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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	May 06, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Trading Symbol	SNDX
Entity Registrant Name	SYNDAX PHARMACEUTICALS INC
Entity Central Index Key	0001395937
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		36,094,929
Entity Shell Company	false
Title of 12(b) Security	Common Stock
Security Exchange Name	NASDAQ
Entity File Number	001-37708
Entity Incorporation, State or Country Code	DE
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
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 44,629	$ 24,609
Restricted cash	115
Short-term investments	54,376	35,166
Prepaid expenses and other current assets	5,086	2,556
Total current assets	104,206	62,331
Property and equipment, net	259	281
Right-of-use asset, net	608	716
Other assets	82	197
Total assets	105,155	63,525
Current liabilities:
Accounts payable	8,998	6,178
Accrued expenses and other current liabilities	7,795	10,195
Current portion of deferred revenue	1,517	1,517
Current portion of right-of-use liability	480	478
Total current liabilities	18,790	18,368
Long-term liabilities:
Deferred revenue, less current portion	12,754	13,133
Right-of-use liability, less current portion	306	419
Loan payable	19,792
Other long-term liabilities	4	5
Total long-term liabilities	32,856	13,557
Total liabilities	51,646	31,925
Commitments
Stockholders’ equity:
Preferred stock, $0.001 par value, 10,000,000 shares authorized; 0 shares outstanding at March 31, 2020 and December 31, 2019
Common stock, $0.0001 par value, 100,000,000 shares authorized; 30,240,838 and 27,140,484 shares issued and outstanding at March 31, 2020 and December 31, 2019, respectively	3	3
Additional paid-in capital	564,164	527,067
Accumulated other comprehensive income	48
Accumulated deficit	(510,706)	(495,470)
Total stockholders’ equity	53,509	31,600
Total liabilities and stockholders’ equity	$ 105,155	$ 63,525

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	30,240,838	27,140,484
Common stock, shares outstanding	30,240,838	27,140,484

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue:
Total revenues	$ 379	$ 379
Type of revenue [extensible list]		us-gaap:LicenseMember
Operating expenses:
Research and development	9,562	$ 11,279
General and administrative	5,917	3,911
Total operating expenses	15,479	15,190
Loss from operations	(15,100)	(14,811)
Other (expense) income:
Interest expense	(449)
Interest income	333	452
Other (expense) income	(20)	57
Total other (expense) income	(136)	509
Net loss	(15,236)	(14,302)
Other comprehensive income (loss):
Unrealized gain on marketable securities	48	33
Comprehensive loss	(15,188)	(14,269)
Net loss attributable to common stockholders	$ (19,142)	$ (14,302)
Net loss per share attributable to common stockholders—basic and diluted	$ (0.56)	$ (0.53)
Weighted-average number of common shares used to compute net loss per share attributable to common stockholders—basic and diluted	34,328,640	27,023,466

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (15,236,000)	$ (14,302,000)
Adjustments to reconcile net loss to net cash from operating activities:
Depreciation	23,000	(180,000)
Amortization and accretion of investments	(110,000)
Non-cash operating lease expense	108,000
Non-cash interest expense	62,000
Stock-based compensation	1,829,000	1,592,000
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(2,530,000)	(2,453,000)
Accounts payable	2,820,000	2,908,000
Deferred revenue	(379,000)	(379,000)
Accrued expenses and other liabilities	(2,512,000)	(4,017,000)
Net cash used in operating activities	(15,925,000)	(16,831,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of short-term investments	(34,938,000)	(20,628,000)
Proceeds from sales and maturities of short-term investments	15,885,000	33,380,000
Net cash (used in) provided by investing activities	(19,053,000)	12,752,000
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from debt agreement, net	19,730,000
Proceeds from Employee Stock Purchase Plan	64,000	27,000
Proceeds from stock option exercises	338,000
Other		(2,000)
Net cash provided by financing activities	54,998,000	28,426,000
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	20,020,000	24,347,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH—beginning of period	24,724,000	33,985,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH —end of period	44,744,000	58,332,000
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid for interest	126,000
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Issuance costs debt included in accounts payable and accrued expenses	82,000	171,000
At-the-Market Offering [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net		830,000
Private Placement [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net	$ 34,866,000	$ 27,571,000

Nature of Business

3 Months Ended

Mar. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Business

1. Nature of Business

Syndax Pharmaceuticals, Inc. (“we,” “us,” “our” or the “Company”) is a clinical stage biopharmaceutical company developing an innovative pipeline of cancer therapies. We were incorporated in Delaware in 2005. We base our operations in Waltham, Massachusetts and we operate in one segment.

Basis of Presentation

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Basis of Presentation

2. Basis of Presentation

The Company has prepared the accompanying condensed consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. The interim unaudited condensed financial statements have been prepared on the same basis as the annual audited financial statements and in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of March 31, 2020, and the results of operations and comprehensive loss for the three months ended March 31, 2020 and 2019, and cash flows for the three months ended March 31, 2020 and 2019. The results for the three months ended March 31, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020, any other interim periods, or any future year or period. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2019, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K that was filed with the Securities and Exchange Commission (“SEC”) on March 5, 2020.

In 2011, the Company established a wholly owned subsidiary in the United Kingdom. There have been no activities for this entity to date. In 2014, the Company established a wholly owned U.S. subsidiary, Syndax Securities Corporation. The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

3. Summary of Significant Accounting Policies

Significant Accounting Policies

The Company’s significant accounting policies, which are disclosed in the audited consolidated financial statements for the year ended December 31, 2019 and the notes thereto are included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 5, 2020. Since the date of that filing, there have been no material changes to the Company’s significant accounting policies except as noted below.

Significant Risks and Uncertainties

With the global spread of the ongoing COVID-19 pandemic in the first and second quarters of 2020, we have implemented business continuity plans designed to address and mitigate the impact of the COVID-19 pandemic on our business. We anticipate that the COVID-19 pandemic could have an impact on the clinical development timelines for one or more of our clinical programs. The extent to which the COVID-19 pandemic impacts our business, our clinical development, manufacturing of clinical and commercial drug substance and drug product, and regulatory efforts, our corporate development objectives and the value of and market for our common stock, will depend on future developments that are highly uncertain and cannot be predicted with confidence at this time, such as the ultimate duration of the pandemic, travel restrictions, quarantines, social distancing and business closure requirements in the U.S., Europe and other countries, and the effectiveness of actions taken globally to contain and treat the disease. The global economic slowdown, the overall disruption of global healthcare systems and the other risks and uncertainties associated with the pandemic could have a material adverse effect on our business, financial condition, results of operations and growth prospects.

In addition, we are subject to other challenges and risks specific to our business and our ability to execute on our strategy, as well as risks and uncertainties common to companies in the pharmaceutical industry with development and commercial operations, including, without limitation, risks and uncertainties associated with: obtaining regulatory approval of our late-stage product candidate; delays or problems in the supply of our products, loss of single source suppliers or failure to comply with manufacturing regulations; identifying, acquiring or in-licensing additional products or product candidates; pharmaceutical product development and the inherent uncertainty of clinical success; and the challenges of protecting and enhancing our intellectual property rights; complying with applicable regulatory requirements. In addition, to the extent the ongoing COVID-19 pandemic adversely affects our business and results of operations, it may also have the effect of heightening many of the other risks and uncertainties discussed above.

Debt Issuance Cost

Debt issuance costs consist of payments made to secure commitments under certain debt financing arrangements. These amounts are recognized as interest expense over the period of the financing arrangement using the effective interest method. If the financing arrangement is canceled or forfeited, or if the utility of the arrangement to the Company is otherwise compromised, these costs are recognized as interest expense immediately. The Company’s consolidated financial statements present debt issuance costs related to a recognized debt liability as a direct reduction from the carrying amount of that debt liability.

Derivative Financial Instruments

The Company accounts for derivative financial instruments as either equity or liabilities in accordance with Accounting Standards Codification Topic 815, Derivatives and Hedging, based on the characteristics and provisions of each instrument. Embedded derivatives are required to be bifurcated from the host instruments and recorded at fair value if the derivatives are not clearly and closely related to the host instruments on issuance date. The Company did not have any material embedded derivatives that required bifurcation upon issuance or as of March 31, 2020.

Use of Estimates

The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of costs and expenses during the reporting period. The Company bases estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. The Company evaluates its estimates and assumptions on an ongoing basis. The Company’s actual results may differ from these estimates under different assumptions or conditions.

