View Filing Data

Fair Value Measurements and Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 22,434	$ 45,210
Marketable securities	43,050	68,735
Total cash equivalents and marketable securities	65,484	113,945
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	18,289	40,231
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3,098
Marketable securities	14,996	3,994
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,047	4,979
Marketable securities	13,406	38,911
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	14,648	25,830
Quoted Prices in Active Markets, (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	18,289	40,231
Total cash equivalents and marketable securities	18,289	40,231
Quoted Prices in Active Markets, (Level 1) [Member] \| Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	18,289	40,231
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	4,145	4,979
Marketable securities	43,050	68,735
Total cash equivalents and marketable securities	47,195	73,714
Significant Other Observable Inputs (Level 2) [Member] \| U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3,098
Marketable securities	14,996	3,994
Significant Other Observable Inputs (Level 2) [Member] \| Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,047	4,979
Marketable securities	13,406	38,911
Significant Other Observable Inputs (Level 2) [Member] \| Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 14,648	$ 25,830

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 27,211	$ 49,331
Marketable securities	43,050	68,735
Tax incentive receivable	243	1,536
Prepaid expenses and other current assets	999	1,728
Total current assets	71,503	121,330
Property and equipment, net	821	375
Operating lease right-of-use assets	7,051
Restricted cash	1,339
Other assets	20	57
Total assets	80,734	121,762
Current liabilities:
Accounts payable	632	3,590
Accrued expenses	1,190	4,261
Accrued restructuring costs	2,709
Operating lease liabilities, current	386
Notes payable, current	7,273	5,455
Total current liabilities	12,190	13,306
Notes payable, long-term	8,464	15,185
Operating lease liabilities	6,456
Total liabilities	27,110	28,491
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred stock; $0.001 par value per share; 5,000,000 shares authorized as of December 31, 2019 and 2018; no shares issued and outstanding as of and December 31, 2019 and 2018
Common stock, $0.001 par value per share; 115,000,000 shares authorized as of December 31, 2019 and 2018; 37,446,498 and 37,287,221 shares issued and outstanding as of December 31, 2019 and 2018, respectively	37	37
Additional paid-in capital	449,903	444,212
Accumulated deficit	(396,351)	(350,945)
Accumulated other comprehensive income (loss)	35	(33)
Total stockholders' equity	53,624	93,271
Total liabilities and stockholders' equity	$ 80,734	$ 121,762

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance at Dec. 31, 2016	$ 121,727	$ 27	$ 359,329	$ (237,549)	$ (80)
Beginning balance, shares at Dec. 31, 2016		27,332,551
Issuance of common stock upon exercise of stock options and employee stock purchase plan	195		195
Issuance of common stock upon exercise of stock options and employee stock purchase plan, shares		136,992
Issuance of restricted stock units, shares		19,914
Stock-based compensation expense	8,301		8,301
Unrealized gain on marketable securities	22				22
Net loss	(52,028)			(52,028)
Ending balance at Dec. 31, 2017	78,217	$ 27	367,825	(289,577)	(58)
Ending balance, shares at Dec. 31, 2017		27,489,457
Issuance of common stock, net of issuance costs	64,410	$ 9	64,401
Issuance of common stock, net of issuance costs, shares		9,200,000
Issuance of common stock upon exercise of stock options and employee stock purchase plan	2,360	$ 1	2,359
Issuance of common stock upon exercise of stock options and employee stock purchase plan, shares		578,842
Issuance of restricted stock units, shares		18,922
Stock-based compensation expense	9,627		9,627
Unrealized gain on marketable securities	25				25
Net loss	(61,368)			(61,368)
Ending balance at Dec. 31, 2018	93,271	$ 37	444,212	(350,945)	(33)
Ending balance, shares at Dec. 31, 2018		37,287,221
Issuance of common stock upon exercise of stock options and employee stock purchase plan	194		194
Issuance of common stock upon exercise of stock options and employee stock purchase plan, shares		143,360
Issuance of restricted stock units, shares		15,917
Stock-based compensation expense	5,497		5,497
Unrealized gain on marketable securities	68				68
Net loss	(45,406)			(45,406)
Ending balance at Dec. 31, 2019	$ 53,624	$ 37	$ 449,903	$ (396,351)	$ 35
Ending balance, shares at Dec. 31, 2019		37,446,498

