stock, shares authorized \| shares								100,000,000	100,000,000

Income Taxes - Components of Deferred Tax (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets (liabilities):
Net operating loss carryforwards	$ 16,410	$ 12,684
Research and development credits	4,156	3,443
Capitalized start-up and research and development costs, net	55,452	59,331
Deferred revenue	3,334	3,690
Depreciation and amortization of capitalized cost	13	(11,550)
Accruals	828	630
Other temporary differences	4,223	3,423
Deferred tax assets before valuation allowance	84,416	71,651
Valuation allowances	$ (84,416)	$ (71,651)

Significant Agreements - Additional Information (Detail) - USD ($)		1 Months Ended							3 Months Ended										12 Months Ended
	Mar. 01, 2018	Jun. 30, 2019	Oct. 31, 2017	Jul. 31, 2016	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2007	Mar. 31, 2007	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense									$ 9,502,000	$ 9,923,000	$ 12,290,000	$ 11,279,000	$ 15,821,000	$ 14,095,000	$ 14,851,000	$ 15,339,000			$ 42,994,000	$ 60,106,000	$ 48,201,000
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	$ 5,000,000
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													$ 5,100,000
Aggregate payment obligation									24,500,000										$ 24,500,000
Period of contractual obligation																			2 years
Clinical Trial [Member] \| Eastern Cooperative Oncology Group [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Remaining contractual obligation									$ 6,700,000										$ 6,700,000
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

Leases

12 Months Ended

Dec. 31, 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 a lease asset and lease liability of approximately $1.3 million as of January 1, 2019. ASC 842 did not materially impact the Company’s 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 December 31, 2019 for the facility in Waltham, Massachusetts and New York, New York, were 26 months and 14 months, respectively. As of December 31, 2019, the consolidated balance sheet includes a $0.7 million operating lease ROU asset and a $0.9 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 year ended December 31, 2019, the Company recorded approximately $447,000 in operating lease expense and made approximately $566,000 in lease payments.

Future minimum lease payments under the Company’s operating leases as of December 31, 2019 and 2018, were as follows:

Maturity of lease liabilities	As of			As of
(in thousands)	December 31, 2019			December 31, 2018
2019	$	—		$	569
2020		585			588
2021		394			395
2022		59			59
Thereafter		—			—
Total lease payments	$	1,038		$	1,611
Less: imputed interest		(141	)
Total operating lease liability	$	897

Future minimum lease payments under the Company’s capital leases as of December 31, 2019 and 2018, were $9,000 and $14,000, respectively.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

13. Stock-Based Compensation

In September 2015, the Company’s board of directors adopted its 2015 Omnibus Incentive Plan (“2015 Plan”), which was subsequently approved by its stockholders and became effective upon the closing of the IPO on March 8, 2016. The 2015 Plan replaced the 2007 Stock Plan (“2007 Plan”) and allows for the granting of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock, unrestricted stock, stock units, dividend equivalent rights, performance awards, annual incentive awards, and other equity-based awards to the Company’s executives and other employees, non-employee members of the board of directors, and consultants of the Company. Any options or awards outstanding under the Company’s 2007 Plan remain outstanding and effective. Any shares of common stock related to awards outstanding under the 2007 Plan that thereafter terminate by expiration, forfeiture, cancellation or otherwise without the issuance of such shares will be added to, and included in, the 2015 Plan reserve amount. The Company initially reserved 1,750,000 shares of its common stock for the issuance of awards under the 2015 Plan. As of December 31, 2019, there were 586,554 shares available for issuance under the 2015 Plan.

The 2015 Plan provides that the number of shares reserved and available for issuance under the 2015 Plan will automatically increase each January 1, beginning on January 1, 2017, by 4% of the outstanding number of shares of common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Company’s board of directors. On January 1, 2020, the shares available for issuance under the 2015 Plan were increased to 1,672,173.

The Company recognized stock-based compensation expense related to the issuance of stock option awards to employees and non-employees and related to the Employee Stock Purchase Plan in the consolidated statements of operations as follows (in thousands):

	Years Ended December 31,
	2019		2018		2017
Research and development	$	2,061	$	1,910	$	1,363
General and administrative		3,944		4,291		4,087
Total	$	6,005	$	6,201	$	5,450

Stock Options

As of December 31, 2019, there was $10.1 million of unrecognized compensation cost related to employee and non-employee unvested stock options granted under the 2007 and 2015 Plans, which is expected to be recognized over a weighted-average remaining service period of 2.3 years. Stock compensation costs have not been capitalized by the Company. As of December 31, 2019, there was $0.7 million of unrecognized compensation cost related to performance-based options, and $9.4 million of unrecognized compensation expense related to service based options.

Our stock-based awards are subject to either service or performance-based vesting conditions. Compensation expense related to awards to employees, directors and non-employees with service-based vesting conditions is recognized on a straight-line basis based on the grant date fair value over the associated service period of the award, which is generally the vesting term. Compensation expense related to awards to employees with performance-based vesting conditions is recognized based on the grant date fair value over the requisite service period using the straight-line method to the extent achievement of the performance condition is probable.

In 2017, the Company granted 60,000 options with performance conditions, 13,333 of which have vested in 2019, and 6,667 of which have been cancelled as of December 31, 2019. In the years ended December 31, 2019, 2018 and 2017, the Company recorded approximately $88,000, $142,000 and $29,000, respectively, of stock compensation expense associated with these awards.

In 2019, the Company granted to certain employees 583,000 stock options that contain 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 $181,000 of stock compensation expense associated with these awards for the year ended December 31, 2019. For the remaining milestones, achievement of the performance conditions was considered not probably, nor met, and therefore no expense has been recognized related to these awards for the year ended December 31, 2019.

The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model with the weighted-average assumptions noted in the table below. Expected volatility for the Company’s common stock was determined based on an average of the historical volatility of a peer group of similar public companies. The Company estimated the expected term of its employee stock options using the “simplified” method, whereby, the expected term equals the average of the vesting term and the original contractual term of the option. The contractual life of the option was used for the estimated life of the non-employee grants. The assumed dividend yield is based upon the Company’s expectation of not paying dividends in the foreseeable future. The risk-free interest rate for periods within the expected life of the option is based upon the U.S. Treasury yield curve in effect at the time of grant. The Company accounts for forfeitures when they occur. The grant date fair values of options issued to employees and non-employees were estimated using the Black-Scholes option-pricing model with the following assumptions:

	Years Ended December 31,
	2019			2018			2017
Expected term (in years)		5.97			5.90			6.02
Volatility rate		76.95	%		76.28	%		73.86	%
Risk-free interest rate		2.29	%		2.69	%		2.02	%
Expected dividend yield		0.00	%		0.00	%		0.00	%

A summary of employee and non-employee option activity under the Company’s equity award plans is presented below (in thousands, except share data):

	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding—January 1, 2019		4,252,983		$	9.23		7.3	$	66
Granted		1,964,025		$	6.99
Exercised		(25,857	)	$	6.86
Canceled or forfeited		(134,140	)	$	9.85
Outstanding—December 31, 2019		6,057,011		$	8.50		7.2	$	6,306
Exercisable—December 31, 2019		3,620,626		$	8.93		6.1	$	3,114
Options vested, exercisable or expected to vest—December 31, 2019		5,655,008		$	8.64		7.1	$	5,373

The weighted-average grant date fair value of options granted during the years ended December 31, 2019, 2018 and 2017, was $4.81, $6.17, and $6.68 per share, respectively. The fair value is being expensed over the vesting period of the options (usually three to four years) on a straight-line basis as the services are being provided.

There were 25,857 options exercised for the year ended December 31, 2019, resulting in total proceeds of $178,000; 7,850 options exercised for the year ended December 31, 2018, resulting in total proceeds of $26,000; and 46,680 options exercised for the year ended December 31, 2017, resulting in total proceeds of $0.3 million. The intrinsic value of options exercised during the years ended December 31, 2019, 2018 and 2017 was $9,000, $0.1 million, and $0.2 million, respectively. In accordance with the Company’s policy, the shares were issued from a pool of shares reserved for issuance under the 2007 and 2015 Plans.