We anticipate that the COVID-19 pandemic will have an impact on the clinical and pre-clinical development timelines for our clinical and pre-clinical programs. Estimates and assumptions about future events and their effects cannot be determined with certainty and therefore require the exercise of judgment. As of the date of issuance of these financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, assumptions and judgments or revise the carrying value of its assets or liabilities. These estimates may change as new events occur and additional information is obtained and are recognized in the consolidated financial statements as soon as they become known. Actual results could differ from those estimates and any such differences may be material to the Company’s financial statements.

Revenue from Contracts with Customers

3 Months Ended

Mar. 31, 2020

Revenue From Contract With Customer [Abstract]

Revenue from Contracts with Customers

4. Revenue from Contracts with Customers

On December 19, 2014 (the “Effective Date”), the Company entered into a license agreement with Kyowa Kirin, Co., Ltd. (the KKC License Agreement), under which the Company granted KKC an exclusive license to develop and commercialize entinostat in Japan and Korea. Under the terms of the KKC License Agreement, the Company will be responsible for the manufacture and supply of the products during the development activities. In addition to the license and manufacturing obligations, the Company is obligated to provide KKC access to know-how and regulatory information the Company may develop over the life of the entinostat patent. Lastly, to the extent additional intellectual property is developed during the term of the agreement, KKC will receive the right to the intellectual property when and if available. KKC will conduct the development, regulatory approval filings, and commercialization activities of entinostat in Japan and Korea. KKC paid the Company $25.0 million upfront, which included a $7.5 million equity investment and a $17.5 million non-refundable cash payment. In addition, to the extent certain development and commercial milestones are achieved, KKC will be required to pay the Company up to $75.0 million in milestone payments over the term of the license agreement. The term of the agreement commenced on the Effective Date and, unless earlier terminated in accordance with the terms of the agreement, will continue on a country-by-country and product-by-product basis, until the later of: (i) the date all valid claims of the last effective patent among the Company’s patents expires or is abandoned, withheld, or is otherwise invalidated in such country; and (ii) 15 years from the date of the first commercial sale of a product in the Japan or Korea.

The equity purchase and the up-front payment of the license fee were accounted for separately. The Company allocated the amount of consideration equal to the fair value of the shares on the Effective Date, which resulted in $7.7 million of proceeds allocated to the equity purchase and the remaining consideration of $17.3 million allocated to the up-front license fee.

In October 2017, the Company announced that KKC enrolled the first Japanese patient into a local pivotal study of entinostat for the treatment of hormone receptor positive, human epidermal growth factor receptor 2 negative breast cancer. In accordance with the terms of the license agreement, KKC paid the Company a $5.0 million milestone payment which the Company received in December 2017.

The Company determined that the performance obligations associated with the KKC License Agreement include (i) the combined license, rights to access and use materials and data, and rights to additional intellectual property, and (ii) the clinical supply obligation. All other goods or services promised to KHK are immaterial in the context of the agreement. Under ASC 606, the identification of the clinical supply obligation as a distinct performance obligation separate and apart from the license performance obligation resulted in a change in the performance period. The start of the performance period under ASC 606 was determined to be the contract inception date, December 19, 2014. The clinical supply was identified as a separate performance obligation under ASC 606 as (i) the Company is not providing a significant service of integration whereby the clinical supply and other promises are inputs into a combined output, (ii) the clinical supply does not significantly modify or customize the other promises nor is it significantly modified or customized by them, and (iii) the clinical supply is not highly interdependent or highly interrelated with the other promises in the agreement as KKC could choose not to purchase the clinical supply from the Company without significantly affecting the other promised goods or services. The Company further concluded that the clinical supply represented an immaterial performance obligation and therefore the entire $17.3 million allocated to the upfront payment was allocated to the combined license and will be recognized ratably over the performance period, representing contract inception though 2029. In 2017, KKC achieved a development milestone, and was required to pay the Company $5.0 million. The Company is recognizing the development milestone consideration over the performance period coinciding with the license to intellectual property. As the Company determined that its performance obligations associated with the KKC Agreement at contract inception were not distinct and represented a single performance obligation, and that the obligations for goods and services provided would be completed over the performance period of the agreement, any payments received by the Company from KKC, including the upfront payment and progress-dependent development and regulatory milestone payments, are recognized as revenue using a time-based proportional performance model over the contract term (December 2014 through 2029) of the collaboration, within license fees. To date no commercial milestone payments or royalties have been achieved.

Contract liabilities consisted of deferred revenue, as presented on the consolidated balance sheet, as of March 31, 2020. Deferred revenue related to the KHK License Agreement was $14.3 million as of March 31, 2020 and will be recognized over the remainder of the contract term.

Net Loss per Share Attributable to Common Stockholders

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

Net Loss per Share Attributable to Common Stockholders

5. Net Loss per Share Attributable to Common Stockholders

Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period. Because the Company has reported a net loss for all periods presented, diluted net loss per common share is the same as basic net loss per common share for those periods. The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company:

	Three Months Ended March 31,
	2020			2019
	(In thousands, except share and per share data)
Numerator—basic and diluted:
Net loss	$	(15,236	)	$	(14,302	)
Deemed dividend due to warrant reset		(3,906	)		—
Net loss attributable to common stockholders—basic and diluted	$	(19,142	)	$	(14,302	)
Net loss per share attributable to common stockholders—basic and diluted	$	(0.56	)	$	(0.53	)
Denominator—basic and diluted:
Weighted-average number of common shares used to compute net loss per share attributable to common stockholders—basic and diluted		34,328,640			27,023,466

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):

	March 31,
	2020		2019
Options to purchase common stock		6,897,802		5,629,120
Warrants to purchase common stock		4,595,039		4,595,039
Employee Stock Purchase Plan		24,214		27,471
Non-vested restricted stock units (RSUs)		15,000		—

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 warrants. Further, as discussed in Note 13, in March 2019, the Company sold 2,095,039 shares of common stock as well as 2,500,000 pre-funded warrants and 4,595,039 Series 1 and Series 2 warrants. The pre-funded warrants are exercisable into shares of common stock for $0.0001 per share. In January 2020, the Company sold 3,036,719 shares of common stock as well as 1,338,287 pre-funded warrants. The 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.

Significant Agreements

3 Months Ended

Mar. 31, 2020

Equity [Abstract]

Significant Agreements

6. Significant Agreements

Vitae Pharmaceuticals, Inc.

In October 2017, the Company entered into a license agreement (the “Allergan License Agreement”) with Vitae Pharmaceuticals, Inc., a subsidiary of Allergan plc (“Allergan”), under which Allergan granted the Company an exclusive, sublicensable, worldwide license to a portfolio of preclinical, orally available, small molecule inhibitors of the interaction of Menin with the Mixed Lineage Leukemia (“MLL”) protein (the “Menin Assets”). The Company made a nonrefundable upfront payment of $5.0 million to Allergan in the fourth quarter of 2017. Additionally, subject to the achievement of certain milestone events, the Company may be required to pay Allergan up to $99.0 million in one-time development and regulatory milestone payments over the term of the Allergan License Agreement. In the event that the Company or any of its affiliates or sublicensees commercializes the Menin Assets, the Company will also be obligated to pay Allergan low single to low double-digit royalties on sales, subject to reduction in certain circumstances, as well as up to an aggregate of $70.0 million in potential one-time, sales-based milestone payments based on achievement of certain annual sales thresholds. Under certain circumstances, the Company may be required to share a percentage of non-royalty income from sublicensees, subject to certain deductions, with Allergan. The Company is solely responsible for the development and commercialization of the Menin Assets. Each party may terminate the Allergan License Agreement for the other party’s uncured material breach or insolvency; and the Company may terminate the Allergan License Agreement at will at any time upon advance written notice to Allergan. Allergan may terminate the Allergan License Agreement if the Company or any of its affiliates or sublicensees institutes a legal challenge to the validity, enforceability, or patentability of the licensed patent rights. Unless terminated earlier in accordance with its terms, the Allergan License Agreement will continue on a country-by-country and product-by-product basis until the later of: (i) the expiration of all of the licensed patent rights in such country; (ii) the expiration of all regulatory exclusivity applicable to the product in such country; and (iii) 10 years from the date of the first commercial sale of the product in such country. As of the date of the Allergan License Agreement, the asset acquired had no alternative future use nor had it reached a stage of technological feasibility. As the processes or activities that were acquired along with the license do not constitute a “business,” the transaction has been accounted for as an asset acquisition. In June 2019, the Company achieved certain development and regulatory milestones. As a result, in June 2019, the Company recorded $4.0 million as research and development expense. The $4.0 million payable has been recorded in accounts payable as of March 31, 2020.