Commitments and Contingencies - Additional Information (Detail)					7 Months Ended	12 Months Ended
	Feb. 12, 2019 USD ($) ft²	Jan. 01, 2017 ft²	Oct. 01, 2015	Apr. 15, 2015 Option	Jul. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Other Commitments [Line Items]
Total lease payments over the initial term						$ 11,103,000
Sublease rental income						112,000
Impairment loss on operating lease right-of-use asset						100,000
Lease expense						1,044,000	$ 400,000	$ 300,000
Milestone payments due						0	$ 0	$ 0
Subsequent Licensed Product [Member]
Other Commitments [Line Items]
Licensing fees per product maximum						1,300,000
Maximum [Member] \| Pre Commercialization Milestones [Member]
Other Commitments [Line Items]
Milestone payments						12,300,000
Maximum [Member] \| Product Commercialization Milestones [Member]
Other Commitments [Line Items]
Milestone payments						12,500,000
Research and Development [Member]
Other Commitments [Line Items]
Lease expense						600,000
General and Administrative [Member]
Other Commitments [Line Items]
Lease expense						$ 400,000
Additional Boston Office Space [Member]
Other Commitments [Line Items]
Lease extension period				3 years
Operating lease, existence of option to extend				true
Lease expiration date				Jul. 31, 2020
Number of options to extend lease \| Option				1
Boston Office Space [Member] \| Unrelated Third Party [Member]
Other Commitments [Line Items]
Subleased area \| ft²		2,976
Sublease expiration date		Jul. 31, 2020
Boston Office Space [Member] \| Unrelated Third Party [Member] \| Scenario Forecast [Member]
Other Commitments [Line Items]
Sublease rental income					$ 100,000
San Diego Office Space [Member]
Other Commitments [Line Items]
Lease expiration date			Dec. 31, 2024
Center Plaza, Boston [Member] \| Massachusetts [Member] \| Shigo Center Plaza Owners LLC [Member]
Other Commitments [Line Items]
Area of office space \| ft²	17,705
Operating lease term	124 months
Lease extension period	60 months
Letter of credit	$ 1,300,000
Operating lease, existence of option to extend	true
Total lease payments over the initial term	$ 10,700,000
Lease commencement date	Jun. 21, 2019

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities as of the date of the consolidated financial statements, and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.

Cash Equivalents

The Company considers all short-term, highly liquid investments with original maturities of ninety days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market funds, U.S. government securities, corporate bonds, and commercial paper, are stated at fair value.

Concentration of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company has all cash, cash equivalents and marketable securities balances at accredited financial institutions in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs, if and when development programs are active. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.

Marketable Securities

Marketable securities consist of investments with original maturities greater than ninety days. The Company has classified its investments with maturities beyond one year as short term, based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. The Company classifies its marketable securities as available-for-sale. Accordingly, these investments are recorded at fair value, which is based on quoted market prices. Unrealized gains and losses are reported as a component of accumulated other comprehensive loss in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other income (expense), net, based on the specific identification method. When determining whether a decline in value is other than temporary, the Company considers various factors, including whether the Company has the intent to sell the security, and whether it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis. Fair value is determined based on quoted market prices.

Deferred Offering Costs

The Company capitalizes certain legal, accounting and other third-party fees that are directly associated with in-process equity financings as other assets until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity as a reduction of additional paid-in capital generated as a result of the offering or as a reduction to the carrying value of preferred stock issued.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over a three or five-year estimated useful life for equipment, furniture and fixtures and office equipment. Leasehold improvements are amortized over the shorter of the asset life or the term of the lease agreement. Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations.

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment, net¸and the net operating lease asset. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. Any impairment loss, if indicated, is measured as the amount by which the carrying amount of the asset exceeds the estimated fair value of the asset. To date, the Company has recorded $0.1 million impairment losses on long-lived assets associated with the restructuring announced in September 2019.