Employee Stock Purchase Plan

In September 2015, the Company’s Board adopted the Employee Stock Purchase Plan (the “ESPP”), which was subsequently approved by the Company’s stockholders in February 2016 and became effective upon the closing of the IPO on March 8, 2016. The ESPP authorizes the initial issuance of up to a total of 250,000 shares of common stock to the Company’s employees. The Company issued 42,818 shares during 2019. On January 1, 2020, the shares of common stock reserved for issuance under the ESPP was increased to 1,128,398. Under the terms of the ESPP, eligible employees can elect to acquire shares of the Company’s common stock through periodic payroll deductions during a series of six month offering periods. Purchases under the ESPP are effected on the last business day of each offering period at a 15% discount to the lower of closing price on that day or the closing price on the first day of the offering period.

The ESPP is considered a compensatory plan with the related compensation cost expensed over the six-month offering period. For the years ended December 31, 2019, 2018 and 2017 the Company recorded stock-based compensation expense related to the ESPP of $113,000, $132,000 and $42,000 respectively.

Employee Benefit Plan

The Company has a Section 401(k) defined contribution savings plan for its employees. The plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pretax basis, subject to legal limitations. Company contributions to the plan may be made at the discretion of the Board. For the years ended December 31, 2019, 2018 and 2017, the Company made $119,000, $126,000 and $106,000 contributions to the plan, respectively.

Net Loss per Share Attributable to Common Stockholders

12 Months Ended

Dec. 31, 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 attributable to common stockholders per share 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 the three years ended December 31, 2019, 2018, and 2017, 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 (in thousands, except per share data):

	Years Ended December 31,
	2019			2018			2017
Numerator--basic and diluted:
Net loss	$	(56,047	)	$	(73,961	)	$	(60,802	)
Net loss attributable to common stockholders--basic and diluted	$	(56,047	)	$	(73,961	)	$	(60,802	)
Net loss per share—basic and diluted	$	(1.84	)	$	(2.92	)	$	(2.90	)
Denominator—basic and diluted:
Weighted-average common shares used to compute net loss per share—basic and diluted		30,490,783			25,371,511			20,997,211

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):

	December 31,
	2019		2018		2017
Options to purchase common stock		6,057,011		4,252,983		3,391,832
Common stock warrants		4,595,039		—		357,840
ESPP shares		15,223		29,736		—

As discussed in Note 12, 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 pre-funded warrant shares. Further, in March 2019, the Company sold an additional 2,500,000 pre-funded warrant shares. The pre-funded warrants are exercisable into shares of common stock for $0.0001 per share. The shares of common stock into which the pre-funded warrants may be exercised are considered outstanding for the purposes of computing earnings per share.

Quarterly Financial Information (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information

The following table contains quarterly financial information for 2019 and 2018. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period.

	Three Months Ended
	2019
In thousands, except per share data	March 31			June 30			September 30			December 31
License fees	$	379		$	379		$	379		$	380
Operating expenses:
Research and development		11,279			12,290			9,923			9,502
General and administrative		3,911			3,463			3,605			5,083
Total expenses		15,190			15,753			13,528			14,585
Loss from operations		(14,811	)		(15,374	)		(13,149	)		(14,205	)
Other income		509			458			320			205
Net loss	$	(14,302	)	$	(14,916	)	$	(12,829	)	$	(14,000	)
Net loss per share attributable to common stockholders—basic and diluted	$	(0.53	)	$	(0.47	)	$	(0.41	)	$	(0.44	)
Weighted-average shares--basic and diluted		27,023,466			31,605,279			31,630,639			31,640,484

	Three Months Ended
	2018
In thousands, except per share data	March 31			June 30			September 30			December 31
License fees	$	379		$	379		$	379		$	380
Operating expenses:
Research and development		15,339			14,851			14,095			15,821
General and administrative		4,791			4,479			4,125			3,892
Total expenses		20,130			19,330			18,220			19,713
Loss from operations		(19,751	)		(18,951	)		(17,841	)		(19,333	)
Other income		353			563			503			496
Net loss	$	(19,398	)	$	(18,388	)	$	(17,338	)	$	(18,837	)
Net loss per share attributable to common stockholders—basic and diluted	$	0.79		$	0.74		$	0.68		$	0.70
Weighted-average shares--basic and diluted		24,478,269			24,705,441			25,471,587			26,804,089

Revenue from Contract with Customers - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Oct. 31, 2017	Dec. 19, 2014	Dec. 31, 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 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 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			$ 14,700,000
License Agreement [Member] \| Kyowa 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

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Mar. 04, 2020	Jun. 30, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
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
Title of 12(b) Security	Common Stock
Entity Common Stock, Shares Outstanding		30,240,838
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-37708
Entity Tax Identification Number	32-0162505
Entity Address, Address Line One	35 Gatehouse Drive
Entity Address, Address Line Two	Building D
Entity Address, Address Line Three	Floor 3
Entity Address, City or Town	Waltham
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02451
City Area Code	781
Local Phone Number	419-1400
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Security Exchange Name	NASDAQ
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Public Float			$ 208.3
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement for its 2020 Annual Meeting of Stockholders, which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year ended December 31, 2019, are incorporated by reference into Part III of this Annual Report on Form 10-K.

Common Stock

12 Months Ended

Dec. 31, 2019

Text Block [Abstract]

Common Stock

12. Common Stock

In connection with the closing of the Company’s IPO, the Company filed an amended and restated certificate of incorporation and adopted amended and restated bylaws; and pursuant to the amended and restated certificate of incorporation, the Company is authorized to issue 100,000,000 shares of common stock. The holders of each share of common stock are entitled to one vote per share held and are entitled to receive dividends, if and when declared by the Board, and to share ratably in the Company’s assets available for distribution to stockholders, in the event of liquidation.

In April 2017, the Company entered into a sales agreement with 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 ATM equity offerings (the “2017 ATM Program”). Since inception of the ATM program in 2017, the Company has sold 2,403,409 shares of common stock pursuant to the ATM program, at an average price of $7.82 per share for gross proceeds of $18.8 million, resulting in net proceeds of $18.2 million after deducting sales commissions and offering expenses. The 2017 ATM Program was replaced by the 2019 ATM Program.

In August 2019, the Company entered into a new sales agreement with Cowen and Company, LLC (“Cowen”) under which the Company may issue and sell shares of its 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 (the “2019 ATM Program”). Cowen is not required to sell any specific amount, but acts as the Company’s sales agent using commercially reasonable efforts consistent with its normal trading and sales practices. Shares sold pursuant to the sales agreement will be sold pursuant to a shelf registration statement on Form S-3 (Registration No. 333-233564), which was declared effective on September 10, 2019. The Company’s common stock will be sold at prevailing market prices at the time of the sale; and as a result, prices may vary. The Company pays Cowen up to 3% of the gross proceeds from any common stock sold through this sales agreement. In 2019, prior to the effectiveness of the 2019 ATM Program, the Company sold 140,819 shares of common stock under the 2017 ATM program for net proceeds of $0.8 million. No shares of common stock have been sold under the 2019 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 (as described below). 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 (other than Exempted Securities as defined by the Series Warrant) 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.

In January 2020, the Company sold 3,036,719 shares of common stock, par value $0.0001 per share (“Common Stock”) and Pre-Funded Warrants to purchase 1,338,287 shares of Common Stock (the “Pre-Funded Warrants”). The offering price for the securities was $8.00 per share or $7.9999 for each Pre-Funded Warrant. As a result of this offering, the exercise price of Series 1 and Series 2 Warrants outstanding reset from $12.00 per share to $10.00 per share and from $18.00 per share to $13.00, respectively.

The Pre-Funded Warrants and the Series Warrants may not be exercised by the holder to the extent that the holder, together with its affiliates, would beneficially own, after such exercise more than 9.99% of the shares of the Company’s common stock then outstanding (subject to the right of the holder to increase or decrease such beneficial ownership limitation upon notice to the Company, provided that such limitation cannot exceed 19.99%) and provided that any increase in the beneficial ownership limitation shall not be effective until 61 days after such notice is delivered.

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. The Company valued the Series Warrants at issuance using the Black Scholes option pricing model and determined the fair value of the 4,595,039 Series Warrants at $3.4 million. The key inputs to the valuation model included the weighted average volatility of 89.1% and the weighted average expected term of 1.4 years.

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 Pre-Funded Warrant shares. The Company recorded the issuance of the Pre-Funded Warrants and the retirement of the common stock at fair value within additional paid-in capital. BVF can exercise the Pre-Funded Warrants at an exercise price per share equal to $0.0001 per share and the Pre-Funded Warrants expire 20 years from issuance. Per the terms of the warrant agreement, the outstanding Pre-Funded Warrants may not be exercised if the holder's ownership of the Company's common stock would exceed 9.99 percent following such exercise.