UCB Biopharma Sprl

In 2016, the Company entered into a license agreement (the “UCB License Agreement”) with UCB Biopharma Sprl (“UCB”), under which UCB granted to the Company a worldwide, sublicenseable, exclusive license to UCB6352, which the Company refers to as axatilimab, an investigational new drug (“IND”) ready anti-CSF-1R monoclonal antibody. The Company made a nonrefundable upfront payment of $5.0 million to UCB in 2016. Additionally, subject to the achievement of certain milestone events, the Company may be required to pay UCB up to $119.5 million in one-time development and regulatory milestone payments over the term of the UCB License Agreement. In the event that the Company or any of its affiliates or sublicensees commercializes axatilimab, the Company will also be obligated to pay UCB low double-digit royalties on sales, subject to reduction in certain circumstances, as well as up to an aggregate of $250.0 million in potential one-time, sales-based milestone payments based on achievement of certain annual sales thresholds. Under certain circumstances, the Company may be required to share a percentage of non-royalty income from sublicensees, subject to certain deductions, with UCB. The Company is solely responsible for the development and commercialization of axatilimab, except that UCB is performing a limited set of transitional chemistry, manufacturing and control tasks related to axatilimab. 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.

Eastern Cooperative Oncology Group

In March 2014, the Company entered into the ECOG Agreement with Eastern Cooperative Oncology Group, a contracting entity for the Eastern Cooperative Oncology Group—American College of Radiology Imaging Network Cancer Research Group (“ECOG-ACRIN”), that describes the parties’ obligations with respect to the NCI-sponsored pivotal Phase 3 clinical trial of entinostat. Under the terms of the ECOG Agreement, ECOG-ACRIN will perform this clinical trial in accordance with the clinical trial protocol and a mutually agreed scope of work. The Company is providing a fixed level of financial support for the clinical trial through an upfront payment of $0.7 million and a series of payments of up to $1.0 million each that are comprised of milestone payments through the completion of enrollment and time-based payments through the completion of patient monitoring post-enrollment. In addition, the Company is obligated to supply entinostat and placebo to ECOG-ACRIN for use in the clinical trial. From the second quarter of 2016 through the fourth quarter of 2018, we have 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. We have agreed to provide this additional financial support to fund the additional activities required to ensure that the E2112 clinical trial will satisfy FDA registration requirements. As of March 31, 2020, the Company’s aggregate payment obligations under this agreement are approximately $24.6 million; and its remaining payment obligations are approximately $5.8 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 U.S. Food and Drug Administration (“FDA”) or National Cancer Institute (“NCI”) withdraws the authorization to perform the clinical trial in the United States. The parties may jointly terminate the ECOG Agreement if the parties agree that safety-related issues support termination of the clinical trial. The Company records the appropriate clinical trial expenses in its financial statements by matching those expenses with the period in which the services and efforts are expended. The Company accounts for these expenses according to the progress of the clinical trial as measured by patient enrollment and the timing of various aspects of the clinical trial. The Company determines accrual estimates through financial models, taking into account discussion with applicable personnel and ECOG-ACRIN as to the progress or state of consummation of the clinical trial or the services completed.

Bayer Pharma AG (formerly known as Bayer Schering Pharma AG)

In March 2007, the Company entered into a license agreement (the “Bayer Agreement”) with Bayer Schering Pharma AG (“Bayer”) for a worldwide, exclusive license to develop and commercialize entinostat and any other products containing the same active ingredient. Under the terms of the Bayer Agreement, the Company paid a nonrefundable upfront license fee of $2.0 million and is responsible for the development and marketing of entinostat. The Company recorded the $2.0 million license fee as research and development expense during the year ended December 31, 2007, as it had no alternative future use. The Company will pay Bayer royalties on a sliding scale based on net sales, if any, and make future milestone payments to Bayer of up to $150.0 million in the event that certain specified development and regulatory goals and sales levels are achieved.

Fair Value Measurements

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

7. Fair Value Measurements

The carrying amounts of cash and cash equivalents, restricted cash, accounts payable, and accrued expenses approximated their estimated fair values due to the short-term nature of these financial instruments. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value are performed in a manner to maximize the use of observable inputs and minimize the use of unobservable inputs. The accounting standard describes a fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value, which are the following:

Level 1—

Quoted prices (unadjusted) in active markets that are accessible at the market date for identical unrestricted assets or liabilities.

Level 2—

Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs for which all significant inputs are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3—

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

During the periods presented, the Company has not changed the manner in which it values assets and liabilities that are measured at fair value using Level 3 inputs. The Company recognizes transfers between levels of the fair value hierarchy as of the end of the reporting period. There were no transfers within the hierarchy for any of periods presented.

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

	Fair Value Measurements Using
			Quoted
			Prices		Significant
			(unadjusted)		Other		Significant
	Total		in Active		Observable		Unobservable
	Carrying		Markets		Inputs		Inputs
	Value		(Level 1)		(Level 2)		(Level 3)
	(In thousands)
March 31, 2020
Assets:
Cash and cash equivalents	$	44,629	$	44,629	$	—	$	—
Short-term investments		54,376		—		54,376		—
Total assets	$	99,005	$	44,629	$	54,376	$	—
December 31, 2019
Assets:
Cash and cash equivalents	$	24,609	$	23,439	$	1,170	$	—
Short-term investments		35,166		—		35,166		—
Total assets	$	59,775	$	23,439	$	36,336	$	—

Cash and cash equivalents of $44.6 million and $23.4 million as of March 31, 2020 and December 31, 2019, respectively, consisted of overnight investments and money market funds and are classified within Level 1 of the fair value hierarchy because they are valued using quoted market prices in active markets. Cash equivalents of $1.2 million as of December 31, 2019, 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 $54.4 million and $35.2 million as of March 31, 2020 and December 31, 2019, respectively, consisted of commercial paper, highly rated corporate bonds and asset backed securities and are classified within Level 2 of the fair value hierarchy because pricing inputs are other than quoted prices in active markets, which are either directly or indirectly observable as of the reporting date, and fair value is determined through the use of models or other valuation methodologies.

The short-term investments are classified as available-for-sale securities. As of March 31, 2020, the remaining contractual maturities of the available-for-sale securities were less than one year, and the balance in the Company’s accumulated other comprehensive income was comprised solely of activity related to the Company’s available-for-sale securities. There were no realized gains or losses recognized on the sale or maturity of available-for-sale securities during the three months ended March 31, 2020 and 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 March 31, 2020, which the Company does not intend to sell and has concluded it will not be required to sell before recovery of the amortized cost for the investment at maturity. The following table summarizes the available-for-sale securities:

	Amortized		Unrealized		Unrealized
	Cost		Gains		Losses			Fair Value
	(In thousands)
March 31, 2020
Commercial paper	$	36,987	$	85	$	—		$	37,072
Corporate bonds		15,041		1		(38	)		15,004
Asset-backed securities		2,300		—		—			2,300
	$	54,328	$	86	$	(38	)	$	54,376
December 31, 2019
Commercial paper	$	15,675	$	5	$	—		$	15,680
Corporate bonds		18,361		—		(5	)		18,356
Asset-backed securities		2,300		—		—			2,300
	$	36,336	$	5	$	(5	)	$	36,336

Prepaid Expenses and Other Current Assets

3 Months Ended

Mar. 31, 2020

Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]

Prepaid Expenses and Other Current Assets

8. Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following:

	March 31, 2020		December 31, 2019
	(In thousands)
Short-term deposits	$	2,343	$	1,297
Prepaid clinical supplies		152		166
Interest receivable on investments		167		116
Reimbursable costs		324		416
Prepaid insurance		1,693		214
Other		407		347
Total prepaid expenses and other current assets	$	5,086	$	2,556

Accrued Expenses and Other Current Liabilities

3 Months Ended

Mar. 31, 2020

Payables And Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

9. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

	March 31, 2020		December 31, 2019
	(In thousands)
Accrued professional fees	$	373	$	403
Accrued compensation and related costs		1,223		2,800
Accrued clinical costs		5,664		6,726
Other		535		266
Total accrued expenses and other current liabilities	$	7,795	$	10,195

Stock-Based Compensation

3 Months Ended

Mar. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

10. Stock-Based Compensation

In January 2020, the number of shares of common stock available for issuance under the 2015 Omnibus Incentive Plan (“2015 Plan”), was increased by 1,085,619 shares due to the automatic annual provision to increase shares available under the 2015 Plan. As of March 31, 2020, the total number of shares of common stock available for issuance under the 2015 Plan was 765,348. The Company recognized stock-based compensation expense related to the issuance of stock option awards to employees and non-employees and related to the 2015 Employee Stock Purchase Plan (“ESPP”) in the condensed consolidated statements of comprehensive loss as follows:

	Three Months Ended March 31,
	2020		2019
	(In thousands)
Research and development	$	532	$	534
General and administrative		1,297		1,058
Total	$	1,829	$	1,592

Compensation expense by type of award in the three months ended March 31, 2020 and 2019 was as follows:

	Three Months Ended March 31,
	2020		2019
	(In thousands)
Stock options	$	1,793	$	1,559
Employee Stock Purchase Plan		36		33
Total	$	1,829	$	1,592

During the three months ended March 31, 2020, the Company granted 1,121,825 stock options to certain executives and employees having service-based vesting conditions. The grant date fair value of the options granted in the three months ended March 31, 2020, was $7.3 million, or $6.52 per share on a weighted-average basis and will be recognized as compensation expense over the requisite service period of three to four years.