Research and Development Costs

Research and development costs are expensed as incurred. Included in research and development expenses are wages, stock-based compensation and benefits of employees, third-party license fees and milestones and other operational costs related to the Company’s research and development activities, including facility-related expenses and external costs of outside vendors engaged to conduct nonclinical studies, manufacturing activities, and clinical trials. The Company records research and development expenses net of any research and development tax incentives the Company is entitled to receive from government authorities.

Research Contract Costs and Accruals

The Company has, from time to time, entered into various research and development contracts with research institutions and other companies both inside and outside of the United States. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Patent Costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are recorded as general and administrative expenses as incurred, as recoverability of such expenditures is uncertain.

Accounting for Stock-Based Compensation

The Company measures all stock-based awards granted to employees, non-employee consultants and directors based on the fair value on the date of grant using the Black-Scholes option-pricing model. Compensation expense of those awards is recognized over the requisite service period, which is generally the vesting period of the respective award. Typically, the Company issues awards with only service-based and market-based vesting conditions and records the expense for these awards using the straight-line method. The Company accounts for forfeitures as they occur.

The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.

Income Taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Segment Data

The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company is a biopharmaceutical company that has leveraged its proprietary knowledge of the MetAP2 pathway to pioneer the study of MetAP2 inhibitors in both common and rare metabolic disorders. No revenue has been generated since inception, and all tangible assets are held in the United States.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2019, 2018 and 2017, the Company’s only element of other comprehensive income was unrealized gain on marketable securities.

Net Loss Per Share

Basic net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of common shares, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common shares, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is antidilutive.

Recently Issued and Adopted Accounting Pronouncements

In February 2016, the Financial Accounting Standards Board (the “FASB”) issued ASU No. 2016-02, Leases and in July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. The new leasing standards generally require lessees to recognize operating and financing lease liabilities and corresponding right-of-use assets on the consolidated balance sheet and to provide enhanced disclosures surrounding the amount, timing and uncertainty of cash flows arising from leasing arrangements.

We adopted the new leasing standards using the modified retrospective transition approach, as of January 1, 2019, with no restatement of prior periods or cumulative adjustment to retained earnings. Upon adoption, we elected the package of transition practical expedients, which allowed us to carry forward prior conclusions related to whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases and initial direct costs for existing leases. In addition, the Company elected the hindsight practical expedient to determine the lease term for existing leases. The Company elected not to record leases with an initial term of 12 months or less on the balance sheet and recognize the associated lease payments in the consolidated statements of operations on a straight-line basis over the lease term. Upon adoption of the new leasing standards we recognized an operating lease asset of approximately $1.0 million and a corresponding operating lease liability of approximately $1.0 million, which are included in our consolidated balance sheet. The adoption of the new leasing standards did not have an impact on our consolidated statements of income or cash flows.

We determine if an arrangement is a lease at contract inception. Operating lease assets represent our right to use an underlying asset for the lease term and operating lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease assets and liabilities are recognized at the commencement date of the lease based upon the present value of lease payments over the lease term. When determining the lease term, we include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. We use the implicit rate when readily determinable and use our incremental borrowing rate when the implicit rate is not readily determinable based upon the information available at the commencement date in determining the present value of the lease payments. Our incremental borrowing rate is determined using a secured borrowing rate for the same currency and term as the associated lease.

The lease payments used to determine our operating lease assets may include lease incentives, stated rent increases and escalation clauses linked to rates of inflation when determinable and are recognized in our operating lease assets in our consolidated balance sheets.

Our operating leases are reflected in operating lease right-of-use assets, short-term operating lease liabilities and in long-term operating lease liabilities in our consolidated balance sheets. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term.

For additional information on the adoption of the new leasing standards, please read Note 10, Commitments and Contingencies, to these consolidated financial statements.

In June 2018, the FASB issued ASU No. 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. This ASU is intended to simplify aspects of share-based compensation issued to non-employees by making the guidance consistent accounting for employee share-based compensation. This standard was effective for the Company in 2019. The adoption of this guidance had an immaterial impact on the Company’s consolidated financial statements as of and for the year ended December 31, 2019.

In August 2018 the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. This standard modifies certain disclosure requirements on fair value measurements. This standard became effective for the Company on January 1, 2020. The adoption of this standard will not have a material impact on the Company’s disclosures.