The Company has reserved for future issuance the following shares of common stock related to the potential warrant exercise, exercise of stock options, and the employee stock purchase plan:

	December 31, 2019
Common stock issuable under pre-funded warrants		4,500,000
Series 1 and 2 warrants		4,595,039
Options to purchase common stock		6,643,565
Employee Stock Purchase Plan		856,994
Total		16,595,598

Fair Value Measurements

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements

9. 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 years 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 during the years ended December 31, 2019, 2018 and 2017.

A summary of the assets and liabilities carried at fair value in accordance with the hierarchy defined above is as follows (in thousands):

			Fair Value Measurements Using
	Total Carrying Value		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
December 31, 2019
Assets:
Cash equivalents	$	24,609	$	23,439	$	1,170	$	—
Short-term investments		35,166		—		35,166		—
Total assets	$	59,775	$	23,439	$	36,336	$	—
December 31, 2018
Assets:
Cash equivalents	$	33,769	$	29,270	$	4,499	$	—
Short-term investments		47,142		—		47,142		—
Total assets	$	80,911	$	29,270	$	51,641	$	—

Cash equivalents of $23.4 million as of December 31, 2019 and $29.3 million as of December 31, 2018 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 $1.2 million as of December 31, 2019 and $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 $35.2 million as of December 31, 2019 and $47.1 million as of December 31, 2018, consisted of commercial paper and highly rated corporate bonds 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 December 31, 2019, the remaining contractual maturities of the available-for-sale securities were less than 12 months, 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 years ended December 31, 2019. 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 December 31, 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 (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2019
Commercial paper	$	15,675	$	5	$	—		$	15,680
Corporate bonds		18,361		—		(5	)		18,356
Asset back securities		2,300		—		—			2,300
	$	36,336	$	5	$	(5	)	$	36,336
December 31, 2018
Commercial paper	$	22,619	$	—	$	(15	)	$	22,604
Corporate bonds		29,047		2		(12	)		29,037
	$	51,666	$	2	$	(27	)	$	51,641

Quarterly Financial Information (Unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information (Unaudited)

18. Quarterly financial information (unaudited)

	Three Months Ended
	2019
In thousands, except per share data	March 31			June 30			September 30			December 31
License fees	$	379		$	379		$	379		$	380
Operating expenses:
Research and development		11,279			12,290			9,923			9,502
General and administrative		3,911			3,463			3,605			5,083
Total expenses		15,190			15,753			13,528			14,585
Loss from operations		(14,811	)		(15,374	)		(13,149	)		(14,205	)
Other income		509			458			320			205
Net loss	$	(14,302	)	$	(14,916	)	$	(12,829	)	$	(14,000	)
Net loss per share attributable to common stockholders—basic and diluted	$	(0.53	)	$	(0.47	)	$	(0.41	)	$	(0.44	)
Weighted-average shares--basic and diluted		27,023,466			31,605,279			31,630,639			31,640,484

	Three Months Ended
	2018
In thousands, except per share data	March 31			June 30			September 30			December 31
License fees	$	379		$	379		$	379		$	380
Operating expenses:
Research and development		15,339			14,851			14,095			15,821
General and administrative		4,791			4,479			4,125			3,892
Total expenses		20,130			19,330			18,220			19,713
Loss from operations		(19,751	)		(18,951	)		(17,841	)		(19,333	)
Other income		353			563			503			496
Net loss	$	(19,398	)	$	(18,388	)	$	(17,338	)	$	(18,837	)
Net loss per share attributable to common stockholders—basic and diluted	$	0.79		$	0.74		$	0.68		$	0.70
Weighted-average shares--basic and diluted		24,478,269			24,705,441			25,471,587			26,804,089

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

14. Income Taxes

The Company has not recorded any net tax provision for the periods presented due to the losses incurred and the need for a full valuation allowance on deferred tax assets. The difference between the income tax expense at the U.S. federal statutory rate and the recorded provision is primarily due to the valuation allowance provided on all deferred tax assets. The Company’s loss before income tax for the periods presented was generated entirely in the United States.

The significant components of the Company’s deferred tax are as follows (in thousands):

	Years Ended December 31,
	2019			2018
Deferred tax assets (liabilities):
Net operating loss carryforwards	$	16,410		$	12,684
Research and development credits		4,156			3,443
Capitalized start-up and research and development costs, net		55,452			59,331
Deferred revenue		3,334			3,690
Depreciation and amortization of capitalized cost		13			(11,550	)
Accruals		828			630
Other temporary differences		4,223			3,423
Deferred tax assets before valuation allowance		84,416			71,651
Valuation allowances		(84,416	)		(71,651	)
Net deferred tax assets	$	—		$	—

The Company has provided a valuation allowance for the full amount of the net deferred tax assets as the realization of the deferred tax assets is not determined to be more likely than not. The valuation allowance increased by $12.8 million and $17.2 million in 2019 and 2018, respectively, due to the increase in deferred tax assets, primarily due to net operating loss carryforwards and capitalized research and development costs.

As of December 31, 2019, the Company had approximately $68.0 million and $33.1 million in federal and state Net Operating Losses (“NOLs”), respectively, which begin to expire at various dates starting in 2025. As of December 31, 2019, the Company had federal and state research credits of $2.9 million and $1.6 million, respectively, which begin to expire in 2021.

Realization of future tax benefits is dependent on many factors, including the Company’s ability to generate taxable income within the net operating loss carryforward period. Under the Internal Revenue Code provisions, certain substantial changes in the Company’s ownership, including the sale of the Company or significant changes in ownership due to sales of equity, may have limited, or may limit in the future, the amount of net operating loss carryforwards which could be used annually to offset future taxable income. The Company completed an analysis through March 31, 2019 and determined that on March 30, 2007 and August 21, 2015 ownership changes had occurred. The Company may also experience ownership changes in the future as a result of subsequent shifts in our stock ownership, some of which may be outside of our control. As a result, its ability to use its pre-change NOLs to offset U.S. federal taxable income may be subject to limitations, which could potentially result in increased future tax liability. In addition, at the state level, there may be periods during which the use of NOLs is suspended or otherwise limited, which could accelerate or permanently increase state taxes owed.

As of December 31, 2019, and 2018, the Company had uncertain tax positions of $0.2 million related to capitalized research and development costs and research and development credits, which reduce the deferred tax assets with a corresponding decrease to the valuation allowance. The Company has elected to recognize interest and penalties related to income tax matters as a component of income tax expense, of which no interest or penalties were recorded for the years ended December 31, 2019 and 2018. The Company expects none of the unrecognized tax benefits to decrease within the next 12 months related to expired statutes or settlement with the taxing authorities. Due to the Company’s valuation allowance as of December 31, 2019, none of the Company’s unrecognized tax benefits, if recognized, would affect the effective tax rate.

A reconciliation of the Company’s unrecognized tax benefits is as follows (in thousands):

	Years Ended December 31,
	2019		2018		2017
Unrecognized tax benefit--beginning of year	$	163	$	163	$	241
Decreases related to prior period positions		—		—		(78	)
Unrecognized tax benefit--end of year	$	163	$	163	$	163

The Company files tax returns in the United States, Massachusetts, California, New Jersey, New York, and Pennsylvania. All tax years since inception (October 11, 2005) remain open to examination by major tax jurisdictions to which the Company is subject, as carryforward attributes generated in years past may still be adjusted upon examination by the Internal Revenue Service or state tax authorities if they have or will be used in a future period. The Company is currently not under examination by the Internal Revenue Service or any other jurisdictions for any tax years.