In 2019, the Company granted 583,000 stock options to certain employees to purchase shares of common stock that contain certain performance-based vesting criteria, primarily related to the achievement of certain clinical and regulatory development milestones related to product candidates. Recognition of stock-based compensation expense associated with these performance-based stock options commences when the performance condition is considered probable of achievement, using management’s best estimates, which consider the inherent risk and uncertainty regarding the future outcomes of the milestones.

The achievement of one of the performance milestones was considered to be probable and the Company recorded approximately $50,000 of stock compensation expense associated with these awards for the three months ended March 31, 2020. One performance milestone was not achieved by December 31, 2019, and therefore 194,338 stock options were cancelled on January 1, 2020. For the remaining award containing performance-based vesting criteria, the achievement of the milestone was considered not probable, nor met, and therefore no expense has been recognized related to this award for the three months ended March 31, 2020.

During the three months ended March 31, 2020, 51,034 options were exercised for cash proceeds of $338,000. No options were exercised in the three months ended March 31, 2019.

As of March 31, 2020, there was $15.6 million of unrecognized compensation cost related to employee and non-employee unvested stock options granted under the 2015 and 2007 Plans, which is expected to be recognized over a weighted-average remaining service period of 2.7 years. Stock compensation costs have not been capitalized by the Company.

Restricted stock units

During the three months ended March 31, 2020, the Company granted 15,000 shares of the Company’s restricted stock units. The shares are scheduled to vest in equal annual tranches over a four-year period on the anniversary date of the related grant. The fair value of these shares totaled $142,000 at the grant date, representing a weighted-average grant date fair value per share of $9.47.

Employee Stock Purchase Plan

3 Months Ended

Mar. 31, 2020

Postemployment Benefits [Abstract]

Employee Stock Purchase Plan

11. Employee Stock Purchase Plan

In January 2020, the number of shares of common stock available for issuance under the ESPP, was increased by 271,404 shares as a result of the automatic increase provision of the ESPP. As of March 31, 2020, the total number of shares of common stock available for issuance under the ESPP was 1,115,797. The Company issued 12,601 shares during the first three months of 2020.

The ESPP is considered a compensatory plan with the related compensation cost expensed over the six-month offering period starting on February 1 and on August 1. The compensation expense related to the ESPP for the three months ended March 31, 2020, was approximately $36,000. The compensation expense related to the ESPP recorded in the three months ended March 31, 2019, was approximately $33,000.

Loan Payable

3 Months Ended

Mar. 31, 2020

Debt Disclosure [Abstract]

Loan Payable

12. Loan Payable

In February 2020, the Company entered into a loan and security agreement (the “Loan Agreement”) with Hercules Capital, Inc. (“Hercules”), which provided for aggregate maximum borrowings of up to $30.0 million, consisting of (i) a term loan of up to $20.0 million, which was funded on February 7, 2020 (the “Initial Advance”), and (ii) subject to Hercules’ investment committee approval, an additional term loan of up to $10.0 million, available for borrowing from February 7, 2020 to December 15, 2020 (the “Tranche 2 Advance”). 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. As of March 31, 2020, the Company’s interest rate under the Loan Agreement was 9.85%.

Borrowings under the Loan Agreement are repayable in monthly interest-only payments through October 1, 2021, or April 1, 2022 if the Phase 3 clinical trial of entinostat (E2112) in patients with advanced hormone receptor positive, human epidermal growth factor receptor 2 negative, breast cancer has achieved the primary efficacy endpoint sufficient to file an NDA as the next step in clinical development (“Performance Milestone”). After the interest-only payment period, borrowings under the Loan Agreement are repayable in equal monthly payments of principal and accrued interest until the maturity date of the loan, which is either (i) September 1, 2023, or (ii) March 1, 2024 upon achievement of the Performance Milestone (the “Maturity Date”). At the Company’s option, the Company may prepay all, but not less than all, of the outstanding borrowings, subject to a prepayment premium equal to (i) 2.0% of the principal amount outstanding if the prepayment occurs during the first year following the applicable loan being funded, (ii) 1.5% of the principal amount outstanding if the prepayment occurs during the second year following the applicable loan being funded, and (iii) 1.0% of the principal amount outstanding at any time thereafter but prior to the Maturity Date. In addition, the Company paid a $100,000 facility charge upon closing, which is being expensed over the term of the debt, and will pay a $50,000 facility charge in connection with the Tranche 2 Advance. The Loan Agreement also provides for a final payment, payable upon maturity or the repayment in full of all obligations under the agreement, of up to 4.99% of the aggregate principal amount of the Term Loan Advances (as defined in the Loan Agreement). The final payment will be accrued over the term of the debt.

Borrowings under the Loan Agreement are collateralized by substantially all of the Company’s and its subsidiaries personal property and other assets, other than its intellectual property. The Loan Agreement includes a minimum cash covenant of $12.5 million that applies commencing on October 1, 2020, subject to reduction upon satisfaction of certain conditions as set forth in the Loan Agreement. In addition, the Loan Agreement includes customary affirmative and restrictive covenants and representations and warranties, including a covenant against the occurrence of a “change in control,” financial reporting obligations, and certain limitations on indebtedness, liens (including a negative pledge on intellectual property and other assets), investments, distributions (including dividends), collateral, investments, distributions, transfers, mergers or acquisitions, taxes, corporate changes, and deposit accounts. The Loan Agreement also includes customary events of default, including payment defaults, breaches of covenants following any applicable cure period, the occurrence of certain events that could reasonably be expected to have a “material adverse effect” as set forth in the Loan Agreement, cross acceleration to third-party indebtedness and certain events relating to bankruptcy or insolvency. Upon the occurrence of an event of default, a default interest rate of an additional 5.0% may be applied to the outstanding principal balance, and Hercules may declare all outstanding obligations immediately due and payable and take such other actions as set forth in the Loan Agreement.

In connection with the Loan Agreement, the Company was required to enter into separate deposit account control agreements with the lender in order to perfect the lender’s security interest in the cash collateral in the Company’s operating accounts. In the event of a default under the Loan Agreement, the lender would have the right to take control of the operating accounts and restrict the Company’s access to the operating accounts and the funds therein.

During the quarter ended March 31, 2020, the Company recognized $0.4 million of interest expense related to the Initial Advance pursuant to the Loan Agreement.

As of March 31, 2020, the Company’s maturities of principal obligations under its long-term debt are as follows:

	Amount
Remainder of 2020	$	—
2021		3,057
2022		9,809
2023		7,134
Total principal outstanding		20,000
Unamortized final fee		49
Unamortized debt issuance costs		(257	)
Total	$	19,792

Stockholders' Equity

3 Months Ended

Mar. 31, 2020

Equity [Abstract]

Stockholders' Equity

13. Stockholders’ Equity

The following table presents the changes in stockholders’ equity for the three months ended March 31, 2020:

(In thousands, except share data)	Common Stock $0.0001 Par Value				Additional Paid-In Capital			Accumulated Other Comprehensive Income / (Loss)		Accumulated Deficit			Total Stockholders’ Equity
	Shares		Amount
Balance as of December 31, 2019		27,140,484	$	3	$	527,067		$	—	$	(495,470	)	$	31,600
Stock purchase under ESPP		12,601		—		—			—		—			—
Stock-based compensation expense		—		—		1,829			—		—			1,829
Proceeds from direct offering, net of $93 offering expenses		3,036,719		—		24,201			—		—			24,201
Proceeds from pre-funded common stock warrant from direct offering, net of $41 offering expenses		—		—		10,665			—		—			10,665
Deemed dividend from repricing Series 1 and 2 warrants		—		—		3,906			—		—			3,906
Repricing Series 1 and 2 warrants		—		—		(3,906	)		—		—			(3,906	)
Proceeds from exercise of stock options		51,034		—		338			—		—			338
Unrealized gains on short-term investments		—		—					48		—			48
Employee withholdings ESPP		—		—		64			—		—			64
Net loss		—		—		—			—		(15,236	)		(15,236	)
Balance as of March 31, 2020		30,240,838	$	3	$	564,164		$	48	$	(510,706	)	$	53,509

The following table presents the changes in stockholders’ equity for the three months ended March 31, 2019:

(In thousands, except share data)	Common Stock $0.0001 Par Value				Additional Paid-In Capital		Accumulated Other Comprehensive Income / (Loss)			Accumulated Deficit			Total Stockholders’ Equity
	Shares		Amount
Balance as of December 31, 2018		24,835,951	$	2	$	492,493	$	(25	)	$	(439,423	)	$	53,047
Stock purchase under ESPP		23,970		—		—		—			—			—
Proceeds from 'at-the-market' offering, net of $34 offering expenses		140,819		—		830		—			—			830
Stock-based compensation expense		—		—		1,592		—			—			1,592
Proceeds from direct offering, net of $1,571 in common stock warrants, $78 offering expenses		2,095,039		1		10,921		—			—			10,922
Proceeds from pre-funded common stock warrant from direct offering, net of $1,875 in common stock warrants, $93 offering expenses		—		—		13,032		—			—			13,032
Issuance of common stock warrant with direct offering		—		—		3,446		—			—			3,446
Unrealized gains on short-term investments		—		—		—		33			—			33
Employee withholdings ESPP		—		—		26		—			—			26
Net loss		—		—		—		—			(14,302	)		(14,302	)
Balance as of March 31, 2019		27,095,779	$	3	$	522,340	$	8		$	(453,725	)	$	68,626

In April 2017, the Company entered into a sales agreement with Cowen and Company, LLC (“Cowen”) under which the Company may issue and sell shares of our common stock having aggregate sales proceeds of up to $50.0 million from time to time through Cowen, acting as agent, in a series of one or more at-the-market (the “2017 ATM Program”) equity offerings. Cowen is not required to sell any specific amount, but acts as our sales agent using commercially reasonable efforts consistent with its normal trading and sales practices. The Company pays Cowen up to 3% of the gross proceeds from any common stock sold through this sales agreement. In the first quarter of 2019, the Company sold 140,819 shares of common stock under the 2017 ATM Program for net proceeds of $0.8 million.

In August 2019, the Company entered into a new sales agreement with 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 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. In the first quarter of 2020, and through May 6, 2020, the Company sold no additional shares of common stock under the ATM program.

In March 2019, the Company issued 2,095,039 shares of its common stock and pre-funded warrants to purchase 2,500,000 shares of common stock 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 (collectively, the “Series Warrants”). The offering price for the securities was $6.00 per share (or $5.9999 for each Pre-Funded Warrant). The aggregate gross proceeds to the Company from this offering were $27.6 million, excluding any proceeds the Company may receive upon exercise of the pre-funded warrants and Series Warrants and offering costs of $0.2 million. No underwriter or placement agent participated in the offering.

The Series Warrants are immediately exercisable. Each Series 1 Warrant has an initial exercise price of $12.00 per share of common stock and each Series 2 Warrant has an initial exercise price of $18.00 per share of common stock, in each case subject to certain adjustments. The Series Warrants expire on the earlier of (i) 90 days following the Company’s confirmation to holders of the Company’s release of positive data confirming the achievement of the specified primary endpoint of overall survival benefit in the E2112 clinical trial in breast cancer patients, or (ii) December 31, 2020.

If, prior to the expiration date of the Series Warrant, the Company sells additional capital stock or derivative securities convertible into or exercisable for capital stock, as defined, in one or more related transactions primarily for the purpose of raising capital at a Weighted-Average Price (as described below) below $12.00 per share, then the initial exercise price of the Series Warrants will be automatically reset upon exercise to an exercise price (the “Adjusted Exercise Price”) that is the midpoint between the initial exercise price and the lowest Weighted-Average Price per share at which the Company sells capital stock or derivative securities convertible into or exercisable for capital stock in a subsequent offering prior to the exercise date; provided, however, that the Adjusted Exercise Price will not be reduced below $6.00 per share. The Weighted-Average Price shall be calculated as the weighted-average common stock equivalent price of the equity securities sold in such transaction(s) (excluding any derivative securities with an exercise or conversion price that is above the closing sale price as of the time of pricing such offering(s)). In no event will the exercise price for the Series Warrants be adjusted more than once pursuant to this adjustment mechanism.

The 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 permit the holders to receive a fixed number of shares of common stock upon exercise. In addition, such warrants do not provide any guarantee of value or return. The Company valued the Series Warrants at issuance in March 2019 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.

In January 2020, the Company sold 3,036,719 shares of common stock, and pre-funded warrants to purchase 1,338,287 shares of common stock. The offering price for the securities was $8.00 per share of common stock or $7.9999 for each pre-funded warrant. As a result of this offering, the exercise price of Series 1 Warrants 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 Company recorded $3.9 million as a deemed dividend which represents the value transferred to the warrant holders due to the Series Warrant adjustment mechanism being triggered. The deemed dividend was recorded as both an increase and a decrease in Additional Paid-in-Capital and reduced net income available to common stockholders by the same amount. The key inputs to the valuation model included the weighted average volatility of 96.74% and the weighted average expected term of 0.4 years.

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:

	March 31, 2020
Common stock issuable under pre-funded warrants		5,838,287
Series 1 and 2 warrants		4,595,039
Options to purchase common stock		765,348
Employee Stock Purchase Plan		1,115,797

Related-Party Transactions

3 Months Ended

Mar. 31, 2020

Related-Party Transactions

14. Related-Party Transactions

The Company’s chief executive officer and member of the board of directors is also an Executive Partner at MPM Asset Management, LLC, which holds an investment in the Company’s common stock.

Subsequent Event

3 Months Ended

Mar. 31, 2020

Subsequent Events [Abstract]

Subsequent Event

15. Subsequent Event

In May 2020, the Company closed an underwritten public offering whereby the Company sold 5,555,556 shares of common stock at a price of $18.00 per share. The aggregate net proceeds received by the Company were $93.7 million, net of underwriting discounts and commissions and estimated offering expenses payable by the Company. The offering allows for an additional 833,333 shares to be issued pursuant to the underwriters’ exercise of their option to purchase additional shares of common stock.

Basis of Presentation (Policies)	3 Months Ended
Basis of Presentation (Policies)	Mar. 31, 2020
Accounting Policies [Abstract]
Principles of Consolidation	In 2011, the Company established a wholly owned subsidiary in the United Kingdom. There have been no activities for this entity to date. In 2014, the Company established a wholly owned U.S. subsidiary, Syndax Securities Corporation. The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Significant Accounting Policies	Significant Accounting Policies The Company’s significant accounting policies, which are disclosed in the audited consolidated financial statements for the year ended December 31, 2019 and the notes thereto are included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 5, 2020. Since the date of that filing, there have been no material changes to the Company’s significant accounting policies except as noted below.
Significant Risks and Uncertainties	Significant Risks and Uncertainties With the global spread of the ongoing COVID-19 pandemic in the first and second quarters of 2020, we have implemented business continuity plans designed to address and mitigate the impact of the COVID-19 pandemic on our business. We anticipate that the COVID-19 pandemic could have an impact on the clinical development timelines for one or more of our clinical programs. The extent to which the COVID-19 pandemic impacts our business, our clinical development, manufacturing of clinical and commercial drug substance and drug product, and regulatory efforts, our corporate development objectives and the value of and market for our common stock, will depend on future developments that are highly uncertain and cannot be predicted with confidence at this time, such as the ultimate duration of the pandemic, travel restrictions, quarantines, social distancing and business closure requirements in the U.S., Europe and other countries, and the effectiveness of actions taken globally to contain and treat the disease. The global economic slowdown, the overall disruption of global healthcare systems and the other risks and uncertainties associated with the pandemic could have a material adverse effect on our business, financial condition, results of operations and growth prospects. In addition, we are subject to other challenges and risks specific to our business and our ability to execute on our strategy, as well as risks and uncertainties common to companies in the pharmaceutical industry with development and commercial operations, including, without limitation, risks and uncertainties associated with: obtaining regulatory approval of our late-stage product candidate; delays or problems in the supply of our products, loss of single source suppliers or failure to comply with manufacturing regulations; identifying, acquiring or in-licensing additional products or product candidates; pharmaceutical product development and the inherent uncertainty of clinical success; and the challenges of protecting and enhancing our intellectual property rights; complying with applicable regulatory requirements. In addition, to the extent the ongoing COVID-19 pandemic adversely affects our business and results of operations, it may also have the effect of heightening many of the other risks and uncertainties discussed above.
Debt Issuance Cost	Debt Issuance Cost Debt issuance costs consist of payments made to secure commitments under certain debt financing arrangements. These amounts are recognized as interest expense over the period of the financing arrangement using the effective interest method. If the financing arrangement is canceled or forfeited, or if the utility of the arrangement to the Company is otherwise compromised, these costs are recognized as interest expense immediately. The Company’s consolidated financial statements present debt issuance costs related to a recognized debt liability as a direct reduction from the carrying amount of that debt liability.
Derivative Financial Instruments	Derivative Financial Instruments The Company accounts for derivative financial instruments as either equity or liabilities in accordance with Accounting Standards Codification Topic 815, Derivatives and Hedging, based on the characteristics and provisions of each instrument. Embedded derivatives are required to be bifurcated from the host instruments and recorded at fair value if the derivatives are not clearly and closely related to the host instruments on issuance date. The Company did not have any material embedded derivatives that required bifurcation upon issuance or as of March 31, 2020.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of costs and expenses during the reporting period. The Company bases estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. The Company evaluates its estimates and assumptions on an ongoing basis. The Company’s actual results may differ from these estimates under different assumptions or conditions. We anticipate that the COVID-19 pandemic will have an impact on the clinical and pre-clinical development timelines for our clinical and pre-clinical programs. Estimates and assumptions about future events and their effects cannot be determined with certainty and therefore require the exercise of judgment. As of the date of issuance of these financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, assumptions and judgments or revise the carrying value of its assets or liabilities. These estimates may change as new events occur and additional information is obtained and are recognized in the consolidated financial statements as soon as they become known. Actual results could differ from those estimates and any such differences may be material to the Company’s financial statements.