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total revenues	$ 1,517	$ 1,517	$ 2,108
Type of revenue [extensible list]	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 42,994	$ 60,106	$ 48,201
General and administrative	16,062	17,287	15,861
Total operating expenses	59,056	77,393	64,062
Loss from operations	(57,539)	(75,876)	(61,954)
Other income (expense):
Interest income (expense), net	1,571	1,942	1,421
Other (expense) income, net	(79)	(27)	(269)
Total other income (expense)	1,492	1,915	1,152
Net loss	(56,047)	(73,961)	(60,802)
Net loss attributable to common stockholders	$ (56,047)	$ (73,961)	$ (60,802)
Net loss per share attributable to common stockholders—basic and diluted	$ (1.84)	$ (2.92)	$ (2.90)
Weighted-average common shares outstanding—basic and diluted	30,490,783	25,371,511	20,997,211

Stock-Based Compensation - Summary of Company's Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Arrangements To Obtain Goods And Services [Abstract]
Options outstanding, Beginning balance	4,252,983
Options granted	1,964,025
Options exercised	(25,857)	(7,850)	(46,680)
Options cancelled or forfeited	(134,140)
Options outstanding, Ending balance	6,057,011	4,252,983
Options exercisable, Ending balance	3,620,626
Options vested, exercisable or expected to vest, Ending balance	5,655,008
Options outstanding, Weighted Average Exercise Price, Beginning balance	$ 9.23
Options granted, Weighted Average Exercise Price	6.99
Options exercised, Weighted Average Exercise Price	6.86
Options canceled or forfeited, Weighted Average Exercise Price	9.85
Options outstanding, Weighted Average Exercise Price, Ending balance	8.50	$ 9.23
Options exercisable, Weighted Average Exercise Price, Ending balance	8.93
Options vested, exercisable or expected to vest, Weighted Average Exercise Price, Ending balance	$ 8.64
Options outstanding, Weighted Average Remaining Contractual Term	7 years 2 months 12 days	7 years 3 months 18 days
Options exercisable, Weighted Average Remaining Contractual Term, Ending balance	6 years 1 month 6 days
Options vested, exercisable or expected to vest, Weighted Average Remaining Contractual Term, Ending balance	7 years 1 month 6 days
Options outstanding, Aggregate Intrinsic Value	$ 6,306	$ 66
Options exercisable, Aggregate Intrinsic Value	3,114
Options vested, exercisable or expected to vest, Aggregate Intrinsic Value	$ 5,373

Basis of Presentation (Policies)	12 Months Ended
Basis of Presentation (Policies)	Dec. 31, 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 consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of 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 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.
Cash Equivalents	Cash Equivalents Cash equivalents include all highly liquid investments maturing within 90 days or less from the date of purchase. Cash equivalents include money market funds, corporate debt securities, U.S. government agency notes, and overnight deposits.
Restricted Cash	Restricted Cash The Company classifies as restricted cash all cash pledged as collateral to secure long-term obligations and all cash whose use is otherwise limited by contractual provisions. Amounts are reported as non-current unless restrictions are expected to be released in the next 12 months.
Short-Term Investments	Short-Term Investments Short-term investments include marketable securities with maturities of less than one year or where management’s intent is to use the investments to fund current operations or to make them available for current operations. Long-term investments include marketable securities with remaining maturities greater than one year or that are due after one year from the balance sheet date. All investments in marketable securities are classified as available-for-sale and are reported at fair value with unrealized gains and losses excluded from earnings and reported net of tax in accumulated other comprehensive income, which is a component of stockholders’ equity (deficit). Unrealized losses that are determined to be other-than-temporary, based on current and expected market conditions, are recognized in earnings. Declines in fair value determined to be credit related are charged to earnings. The cost of marketable securities sold is determined by the specific identification method.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision-making group, in making decisions regarding resource allocation and assessing performance. The Company has one operating segment.
Concentrations of Credit Risk	Concentrations of Credit Risk Cash and cash equivalents, restricted cash, and short-term and long-term investments are financial instruments that potentially subject the Company to concentrations of credit risk. Substantially all of the Company’s cash, cash equivalents, and short-term investments were deposited in accounts at two financial institutions, and at times, such deposits may exceed federally insured limits. The Company has not experienced any losses in such accounts, and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. The Company’s available-for-sale investments primarily consist of government money market funds, corporate debt securities, commercial paper, credit card asset-backed securities and overnight deposits and potentially subject the Company to concentrations of credit risk.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost. Depreciation is recorded using the straight-line method over the estimated useful lives of the assets (three to five years). Assets under capital leases are amortized over the shorter of their useful lives or lease term using the straight-line method. Major replacements and improvements are capitalized, while general repairs and maintenance are expensed as incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. When such events occur, the Company compares the carrying amounts of the assets to their undiscounted expected future cash flows. If this comparison indicates that there is impairment, the amount of impairment is calculated as the difference between the carrying value and fair value. To date, no such impairments have been recognized.
Revenue Recognition	Revenue Recognition The Company adopted Accounting Standards Codification (“ASC”) Rule 606 Revenue from Contracts with Customers (ASC 606), on January 1, 2018, using the modified retrospective method for all contracts not completed as of the date of adoption. The reported results for 2018 reflect the application of ASC 606 guidance while the reported results for 2017 were prepared under the guidance of ASC 605, Revenue Recognition (ASC 605). As of January 1, 2018, the Company had only one contract within the scope of ASC 606, a license agreement with Kyowa Kirin Co., Ltd. (“KKC”), under which the Company granted KKC an exclusive license to develop and commercialize entinostat in Japan and Korea (the “KKC License Agreement”). The KKC License Agreement is discussed further in Note 4. The Company enters into license agreements for the development and commercialization of its product candidates. License agreements may include non-refundable upfront payments, contingent payments based on the occurrence of specified events under the Company’s license arrangements, partial or complete reimbursement of research and development expenses, license fees and royalties on sales of entinostat if they are successfully approved and commercialized. The Company’s performance obligations under the license agreements may include the transfer of intellectual property rights in the form of licenses, obligations to provide research and development services and related materials and participation on certain development and/or commercialization committees. Revenue is recognized when, or as, performance obligations are satisfied, which occurs when control of the promised products or services is transferred to customers. Revenue is measured as the amount of consideration the Company expects to receive in exchange for transferring products or services to a customer (“transaction price”). To the extent that the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price utilizing the most likely amount method. Variable consideration is included in the transaction price if, in the Company’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Estimates of variable consideration and determination of whether to include estimated amounts in the transaction price are based largely on an assessment of the Company’s anticipated performance and all information (historical, current and forecasted) that is reasonably available. The Company assesses the promises to determine if they are distinct performance obligations. Once the performance obligations are determined, the transaction price is allocated based on a relative standalone selling price basis. Milestone payments and royalties are typically considered variable consideration at the outset of the contract and are recognized in the transaction price either upon occurrence or when the constraint of a probable reversal is no longer applicable. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. Arrangements containing licenses to the Company’s intellectual property typically provide for a know-how transfer period. These arrangements may or may not also include rights to future updates of that intellectual property and related know-how. Revenues from non-refundable, up-front fees allocated to the licenses are recognized as the license is transferred to the customer and the customer is able to use and benefit from the license. This generally takes place over the related know-how transfer period, or if applicable, over the term of transfer of future updates to the intellectual property. Development Milestone Payments: At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license fees and earnings in the period of adjustment. For development milestones related to the KKC Agreement, the Company does not take a substantive role or control the research, development or commercialization of any products generated by KKC. Therefore, the Company is not able to reasonably estimate when, if at all, any development milestone payments may be payable to the Company. As such, the development milestone payments associated with the KKC Agreement involve a substantial degree of uncertainty and risk that they may never be received. Commercial Milestone Payments and Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of commercial sales, and the license is deemed to be the predominant item to which the royalties or commercial milestones relate, the Company will recognize revenue at the later of when the related sales occur or when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date no commercial milestone payments or royalties have been achieved. When no performance obligations are required of the Company, or following the completion of the performance obligation period, such amounts are recognized as revenue upon transfer of control of the goods or services to the customer. Generally, all amounts received or due other than sales-based milestones and royalties are classified as license fees. Sales-based milestones and royalties will be recognized as royalty revenue at the later of when the related sales occur or when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). Deferred revenue arises from amounts received in advance of the culmination of the earnings process and is recognized as revenue in future periods as performance obligations are satisfied. Deferred revenue expected to be recognized within the next twelve months is classified as a current liability. Upfront payment contract liabilities resulting from the Company’s license agreements do not represent a financing component as the payment is not financing the transfer of goods or services, and the technology underlying the licenses granted reflects research and development expenses already incurred by the Company.
Research and Development	Research and Development Research and development costs are expensed as incurred. Research and development expenses include payroll and personnel expenses, consulting costs, external contract research and development expenses, and allocated overhead, including rent, equipment depreciation, and utilities. Research and development costs that are paid in advance of performance are capitalized as a prepaid expense and amortized over the service period as the services are provided. The Company expenses upfront license payments related to acquired technologies that have not yet reached technological feasibility and have no alternative future use. In instances where the Company enters into cost-sharing arrangements, all research and development costs reimbursed by the collaborators are accounted for as reductions to research and development expense. During the year ended December 31, 2019, the Company incurred $2.0 million in external costs related to cost-sharing collaborations, of which $1.0 million has been recorded as a reduction to research and development expense. During the year ended December 31, 2018, the Company incurred $4.7 million in external costs related to cost-sharing collaborations, of which $2.4 million has been recorded as a reduction to research and development expense. During the year ended December 31, 2017, the Company incurred $3.0 million in external costs related to cost-sharing collaborations, of which $1.4 million has been recorded as a reduction to research and development expense.
Clinical Trial Costs	Clinical Trial Costs Clinical trial costs are a component of research and development expenses. The Company accrues and expenses clinical trial activities performed by third parties based on an evaluation of the progress to completion of specific tasks using data such as patient enrollment, clinical site activations, or other information provided to us by our vendors.
Income Taxes	Income Taxes The Company records deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax bases of assets and liabilities and for loss and credit carryforwards using enacted tax rates expected to be in effect in the years in which the differences reverse. A valuation allowance is provided to reduce the net deferred tax assets to the amount that will more likely than not be realized. The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more likely than not that a position will be sustained, none of the benefit attributable to the position is recognized. The tax benefit to be recognized for any tax position that meets the more-likely-than-not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency. The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes.
Guarantees and Indemnifications	Guarantees and Indemnifications As permitted under Delaware law, the Company indemnifies its officers, directors, and employees for certain events or occurrences that happen by reason of the relationship with, or position held at, the Company. The Company has standard indemnification arrangements under office leases (as described in Note 14) that require it to indemnify the landlord against all costs, expenses, fines, suits, claims, demands, liabilities, and actions directly resulting from any breach, violation, or nonperformance of any covenant or condition of the Company’s lease. Through December 31, 2019, the Company had not experienced any losses related to these indemnification obligations and no claims were outstanding. The Company does not expect significant claims related to these indemnification obligations, and consequently, concluded that the fair value of these obligations is negligible, and no related reserves were established.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for all stock option awards granted to employees and non-employees using a fair value method. Stock-based compensation is measured at the grant date fair value of the stock option grants and is recognized over the requisite service period of the awards (usually the vesting period) on a straight-line basis. For equity awards that have a performance condition, the Company recognizes compensation expense based on its assessment of the probability that the performance condition will be achieved. The Company accounts for forfeitures as they occur.
Recently Issued and Adopted Accounting Pronouncements	Recently Issued and 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 ASC 842) using the prospective method, effective on January 1, 2019. See Note 5 “Leases” to our consolidated financial statements included elsewhere herein 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 consolidated balance sheet, consolidated statement of comprehensive loss or consolidated statement of cash flows.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

3. Summary of Significant Accounting Policies

Use of Estimates

The preparation of 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 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.

Cash Equivalents

Cash equivalents include all highly liquid investments maturing within 90 days or less from the date of purchase. Cash equivalents include money market funds, corporate debt securities, U.S. government agency notes, and overnight deposits.

Restricted Cash

The Company classifies as restricted cash all cash pledged as collateral to secure long-term obligations and all cash whose use is otherwise limited by contractual provisions. Amounts are reported as non-current unless restrictions are expected to be released in the next 12 months.

Short-Term Investments

Short-term investments include marketable securities with maturities of less than one year or where management’s intent is to use the investments to fund current operations or to make them available for current operations. Long-term investments include marketable securities with remaining maturities greater than one year or that are due after one year from the balance sheet date. All investments in marketable securities are classified as available-for-sale and are reported at fair value with unrealized gains and losses excluded from earnings and reported net of tax in accumulated other comprehensive income, which is a component of stockholders’ equity (deficit). Unrealized losses that are determined to be other-than-temporary, based on current and expected market conditions, are recognized in earnings. Declines in fair value determined to be credit related are charged to earnings. The cost of marketable securities sold is determined by the specific identification method.

Segment Reporting

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision-making group, in making decisions regarding resource allocation and assessing performance. The Company has one operating segment.

Concentrations of Credit Risk

Cash and cash equivalents, restricted cash, and short-term and long-term investments are financial instruments that potentially subject the Company to concentrations of credit risk. Substantially all of the Company’s cash, cash equivalents, and short-term investments were deposited in accounts at two financial institutions, and at times, such deposits may exceed federally insured limits. The Company has not experienced any losses in such accounts, and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. The Company’s available-for-sale investments primarily consist of government money market funds, corporate debt securities, commercial paper, credit card asset-backed securities and overnight deposits and potentially subject the Company to concentrations of credit risk.

Property and Equipment

Property and equipment are recorded at cost. Depreciation is recorded using the straight-line method over the estimated useful lives of the assets (three to five years). Assets under capital leases are amortized over the shorter of their useful lives or lease term using the straight-line method. Major replacements and improvements are capitalized, while general repairs and maintenance are expensed as incurred.

Impairment of Long-Lived Assets

Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. When such events occur, the Company compares the carrying amounts of the assets to their undiscounted expected future cash flows. If this comparison indicates that there is impairment, the amount of impairment is calculated as the difference between the carrying value and fair value. To date, no such impairments have been recognized.

Revenue Recognition

The Company adopted Accounting Standards Codification (“ASC”) Rule 606 Revenue from Contracts with Customers (ASC 606), on January 1, 2018, using the modified retrospective method for all contracts not completed as of the date of adoption. The reported results for 2018 reflect the application of ASC 606 guidance while the reported results for 2017 were prepared under the guidance of ASC 605, Revenue Recognition (ASC 605). As of January 1, 2018, the Company had only one contract within the scope of ASC 606, a license agreement with Kyowa Kirin Co., Ltd. (“KKC”), under which the Company granted KKC an exclusive license to develop and commercialize entinostat in Japan and Korea (the “KKC License Agreement”). The KKC License Agreement is discussed further in Note 4.

The Company enters into license agreements for the development and commercialization of its product candidates. License agreements may include non-refundable upfront payments, contingent payments based on the occurrence of specified events under the Company’s license arrangements, partial or complete reimbursement of research and development expenses, license fees and royalties on sales of entinostat if they are successfully approved and commercialized. The Company’s performance obligations under the license agreements may include the transfer of intellectual property rights in the form of licenses, obligations to provide research and development services and related materials and participation on certain development and/or commercialization committees.

Revenue is recognized when, or as, performance obligations are satisfied, which occurs when control of the promised products or services is transferred to customers. Revenue is measured as the amount of consideration the Company expects to receive in exchange for transferring products or services to a customer (“transaction price”). To the extent that the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price utilizing the most likely amount method. Variable consideration is included in the transaction price if, in the Company’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Estimates of variable consideration and determination of whether to include estimated amounts in the transaction price are based largely on an assessment of the Company’s anticipated performance and all information (historical, current and forecasted) that is reasonably available.

The Company assesses the promises to determine if they are distinct performance obligations. Once the performance obligations are determined, the transaction price is allocated based on a relative standalone selling price basis. Milestone payments and royalties are typically considered variable consideration at the outset of the contract and are recognized in the transaction price either upon occurrence or when the constraint of a probable reversal is no longer applicable.

Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. Arrangements containing licenses to the Company’s intellectual property typically provide for a know-how transfer period. These arrangements may or may not also include rights to future updates of that intellectual property and related know-how. Revenues from non-refundable, up-front fees allocated to the licenses are recognized as the license is transferred to the customer and the customer is able to use and benefit from the license. This generally takes place over the related know-how transfer period, or if applicable, over the term of transfer of future updates to the intellectual property.

Development Milestone Payments: At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license fees and earnings in the period of adjustment. For development milestones related to the KKC Agreement, the Company does not take a substantive role or control the research, development or commercialization of any products generated by KKC. Therefore, the Company is not able to reasonably estimate when, if at all, any development milestone payments may be payable to the Company. As such, the development milestone payments associated with the KKC Agreement involve a substantial degree of uncertainty and risk that they may never be received.

Commercial Milestone Payments and Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of commercial sales, and the license is deemed to be the predominant item to which the royalties or commercial milestones relate, the Company will recognize revenue at the later of when the related sales occur or when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date no commercial milestone payments or royalties have been achieved.