Net Loss per Share Attributable to Common Stockholders (Tables)

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders

The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company:

	Three Months Ended March 31,
	2020			2019
	(In thousands, except share and per share data)
Numerator—basic and diluted:
Net loss	$	(15,236	)	$	(14,302	)
Deemed dividend due to warrant reset		(3,906	)		—
Net loss attributable to common stockholders—basic and diluted	$	(19,142	)	$	(14,302	)
Net loss per share attributable to common stockholders—basic and diluted	$	(0.56	)	$	(0.53	)
Denominator—basic and diluted:
Weighted-average number of common shares used to compute net loss per share attributable to common stockholders—basic and diluted		34,328,640			27,023,466

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

	March 31,
	2020		2019
Options to purchase common stock		6,897,802		5,629,120
Warrants to purchase common stock		4,595,039		4,595,039
Employee Stock Purchase Plan		24,214		27,471
Non-vested restricted stock units (RSUs)		15,000		—

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of Fair Values of Financial Assets and Liabilities Measured at Fair Value

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

	Fair Value Measurements Using
			Quoted
			Prices		Significant
			(unadjusted)		Other		Significant
	Total		in Active		Observable		Unobservable
	Carrying		Markets		Inputs		Inputs
	Value		(Level 1)		(Level 2)		(Level 3)
	(In thousands)
March 31, 2020
Assets:
Cash and cash equivalents	$	44,629	$	44,629	$	—	$	—
Short-term investments		54,376		—		54,376		—
Total assets	$	99,005	$	44,629	$	54,376	$	—
December 31, 2019
Assets:
Cash and cash equivalents	$	24,609	$	23,439	$	1,170	$	—
Short-term investments		35,166		—		35,166		—
Total assets	$	59,775	$	23,439	$	36,336	$	—

Summary of Available-for-Sale Securities

The following table summarizes the available-for-sale securities:

	Amortized		Unrealized		Unrealized
	Cost		Gains		Losses			Fair Value
	(In thousands)
March 31, 2020
Commercial paper	$	36,987	$	85	$	—		$	37,072
Corporate bonds		15,041		1		(38	)		15,004
Asset-backed securities		2,300		—		—			2,300
	$	54,328	$	86	$	(38	)	$	54,376
December 31, 2019
Commercial paper	$	15,675	$	5	$	—		$	15,680
Corporate bonds		18,361		—		(5	)		18,356
Asset-backed securities		2,300		—		—			2,300
	$	36,336	$	5	$	(5	)	$	36,336

Prepaid Expenses and Other Current Assets (Tables)

3 Months Ended

Mar. 31, 2020

Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]

Schedule of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following:

	March 31, 2020		December 31, 2019
	(In thousands)
Short-term deposits	$	2,343	$	1,297
Prepaid clinical supplies		152		166
Interest receivable on investments		167		116
Reimbursable costs		324		416
Prepaid insurance		1,693		214
Other		407		347
Total prepaid expenses and other current assets	$	5,086	$	2,556

Accrued Expenses and Other Current Liabilities (Tables)

3 Months Ended

Mar. 31, 2020

Payables And Accruals [Abstract]

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

	March 31, 2020		December 31, 2019
	(In thousands)
Accrued professional fees	$	373	$	403
Accrued compensation and related costs		1,223		2,800
Accrued clinical costs		5,664		6,726
Other		535		266
Total accrued expenses and other current liabilities	$	7,795	$	10,195

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share Based Compensation Expense Related to Issuance of Stock Option Awards to Employees and Non Employees Related to Employee Stock Purchase Plan

The Company recognized stock-based compensation expense related to the issuance of stock option awards to employees and non-employees and related to the 2015 Employee Stock Purchase Plan (“ESPP”) in the condensed consolidated statements of comprehensive loss as follows:

	Three Months Ended March 31,
	2020		2019
	(In thousands)
Research and development	$	532	$	534
General and administrative		1,297		1,058
Total	$	1,829	$	1,592

Compensation Expense by Type of Award

Compensation expense by type of award in the three months ended March 31, 2020 and 2019 was as follows:

	Three Months Ended March 31,
	2020		2019
	(In thousands)
Stock options	$	1,793	$	1,559
Employee Stock Purchase Plan		36		33
Total	$	1,829	$	1,592

Loan Payable (Tables)

3 Months Ended

Mar. 31, 2020

Debt Disclosure [Abstract]

Summary of Maturities of Principal Obligations Under Long-term Debt

As of March 31, 2020, the Company’s maturities of principal obligations under its long-term debt are as follows:

	Amount
Remainder of 2020	$	—
2021		3,057
2022		9,809
2023		7,134
Total principal outstanding		20,000
Unamortized final fee		49
Unamortized debt issuance costs		(257	)
Total	$	19,792

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2020

Equity [Abstract]

Summary of Changes in Stockholders' Equity

The following table presents the changes in stockholders’ equity for the three months ended March 31, 2020:

(In thousands, except share data)	Common Stock $0.0001 Par Value				Additional Paid-In Capital			Accumulated Other Comprehensive Income / (Loss)		Accumulated Deficit			Total Stockholders’ Equity
	Shares		Amount
Balance as of December 31, 2019		27,140,484	$	3	$	527,067		$	—	$	(495,470	)	$	31,600
Stock purchase under ESPP		12,601		—		—			—		—			—
Stock-based compensation expense		—		—		1,829			—		—			1,829
Proceeds from direct offering, net of $93 offering expenses		3,036,719		—		24,201			—		—			24,201
Proceeds from pre-funded common stock warrant from direct offering, net of $41 offering expenses		—		—		10,665			—		—			10,665
Deemed dividend from repricing Series 1 and 2 warrants		—		—		3,906			—		—			3,906
Repricing Series 1 and 2 warrants		—		—		(3,906	)		—		—			(3,906	)
Proceeds from exercise of stock options		51,034		—		338			—		—			338
Unrealized gains on short-term investments		—		—					48		—			48
Employee withholdings ESPP		—		—		64			—		—			64
Net loss		—		—		—			—		(15,236	)		(15,236	)
Balance as of March 31, 2020		30,240,838	$	3	$	564,164		$	48	$	(510,706	)	$	53,509

The following table presents the changes in stockholders’ equity for the three months ended March 31, 2019:

(In thousands, except share data)	Common Stock $0.0001 Par Value				Additional Paid-In Capital		Accumulated Other Comprehensive Income / (Loss)			Accumulated Deficit			Total Stockholders’ Equity
	Shares		Amount
Balance as of December 31, 2018		24,835,951	$	2	$	492,493	$	(25	)	$	(439,423	)	$	53,047
Stock purchase under ESPP		23,970		—		—		—			—			—
Proceeds from 'at-the-market' offering, net of $34 offering expenses		140,819		—		830		—			—			830
Stock-based compensation expense		—		—		1,592		—			—			1,592
Proceeds from direct offering, net of $1,571 in common stock warrants, $78 offering expenses		2,095,039		1		10,921		—			—			10,922
Proceeds from pre-funded common stock warrant from direct offering, net of $1,875 in common stock warrants, $93 offering expenses		—		—		13,032		—			—			13,032
Issuance of common stock warrant with direct offering		—		—		3,446		—			—			3,446
Unrealized gains on short-term investments		—		—		—		33			—			33
Employee withholdings ESPP		—		—		26		—			—			26
Net loss		—		—		—		—			(14,302	)		(14,302	)
Balance as of March 31, 2019		27,095,779	$	3	$	522,340	$	8		$	(453,725	)	$	68,626