When no performance obligations are required of the Company, or following the completion of the performance obligation period, such amounts are recognized as revenue upon transfer of control of the goods or services to the customer. Generally, all amounts received or due other than sales-based milestones and royalties are classified as license fees. Sales-based milestones and royalties will be recognized as royalty revenue at the later of when the related sales occur or when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied).

Deferred revenue arises from amounts received in advance of the culmination of the earnings process and is recognized as revenue in future periods as performance obligations are satisfied. Deferred revenue expected to be recognized within the next twelve months is classified as a current liability. Upfront payment contract liabilities resulting from the Company’s license agreements do not represent a financing component as the payment is not financing the transfer of goods or services, and the technology underlying the licenses granted reflects research and development expenses already incurred by the Company.

Research and Development

Research and development costs are expensed as incurred. Research and development expenses include payroll and personnel expenses, consulting costs, external contract research and development expenses, and allocated overhead, including rent, equipment depreciation, and utilities. Research and development costs that are paid in advance of performance are capitalized as a prepaid expense and amortized over the service period as the services are provided. The Company expenses upfront license payments related to acquired technologies that have not yet reached technological feasibility and have no alternative future use.

In instances where the Company enters into cost-sharing arrangements, all research and development costs reimbursed by the collaborators are accounted for as reductions to research and development expense. During the year ended December 31, 2019, the Company incurred $2.0 million in external costs related to cost-sharing collaborations, of which $1.0 million has been recorded as a reduction to research and development expense. During the year ended December 31, 2018, the Company incurred $4.7 million in external costs related to cost-sharing collaborations, of which $2.4 million has been recorded as a reduction to research and development expense. During the year ended December 31, 2017, the Company incurred $3.0 million in external costs related to cost-sharing collaborations, of which $1.4 million has been recorded as a reduction to research and development expense.

Clinical Trial Costs

Clinical trial costs are a component of research and development expenses. The Company accrues and expenses clinical trial activities performed by third parties based on an evaluation of the progress to completion of specific tasks using data such as patient enrollment, clinical site activations, or other information provided to us by our vendors.

Income Taxes

The Company records deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax bases of assets and liabilities and for loss and credit carryforwards using enacted tax rates expected to be in effect in the years in which the differences reverse. A valuation allowance is provided to reduce the net deferred tax assets to the amount that will more likely than not be realized. The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more likely than not that a position will be sustained, none of the benefit attributable to the position is recognized. The tax benefit to be recognized for any tax position that meets the more-likely-than-not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency. The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes.

Guarantees and Indemnifications

As permitted under Delaware law, the Company indemnifies its officers, directors, and employees for certain events or occurrences that happen by reason of the relationship with, or position held at, the Company. The Company has standard indemnification arrangements under office leases (as described in Note 14) that require it to indemnify the landlord against all costs, expenses, fines, suits, claims, demands, liabilities, and actions directly resulting from any breach, violation, or nonperformance of any covenant or condition of the Company’s lease. Through December 31, 2019, the Company had not experienced any losses related to these indemnification obligations and no claims were outstanding. The Company does not expect significant claims related to these indemnification obligations, and consequently, concluded that the fair value of these obligations is negligible, and no related reserves were established.

Stock-Based Compensation

The Company accounts for all stock option awards granted to employees and non-employees using a fair value method. Stock-based compensation is measured at the grant date fair value of the stock option grants and is recognized over the requisite service period of the awards (usually the vesting period) on a straight-line basis. For equity awards that have a performance condition, the Company recognizes compensation expense based on its assessment of the probability that the performance condition will be achieved. The Company accounts for forfeitures as they occur.

Recently Issued and 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 ASC 842) using the prospective method, effective on January 1, 2019. See Note 5 “Leases” to our consolidated financial statements included elsewhere herein 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 consolidated balance sheet, consolidated statement of comprehensive loss or consolidated statement of cash flows.

Stock-Based Compensation - Additional Information (Detail) - USD ($)		1 Months Ended	12 Months Ended
	Jan. 01, 2019	Sep. 30, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance			16,595,598
Share-based compensation, stock options granted			1,964,025
Share-based compensation, stock options vested			5,655,008
Share-based compensation, stock options cancelled			134,140
Weighted-average grant date fair value of options granted			$ 4.81	$ 6.17	$ 6.68
Stock options exercised, shares			25,857	7,850	46,680
Stock options exercised			$ 178,000	$ 26,000	$ 277,000
Intrinsic value of options exercised			9,000	100,000	200,000
Share based compensation expense, total			6,005,000	6,201,000	5,450,000
Contributions by the company			119,000	126,000	106,000
Performance Based Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to stock option			$ 700,000
Share-based compensation, stock options granted			60,000
Share-based compensation, stock options vested			13,333
Share-based compensation, stock options cancelled			6,667
Stock compensation expense			$ 88,000	142,000	$ 29,000
Service Based Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to stock option			$ 9,400,000
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance			1,750,000
Shares available for issuance			586,554
Common stock outstanding					4.00%
2015 Plan [Member] \| Subsequent Event [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance						1,672,173
2007 and 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to stock option			$ 10,100,000
Weighted average period to recognize compensation expense			2 years 3 months 18 days
2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense			$ 181,000
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 employees			583,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued under plan			42,818
Periodic payroll deductions offering periods	6 months
Offering period discount rate	15.00%
Share based compensation expense, total			$ 113,000	$ 132,000	$ 42,000
Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance	1,128,398
Shares authorized for issuance		250,000

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2016	$ 84,139	$ 2	$ 389,374	$ 56	$ (305,293)
Beginning balance, Shares at Dec. 31, 2016		18,215,181
Proceeds from follow on offering, net of offering cost of $3,665	48,675		48,675
Proceeds from follow on offering, net of offering cost of $3,665, Shares		3,950,190
Proceeds from exercise of stock options	$ 277		277
Proceeds from exercise of stock options, Shares	46,680	46,680
Vesting of restricted stock, Value	$ 59		59
Vesting of restricted stock, Shares		8,543
Stock-based compensation expense	5,450		5,450
Proceeds from "At-the-market" offering, net, Value	1,705		1,705
Proceeds from "At-the-market" offering, net, Shares		148,421
Unrealized gains (losses) on short-term investments	(199)			(199)
Employee withholdings ESPP	97		97
Cumulative effect adjustment of adoption ASU \| ASU 2016-09 [Member]			16		(16)
Proceeds from direct stock placement, net, Value	24,918		24,918
Proceeds from direct stock placement, net, Shares		2,021,018
Net loss	(60,802)				(60,802)
Ending balance at Dec. 31, 2017	104,319	$ 2	470,571	(143)	(366,111)
Ending balance, Shares at Dec. 31, 2017		24,390,033
Proceeds from exercise of stock options	$ 26		26
Proceeds from exercise of stock options, Shares	7,850	7,850
Stock-based compensation expense	$ 6,201		6,201
Proceeds from "At-the-market" offering, net, Value	15,497		15,497
Proceeds from "At-the-market" offering, net, Shares		2,114,169
Stock purchase under ESPP, Shares		24,684
Unrealized gains (losses) on short-term investments	118			118
Employee withholdings ESPP	198		198
Cumulative effect adjustment of adoption ASU \| ASU 2014-09 [Member]	649				649
Retirement of common stock in exchange for common stock warrant	(16,780)		(16,780)
Retirement of common stock in exchange for common stock warrant, shares		(2,000,000)
Issuance of common stock warrant in exchange for retirement of common stock	16,780		16,780
Net loss	(73,961)				(73,961)
Ending balance at Dec. 31, 2018	53,047	$ 2	492,493	(25)	(439,423)
Ending balance, Shares at Dec. 31, 2018		24,835,951
Stock issuance due to warrant exercise, cashless, Shares		299,215
Proceeds from exercise of stock options	$ 178		178
Proceeds from exercise of stock options, Shares	25,857	25,857
Stock-based compensation expense	$ 6,005		6,005
Proceeds from "At-the-market" offering, net, Value	830		830
Proceeds from "At-the-market" offering, net, Shares		140,819
Proceeds from direct offering, net, value	10,902	$ 1	10,901
Proceeds from direct offering,net, Shares		2,095,039
Proceeds from pre-funded common stock warrant from direct offering, net, value	13,032		13,032
Issuance of common stock warrant with direct offering, value	3,446		3,446
Stock purchase under ESPP, Shares		42,818
Unrealized gains (losses) on short-term investments	25			$ 25
Employee withholdings ESPP	182		182
Net loss	(56,047)				(56,047)
Ending balance at Dec. 31, 2019	$ 31,600	$ 3	$ 527,067		$ (495,470)
Ending balance, Shares at Dec. 31, 2019		27,140,484

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 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 (in thousands):

			Fair Value Measurements Using
	Total Carrying Value		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
December 31, 2019
Assets:
Cash equivalents	$	24,609	$	23,439	$	1,170	$	—
Short-term investments		35,166		—		35,166		—
Total assets	$	59,775	$	23,439	$	36,336	$	—
December 31, 2018
Assets:
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 (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2019
Commercial paper	$	15,675	$	5	$	—		$	15,680
Corporate bonds		18,361		—		(5	)		18,356
Asset back securities		2,300		—		—			2,300
	$	36,336	$	5	$	(5	)	$	36,336
December 31, 2018
Commercial paper	$	22,619	$	—	$	(15	)	$	22,604
Corporate bonds		29,047		2		(12	)		29,037
	$	51,666	$	2	$	(27	)	$	51,641

Leases - Additional Information (Detail)			12 Months Ended
Leases - Additional Information (Detail)	Sep. 30, 2016 ft²	Dec. 31, 2015 ft²	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Lessee Lease Description [Line Items]
Right-of-use asset, net			$ 716,000	$ 1,300,000
Lease liability			$ 897,000	$ 1,300,000
Lease option to extend			true
Lease option to termination			true
Operating lease discount rate			14.00%
Operating lease expense			$ 447,000
Lease payments			566,000
Future minimum lease payments under capital leases			$ 9,000		$ 14,000
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. 01, 2017
Remaining lease term			26 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. 01, 2016
Remaining lease term			14 months

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 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

	Years Ended December 31,
	2019		2018		2017
Research and development	$	2,061	$	1,910	$	1,363
General and administrative		3,944		4,291		4,087
Total	$	6,005	$	6,201	$	5,450

Grant Date Fair Values of Options Issued to Employees and Non-employees Estimated Using Black-Scholes Option Pricing Model

The grant date fair values of options issued to employees and non-employees were estimated using the Black-Scholes option-pricing model with the following assumptions:

	Years Ended December 31,
	2019			2018			2017
Expected term (in years)		5.97			5.90			6.02
Volatility rate		76.95	%		76.28	%		73.86	%
Risk-free interest rate		2.29	%		2.69	%		2.02	%
Expected dividend yield		0.00	%		0.00	%		0.00	%

Summary of Employee and Non-Employee Option Activity

A summary of employee and non-employee option activity under the Company’s equity award plans is presented below (in thousands, except share data):

	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding—January 1, 2019		4,252,983		$	9.23		7.3	$	66
Granted		1,964,025		$	6.99
Exercised		(25,857	)	$	6.86
Canceled or forfeited		(134,140	)	$	9.85
Outstanding—December 31, 2019		6,057,011		$	8.50		7.2	$	6,306
Exercisable—December 31, 2019		3,620,626		$	8.93		6.1	$	3,114
Options vested, exercisable or expected to vest—December 31, 2019		5,655,008		$	8.64		7.1	$	5,373

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Net tax provision	$ 0	$ 0
Increase (decrease) in valuation allowance	$ 12,800,000	17,200,000
Valuation allowance for deferred tax assets, description	The Company has provided a valuation allowance for the full amount of the net deferred tax assets as the realization of the deferred tax assets is not determined to be more likely than not. The valuation allowance increased by $12.8 million and $17.2 million in 2019 and 2018, respectively, due to the increase in deferred tax assets, primarily due to net operating loss carryforwards and capitalized research and development costs.
Federal net operating losses	$ 68,000,000
State net operating losses	$ 33,100,000
Operating loss carryforward expiration period	2025
Internal Revenue Service [Member]
Income Taxes [Line Items]
Uncertain tax positions	$ 200,000	200,000
Interest or penalties recorded during the period	0	$ 0
Unrecognized income tax benefits that would affect effective tax rate	0
Federal [Member]
Income Taxes [Line Items]
Deferred tax assets research credits	$ 2,900,000
Deferred tax assets research credits expiration period	2021
State [Member]
Income Taxes [Line Items]
Deferred tax assets research credits	$ 1,600,000
Deferred tax assets research credits expiration period	2021

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Components of Deferred Tax

The significant components of the Company’s deferred tax are as follows (in thousands):

	Years Ended December 31,
	2019			2018
Deferred tax assets (liabilities):
Net operating loss carryforwards	$	16,410		$	12,684
Research and development credits		4,156			3,443
Capitalized start-up and research and development costs, net		55,452			59,331
Deferred revenue		3,334			3,690
Depreciation and amortization of capitalized cost		13			(11,550	)
Accruals		828			630
Other temporary differences		4,223			3,423
Deferred tax assets before valuation allowance		84,416			71,651
Valuation allowances		(84,416	)		(71,651	)
Net deferred tax assets	$	—		$	—

Summary of Reconciliation of Company's Unrecognized Tax Benefits

A reconciliation of the Company’s unrecognized tax benefits is as follows (in thousands):

	Years Ended December 31,
	2019		2018		2017
Unrecognized tax benefit--beginning of year	$	163	$	163	$	241
Decreases related to prior period positions		—		—		(78	)
Unrecognized tax benefit--end of year	$	163	$	163	$	163

Subsequent Events - Additional Information (Details) - USD ($)				1 Months Ended
	Oct. 01, 2020	Feb. 07, 2020	Jan. 30, 2020	Jan. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Common stock, par value						$ 0.0001	$ 0.0001	$ 0.0001
Gross proceeds from offering					$ 27,600,000
Hercules [Member] \| Loan Agreement [Member] \| Scenario Forecast [Member]
Subsequent Event [Line Items]
Minimum cash covenant	$ 12,500,000
Default interest rate	5.00%
Subsequent Event [Member]
Subsequent Event [Line Items]
Issuance and sale of shares of common stock				3,036,719
Common stock, par value				$ 0.0001
Gross proceeds from offering			$ 35,000,000
Subsequent Event [Member] \| Hercules [Member] \| Loan Agreement [Member]
Subsequent Event [Line Items]
Aggregate maximum borrowings		$ 30,000,000
Interest rate description		Borrowings under the Loan Agreement bear interest at an annual rate equal to the greater of (i) 9.85% or (ii) 5.10% plus the Wall Street Journal prime rate.
Maturity date		Sep. 01, 2023
Percentage of prepayment premium of principal amount outstanding in first year		2.00%
Percentage of prepayment premium of principal amount outstanding in second year		1.50%
Percentage of prepayment premium of principal amount outstanding thereafter prior to maturity date		1.00%
Facility charge paid		$ 100,000
Subsequent Event [Member] \| Hercules [Member] \| Loan Agreement [Member] \| Performance Milestone [Member]
Subsequent Event [Line Items]
Maturity date		Mar. 01, 2024
Subsequent Event [Member] \| Hercules [Member] \| Loan Agreement [Member] \| Wall Street Journal Prime Rate [Member]
Subsequent Event [Line Items]
Basis spread on variable rate		5.10%
Subsequent Event [Member] \| Hercules [Member] \| Loan Agreement [Member] \| Minimum [Member]
Subsequent Event [Line Items]
Interest rate limit		9.85%
Subsequent Event [Member] \| Hercules [Member] \| Loan Agreement [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Percentage of repayment on aggregate principal amount of term loan advances		4.99%
Subsequent Event [Member] \| Hercules [Member] \| Loan Agreement [Member] \| Term Loan [Member]
Subsequent Event [Line Items]
Term loan		$ 20,000,000
Subsequent Event [Member] \| Hercules [Member] \| Loan Agreement [Member] \| Additional Term Loan [Member]
Subsequent Event [Line Items]
Term loan		10,000,000
Subsequent Event [Member] \| Hercules [Member] \| Loan Agreement [Member] \| Tranche 2 [Member]
Subsequent Event [Line Items]
Facility charge paid		$ 50,000
Securities Purchase Agreement [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Issuance and sale of shares of common stock			3,036,719
Common stock, par value			$ 0.0001
Pre-Funded Warrants [Member]
Subsequent Event [Line Items]
Warrants issued (in shares)					2,500,000
Warrant exercise price per share					$ 0.0001
Offering price					$ 5.9999
Pre-Funded Warrants [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Warrants issued (in shares)				1,338,287
Offering price			$ 7.9999	$ 7.9999
Pre-Funded Warrants [Member] \| Securities Purchase Agreement [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Warrants issued (in shares)			1,338,287
Warrant exercise price per share			$ 0.0001
Series Warrants [Member]
Subsequent Event [Line Items]
Warrants issued (in shares)					4,595,039	4,595,039
Offering price					$ 6.00
Series Warrants [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Offering price			8.00	8.00
Series One Warrants [Member]
Subsequent Event [Line Items]
Warrant exercise price per share						$ 12.00
Series One Warrants [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Warrant exercise price per share			10.00
Series One Warrants [Member] \| Subsequent Event [Member] \| Minimum [Member]
Subsequent Event [Line Items]
Warrant exercise price per share				10.00
Series One Warrants [Member] \| Subsequent Event [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Warrant exercise price per share				12.00
Series Two Warrants [Member]
Subsequent Event [Line Items]
Warrant exercise price per share						$ 18.00
Series Two Warrants [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Warrant exercise price per share			$ 13.00
Series Two Warrants [Member] \| Subsequent Event [Member] \| Minimum [Member]
Subsequent Event [Line Items]
Warrant exercise price per share				13.00
Series Two Warrants [Member] \| Subsequent Event [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Warrant exercise price per share				$ 18.00