Schedule of Common Stock Reserved for Future Issuance

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:

	March 31, 2020
Common stock issuable under pre-funded warrants		5,838,287
Series 1 and 2 warrants		4,595,039
Options to purchase common stock		765,348
Employee Stock Purchase Plan		1,115,797

Nature of Business - Additional Information (Detail)	3 Months Ended
Nature of Business - Additional Information (Detail)	Mar. 31, 2020 Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segments	1
Date of incorporation	Oct. 11, 2005
State of incorporation	DE

Revenue from Contract with Customers - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended	12 Months Ended
	Oct. 31, 2017	Dec. 19, 2014	Mar. 31, 2020	Dec. 31, 2017	Dec. 31, 2019
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			$ 14,300,000
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

Net Loss per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Numerator—basic and diluted:
Net loss	$ (15,236)	$ (14,302)
Net loss attributable to common stockholders—basic and diluted	$ (19,142)	$ (14,302)
Net loss per share attributable to common stockholders—basic and diluted	$ (0.56)	$ (0.53)
Denominator—basic and diluted:
Weighted-average number of common shares used to compute net loss per share attributable to common stockholders—basic and diluted	34,328,640	27,023,466
Warrant [Member]
Numerator—basic and diluted:
Deemed dividend due to warrant reset	$ (3,906)

- Definition

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

+ References + Details

Net Loss per Share Attributable to Common Stockholders - Potential Dilutive Securities Excluded from Computation of Diluted Net Loss per Common Share (Detail) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per common share	6,897,802	5,629,120
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per common share	4,595,039	4,595,039
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per common share	24,214	27,471
RSUs [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per common share	15,000

Net Loss per Share Attributable to Common Stockholders - Additional Information (Detail) - $ / shares		1 Months Ended
	Jun. 18, 2018	Mar. 31, 2020	Jan. 31, 2020	Mar. 31, 2019
Earnings Per Share Basic [Line Items]
Common stock, new shares issued		2,095,039	3,036,719
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
Pre-Funded Warrants [Member]
Earnings Per Share Basic [Line Items]
Warrant exercise price per share		$ 0.0001	$ 0.0001	$ 0.0001
Warrant issued		2,500,000	1,338,287
Series 1 and Series 2 Warrants [Member]
Earnings Per Share Basic [Line Items]
Warrant issued		4,595,039

Significant Agreements - Additional Information (Detail) - USD ($)	1 Months Ended					3 Months Ended			12 Months Ended	30 Months Ended
	Jun. 30, 2019	Oct. 31, 2017	Mar. 31, 2014	Dec. 31, 2007	Mar. 31, 2007	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense						$ 9,562,000	$ 11,279,000
Accounts payable						8,998,000					$ 6,178,000
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] \| Milestone Liability [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts payable						4,000,000
Allergan License Agreement [Member] \| Vitae Pharmaceuticals Inc [Member] \| Accrued Milestone Expenses [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense	$ 4,000,000
UCB License Agreement [Member] \| UCB Biopharma [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront milestone payable									$ 5,000,000
Potential milestone payments to be made									119,500,000
Aggregate potential milestone payable									$ 250,000,000
License expiration year									10 years
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						24,600,000
Remaining contractual obligation						$ 5,800,000
Period of contractual obligation						2 years
License Agreement [Member] \| Bayer Pharma AG [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense				$ 2,000,000
Up-front license fee paid					$ 2,000,000
License Agreement [Member] \| Bayer Pharma AG [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate payment obligation					$ 150,000,000

Fair Value Measurements - Schedule of Fair Values of Financial Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 54,376	$ 35,166
Carrying Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	44,629	24,609
Short-term investments	54,376	35,166
Total assets	99,005	59,775
Quoted Prices (Unadjusted) in Active Markets Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	44,629	23,439
Total assets	44,629	23,439
Significant Other Observable Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents		1,170
Short-term investments	54,376	35,166
Total assets	$ 54,376	$ 36,336

Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Fair Value Measurements [Line Items]
Available for sale debt securities fair value	$ 54,376,000		$ 36,336,000
Realized gains or losses recognized on the sale or maturity of available-for-sale securities	0	$ 0
Quoted Prices (Unadjusted) in Active Markets Level 1 [Member]
Fair Value Measurements [Line Items]
Cash and cash equivalents fair value	44,629,000		23,439,000
Quoted Prices (Unadjusted) in Active Markets Level 1 [Member] \| Overnight Investments, Money Market Funds and Highly Rated Corporate Bonds Member]
Fair Value Measurements [Line Items]
Cash and cash equivalents fair value	44,600,000		23,400,000
Significant Other Observable Inputs Level 2 [Member]
Fair Value Measurements [Line Items]
Cash and cash equivalents fair value			1,170,000
Significant Other Observable Inputs Level 2 [Member] \| Corporate Bonds and Commercial Paper [Member]
Fair Value Measurements [Line Items]
Cash and cash equivalents fair value			1,200,000
Significant Other Observable Inputs Level 2 [Member] \| Commercial Paper, Corporate Bonds and Asset Backed Securities [Member] \| Short-term Investments [Member]
Fair Value Measurements [Line Items]
Available for sale debt securities fair value	$ 54,400,000		$ 35,200,000

Fair Value Measurements - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 54,328	$ 36,336
Unrealized Gains	86	5
Unrealized Losses	(38)	(5)
Fair Value	54,376	36,336
Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	36,987	15,675
Unrealized Gains	85	5
Fair Value	37,072	15,680
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	15,041	18,361
Unrealized Gains	1
Unrealized Losses	(38)	(5)
Fair Value	15,004	18,356
Asset Back Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,300	2,300
Fair Value	$ 2,300	$ 2,300

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Short-term deposits	$ 2,343	$ 1,297
Prepaid clinical supplies	152	166
Interest receivable on investments	167	116
Reimbursable costs	324	416
Prepaid insurance	1,693	214
Other	407	347
Total prepaid expenses and other current assets	$ 5,086	$ 2,556

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued professional fees	$ 373	$ 403
Accrued compensation and related costs	1,223	2,800
Accrued clinical costs	5,664	6,726
Other	535	266
Total accrued expenses and other current liabilities	$ 7,795	$ 10,195

Stock-Based Compensation - Additional Information (Detail) - USD ($)		3 Months Ended		12 Months Ended
	Jan. 01, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Jan. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exercised, shares		51,034	0
Proceeds from stock option exercises		$ 338,000
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted to certain executives and employees		15,000
Shares, vesting period		4 years
Fair value of shares at grant date		142,000
Weighted average grant date fair value per share		$ 9.47
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance					1,085,619
2015 Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance		765,348
2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted to certain executives and employees		1,121,825
Options grant date fair value amount		$ 7,300,000
Weighted average grant date fair value of options		$ 6.52
Stock compensation expense		$ 50,000
Recognized compensation expense related to stock option not met		0
Sock option not met, options cancelled	194,338
2007 Plan [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted to certain executives and employees				583,000
2015 and 2007 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to stock option		$ 15,600,000
Weighted average period to recognize compensation expense		2 years 8 months 12 days

Stock-Based Compensation - Share Based Compensation Expense Related to Issuance of Stock Option Awards to Employees and Non Employees Related to Employee Stock Purchase Plan (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	$ 1,829	$ 1,592
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	532	534
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	$ 1,297	$ 1,058

Stock-Based Compensation - Compensation Expense by Type of Award (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	$ 1,829	$ 1,592
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	1,793	1,559
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense, total	$ 36	$ 33

Employee Stock Purchase Plan - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2020	Mar. 31, 2020	Mar. 31, 2019
Employee Benefit Plans [Line Items]
Compensation expense		$ 1,829	$ 1,592
Employee Stock Purchase Plan [Member]
Employee Benefit Plans [Line Items]
Common stock available for issuance	271,404
Number of shares issued under plan		12,601
Compensation expense		$ 36	$ 33
Employee Stock Purchase Plan [Member] \| Maximum [Member]
Employee Benefit Plans [Line Items]
Common stock available for issuance		1,115,797