Net Loss per Share Attributable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 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 (in thousands, except per share data):

	Years Ended December 31,
	2019			2018			2017
Numerator--basic and diluted:
Net loss	$	(56,047	)	$	(73,961	)	$	(60,802	)
Net loss attributable to common stockholders--basic and diluted	$	(56,047	)	$	(73,961	)	$	(60,802	)
Net loss per share—basic and diluted	$	(1.84	)	$	(2.92	)	$	(2.90	)
Denominator—basic and diluted:
Weighted-average common shares used to compute net loss per share—basic and diluted		30,490,783			25,371,511			20,997,211

Potential Dilutive Securities Excluded from Computation of Diluted Net Loss per Common Share

	December 31,
	2019		2018		2017
Options to purchase common stock		6,057,011		4,252,983		3,391,832
Common stock warrants		4,595,039		—		357,840
ESPP shares		15,223		29,736		—

Property and Equipment, Net - Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 591	$ 608
Accumulated depreciation	(310)	(235)
Property and equipment, net	281	373
Office and Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	21	38
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	134	134
Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	256	256
Office Equipment Under Capital Lease [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	13	13
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 167	$ 167

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Short-term deposits	$ 1,297	$ 663
Prepaid clinical supplies	166	101
Interest receivable on investments	116	253
Reimbursable costs	416	797
Prepaid insurance	214	188
Other	347	332
Total prepaid expenses and other current assets	$ 2,556	$ 2,334

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued professional fees	$ 403	$ 484
Accrued compensation and related costs	2,800	2,804
Accrued clinical costs	6,726	9,726
Other	266	135
Total accrued expenses	$ 10,195	$ 13,149

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Stockholders Equity [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Follow on offering cost			$ 3,665
At-the-market, offering expenses	$ 34	$ 67
Direct offering, common stock warrants			1,571
Direct offering, offering expenses			98
Pre-funded common stock warrants			1,875
Pre-funded common stock warrants offering expenses			$ 93

Stock-Based Compensation - Grant Date Fair Values of Options Issued to Employees and Non-employees Estimated Using Black-Scholes Option Pricing Model (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]
Expected term (in years)	5 years 11 months 19 days	5 years 10 months 24 days	6 years 7 days
Volatility rate	76.95%	76.28%	73.86%
Risk-free interest rate	2.29%	2.69%	2.02%
Expected dividend yield	0.00%	0.00%	0.00%

Fair Value Measurements - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 36,336	$ 51,666
Unrealized Gains	5	2
Unrealized Losses	(5)	(27)
Fair Value	36,336	51,641
Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	15,675	22,619
Unrealized Gains	5
Unrealized Losses		(15)
Fair Value	15,680	22,604
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	18,361	29,047
Unrealized Gains		2
Unrealized Losses	(5)	(12)
Fair Value	18,356	$ 29,037
Asset Back Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,300
Fair Value	$ 2,300

Supplemental Cash Flow Information - Supplemental disclosures of cash flow (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Supplemental Disclosures of Non-Cash Investing and Financing Activities:
Issuance costs included in accounts payable and accrued expenses	$ 50
Vesting of restricted stock	$ 59

Supplemental Cash Flow Information - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Supplemental Cash Flow Information [Abstract]
Right-of-use asset	$ 716	$ 1,300
Lease liability	$ 897	$ 1,300

Fair Value Measurements - Schedule of Fair Values of Financial Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 35,166	$ 47,142
Carrying Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	24,609	33,769
Short-term investments	35,166	47,142
Total assets	59,775	80,911
Quoted Prices in Active Markets Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	23,439	29,270
Total assets	23,439	29,270
Significant Other Observable Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	1,170	4,499
Short-term investments	35,166	47,142
Total assets	$ 36,336	$ 51,641

Common Stock - Schedule of Common Stock Reserved for Future Issuance (Detail)	Dec. 31, 2019 shares
Class Of Stock [Line Items]
Common stock reserved for future issuance	16,595,598
Pre-Funded Warrants [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	4,500,000
Series 1 and 2 Warrants [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	4,595,039
Options to Purchase Common Stock [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	6,643,565
Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	856,994

Net Loss per Share Attributable to Common Stockholders - Additional Information (Detail) - Pre-Funded Warrants [Member] - $ / shares		1 Months Ended
	Jun. 18, 2018	Mar. 31, 2019
Earnings Per Share Basic [Line Items]
Warrant issued		2,500,000
Warrant exercise price per share		$ 0.0001
Biotechnology Value Fund, L.P. [Member]
Earnings Per Share Basic [Line Items]
Number of common stock converted to warrants	2,000,000
Number of common stock warrants issued	2,000,000
Warrant exercise price per share	$ 0.0001

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 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 outstanding	27,140,484	24,835,951

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019 USD ($) Segment Claim	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments \| Segment	1
Impairment charge	$ 0
Guarantees and Indemnifications [Member]
Summary Of Significant Accounting Policies [Line Items]
Indemnification obligations, claims outstanding \| Claim	0
Indemnification obligations claims, reserves established	$ 0
Cost-Sharing Collaborations [Member]
Summary Of Significant Accounting Policies [Line Items]
External costs related to cost-sharing collaborations	2,000,000	$ 4,700,000	$ 3,000,000
Cost-sharing collaborations recorded as a reduction to research and development expense	$ 1,000,000	$ 2,400,000	$ 1,400,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	three years
Percentage of income tax contingency realized	50.00%
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	five years

Commitments - Additional Information (Detail) $ in Millions	Apr. 30, 2013 USD ($)
Eddingpharm Purchase Agreement [Member]
Commitment And Contingencies [Line Items]
Purchase agreement obligation	$ 5.0

Fair Value Measurements - Additional Information (Detail) - USD ($)	36 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value Measurements [Line Items]
Available for sale debt securities fair value	$ 36,336,000	$ 51,641,000
Realized gains or losses recognized on the sale or maturity of available-for-sale securities	0
Quoted Prices in Active Markets Level 1 [Member]
Fair Value Measurements [Line Items]
Cash equivalents fair value	23,439,000	29,270,000
Quoted Prices 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	23,400,000	29,300,000
Significant Other Observable Inputs Level 2 [Member]
Fair Value Measurements [Line Items]
Cash equivalents fair value	1,170,000	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	1,200,000	4,500,000
Significant Other Observable Inputs Level 2 [Member] \| Corporate Bonds and Commercial Paper [Member] \| Short-term Investments [Member]
Fair Value Measurements [Line Items]
Available for sale debt securities fair value	$ 35,200,000	$ 47,100,000

Leases - Summary of Future Minimum Lease Payments under Operating Leases (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Operating Lease Liabilities Payments Due [Abstract]
2019			$ 569
2020	$ 585		588
2021	394		395
2022	59		59
Total lease payments	1,038		$ 1,611
Less: imputed interest	(141)
Total operating lease liability	$ 897	$ 1,300