Loan Payable - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended
	Oct. 01, 2020	Feb. 29, 2020	Mar. 31, 2020
Debt Instrument [Line Items]
Interest expense related to the loan agreement			$ 449,000
Hercules [Member] \| Loan Agreement [Member]
Debt Instrument [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.
Interest rate			9.85%
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
Interest expense related to the loan agreement			$ 400,000
Hercules [Member] \| Loan Agreement [Member] \| Scenario Forecast [Member]
Debt Instrument [Line Items]
Minimum cash covenant	$ 12,500,000
Default interest rate	5.00%
Hercules [Member] \| Loan Agreement [Member] \| Performance Milestone [Member]
Debt Instrument [Line Items]
Maturity date		Mar. 01, 2024
Hercules [Member] \| Loan Agreement [Member] \| Wall Street Journal Prime Rate [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		5.10%
Hercules [Member] \| Loan Agreement [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate		9.85%
Hercules [Member] \| Loan Agreement [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Percentage of repayment on aggregate principal amount of term loan advances		4.99%
Hercules [Member] \| Loan Agreement [Member] \| Term Loan [Member]
Debt Instrument [Line Items]
Term loan		$ 20,000,000
Hercules [Member] \| Loan Agreement [Member] \| Additional Term Loan [Member]
Debt Instrument [Line Items]
Term loan		10,000,000
Hercules [Member] \| Loan Agreement [Member] \| Tranche 2 [Member]
Debt Instrument [Line Items]
Facility charge paid		$ 50,000

Loan Payable - Summary of Maturities of Principal Obligations Under Long-term Debt (Detail) $ in Thousands	Mar. 31, 2020 USD ($)
Debt Disclosure [Abstract]
2021	$ 3,057
2022	9,809
2023	7,134
Total principal outstanding	20,000
Unamortized final fee	49
Unamortized debt issuance costs	(257)
Total	$ 19,792

Stockholders' Equity - Summary of Changes in Stockholders' Equity (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2020	Mar. 31, 2020	Mar. 31, 2019
Class of Stock [Line Items]
Beginning balance	$ 31,600	$ 31,600	$ 53,047
Proceeds from 'at-the-market' offering, net, value			830
Stock-based compensation expense		1,829	1,592
Proceeds from direct offering, net, value		24,201	10,922
Proceeds from pre-funded common stock warrant from direct offering, net, value		10,665	13,032
Issuance of common stock warrant with direct offering, value			$ 3,446
Repricing Series 1 and 2 warrants	3,900
Proceeds from exercise of stock options, value		$ 338
Proceeds from exercise of stock options, shares		51,034	0
Unrealized gains on short-term investments		$ 48	$ 33
Employee withholdings ESPP		64	26
Net loss		(15,236)	(14,302)
Ending balance		53,509	68,626
Series 1 and 2 [Member]
Class of Stock [Line Items]
Deemed dividend from repricing Series 1 and 2 warrants		3,906
Repricing Series 1 and 2 warrants		(3,906)
Common Stock [Member]
Class of Stock [Line Items]
Beginning balance	$ 3	$ 3	$ 2
Beginning balance, Shares	27,140,484	27,140,484	24,835,951
Stock purchase under ESPP, Shares		12,601	23,970
Proceeds from "at-the-market" offering, net, shares			140,819
Proceeds from direct offering, net, value			$ 1
Proceeds from direct offering,net, Shares		3,036,719	2,095,039
Proceeds from exercise of stock options, shares		51,034
Ending balance		$ 3	$ 3
Ending balance, Shares		30,240,838	27,095,779
Additional Paid-In Capital [Member]
Class of Stock [Line Items]
Beginning balance	$ 527,067	$ 527,067	$ 492,493
Proceeds from 'at-the-market' offering, net, value			830
Stock-based compensation expense		1,829	1,592
Proceeds from direct offering, net, value		24,201	10,921
Proceeds from pre-funded common stock warrant from direct offering, net, value		10,665	13,032
Issuance of common stock warrant with direct offering, value			3,446
Proceeds from exercise of stock options, value		338
Employee withholdings ESPP		64	26
Ending balance		564,164	522,340
Additional Paid-In Capital [Member] \| Series 1 and 2 [Member]
Class of Stock [Line Items]
Deemed dividend from repricing Series 1 and 2 warrants		3,906
Repricing Series 1 and 2 warrants		(3,906)
Accumulated Other Comprehensive Income / (Loss) [Member]
Class of Stock [Line Items]
Beginning balance			(25)
Unrealized gains on short-term investments		48	33
Ending balance		48	8
Accumulated Deficit [Member]
Class of Stock [Line Items]
Beginning balance	$ (495,470)	(495,470)	(439,423)
Net loss		(15,236)	(14,302)
Ending balance		$ (510,706)	$ (453,725)

Stockholders' Equity - Summary of Changes in Stockholders' Equity (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Equity [Abstract]
At-the-market, offering expenses		$ 34
Direct offering, common stock warrants		1,571
Direct offering, offering expenses	$ 93	78
Pre-funded common stock warrants		1,875
Pre-funded common stock warrants offering expenses	$ 41	$ 93

Stockholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Millions	1 Months Ended						3 Months Ended
	May 06, 2020 shares	Mar. 31, 2020 $ / shares shares	Jan. 31, 2020 USD ($) $ / shares shares	Aug. 31, 2019 USD ($)	Mar. 31, 2019 USD ($) Seriesofwarrant $ / shares shares	Apr. 30, 2017 USD ($)	Mar. 31, 2020 $ / shares shares	Mar. 31, 2019 USD ($) $ / shares shares
Class Of Stock [Line Items]
Common stock, new shares issued \| shares		2,095,039	3,036,719
Number of series of warrants \| Seriesofwarrant					2
Gross proceeds from offering \| $					$ 27.6
Offering costs \| $					$ 0.2
Weighted average expected term			4 months 24 days		1 year 4 months 24 days			1 year 4 months 24 days
Deemed dividend transferred to the warrant holders \| $			$ 3.9
Weighted Average Volatility Rate [Member]
Class Of Stock [Line Items]
Warrants and rights outstanding, measurement input			0.9674		0.891			0.891
Common Stock [Member]
Class Of Stock [Line Items]
Common stock, new shares issued \| shares					2,095,039
Pre-Funded Warrants [Member]
Class Of Stock [Line Items]
Warrants issued (in shares) \| shares			1,338,287		2,500,000			2,500,000
Warrant exercise price per share		$ 0.0001	$ 0.0001		$ 0.0001		$ 0.0001	$ 0.0001
Warrant term					20 years
Offering price			7.9999		$ 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%
Series Warrants [Member]
Class Of Stock [Line Items]
Warrants issued (in shares) \| shares					4,595,039			4,595,039
Warrant term							90 days
Offering price			8.00		$ 6.00
Weighted average price							$ 12.00
Total fair value of warrant \| $								$ 3.4
Series One Warrants [Member]
Class Of Stock [Line Items]
Warrant exercise price per share		12.00					12.00
Series Two Warrants [Member]
Class Of Stock [Line Items]
Warrant exercise price per share		$ 18.00					18.00
Maximum [Member] \| Series One Warrants [Member]
Class Of Stock [Line Items]
Warrant exercise price per share			12.00
Maximum [Member] \| Series Two Warrants [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]
Class Of Stock [Line Items]
Warrant exercise price per share			10.00
Minimum [Member] \| Series Two Warrants [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
Common stock, new shares issued \| shares							0	140,819
At The Market Equity Offering Sales Agreement [Member] \| Subsequent Event [Member]
Class Of Stock [Line Items]
Common stock, new shares issued \| shares	0
Cowen and Company LLC [Member] \| At The Market Equity Offering Sales Agreement [Member]
Class Of Stock [Line Items]
Proceeds from issuance of common stock in follow-on public stock offering, net \| $				$ 50.0		$ 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%

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Detail)	Mar. 31, 2020 shares
Pre-Funded Warrants [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	5,838,287
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	765,348
Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Common stock reserved for future issuance	1,115,797

Subsequent Event - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	May 31, 2020	Mar. 31, 2020	Jan. 31, 2020	Dec. 31, 2019
Subsequent Event [Line Items]
Common stock, new shares issued		2,095,039	3,036,719
Additional purchase of common stock		30,240,838		27,140,484
Underwritten Public Offering [Member] \| Scenario Forecast [Member]
Subsequent Event [Line Items]
Common stock, new shares issued	5,555,556
Offering price	$ 18.00
Proceeds from issuance of common stock, net	$ 93.7
Underwriters [Member] \| Scenario Forecast [Member]
Subsequent Event [Line Items]
Additional purchase of common stock	833,333