Stock-Based Awards - Additional Information (Detail) - USD ($)		1 Months Ended		12 Months Ended
	Jan. 01, 2019	Aug. 31, 2018	Oct. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Options with Time-Based Vesting Conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, stock options granted				2,276,197
Aggregate intrinsic value of stock options exercised					$ 1,600,000	$ 300,000
Proceeds from exercise of common stock options				$ 100,000	$ 2,200,000	$ 100,000
Weighted average grant-date fair value of stock options granted				$ 3.14	$ 6.08	$ 2.91
Stock based compensation, stock options forfeited				3,252,814
Aggregate intrinsic value of Price Target Options					$ 3,143,000
Average remaining contractual life, outstanding				6 years 8 months 12 days	7 years 7 months 6 days
Unrecognized stock-based compensation cost				$ 6,100,000
Stock-based compensation recognized weighted average period				2 years 7 months 6 days
Options with Time-Based Vesting Conditions [Member] \| Non Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of outstanding unvested shares held by nonemployees				25,834	45,209
Options with Time-Based Vesting Conditions [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of stock options exercised				$ 100,000
Options with Market-Based Vesting Conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, stock options granted			687,500
Vesting period of stock option				3 years
Stock option vesting description			Company granted 687,500 common stock options that vest on the third anniversary of the grant date upon achievement by the Company of minimum common stock prices for 20 consecutive days during the Earning Period, the (“Price Target Options”).
Total fair value of Price Target Options				$ 3,100,000
Weighted average fair value of Price Target Options				$ 4.56
Unrecognized stock-based compensation cost				$ 700,000
Stock-based compensation recognized weighted average period				9 months 18 days
Options with Market-Based Vesting Conditions [Member] \| CEO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, stock options granted			550,000			550,000
Term of stock option			10 years
Aggregate intrinsic value of Price Target Options				$ 0
Average remaining contractual life, outstanding				7 years 9 months 7 days
Options with Market-Based Vesting Conditions [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares that will vest upon achievement of the target, as a percentage				50.00%
Options with Market-Based Vesting Conditions [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares that will vest upon achievement of the target, as a percentage				200.00%
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of stock option				1 year
Number of restricted stock units granted				355,187	17,856	22,128
Weighted average grant-date fair value of restricted stock units granted				$ 4.38	$ 5.18	$ 4.18
Aggregate intrinsic value of restricted stock units vested during the period					$ 200,000	$ 100,000
2014 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance				2,168,221
Percentage of outstanding shares of common stock				4.00%
Shares available for grant				5,278,653
Shares added to plan	1,491,488
2014 Stock Option and Incentive Plan [Member] \| Options with Time-Based Vesting Conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, stock options granted				1,901,197	1,823,386	1,214,874
2014 Stock Option and Incentive Plan [Member] \| Options with Time-Based Vesting Conditions [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of stock option				3 years
2014 Stock Option and Incentive Plan [Member] \| Options with Time-Based Vesting Conditions [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of stock option				4 years
2014 Stock Option and Incentive Plan [Member] \| Options with Market-Based Vesting Conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, stock options granted			137,500
Term of stock option			10 years
Stock based compensation, stock options forfeited		137,500
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance				265,000
Shares available for grant				69,522	129,835
Commencement date of first offering period				Jan. 01, 2019	Jan. 01, 2018
End date of first offering period				Jun. 30, 2019	Jun. 30, 2018
Commencement date of second offering period				Jul. 01, 2019	Jul. 01, 2018
End date of second offering period				Dec. 31, 2019	Dec. 31, 2018
Stock-based awards, shares				60,313	46,181
2014 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount from market price of the company's common stock offering				85.00%
Grants Outside of 2014 Plan [Member] \| Options with Time-Based Vesting Conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, stock options granted				375,000	225,000	550,000
Term of stock option				10 years
Stock option vesting description				The options vest as to 25% of the shares on the first anniversary of the grant date and the remainder in equal monthly installments thereafter over a 3-year period.
Grants Outside of 2014 Plan [Member] \| Options with Time-Based Vesting Conditions [Member] \| First Anniversary of Grant Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting percentage				25.00%

Fair Value Measurements and Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Summary of Cash Equivalents and Marketable Securities

The following tables summarize the Company’s cash equivalents and marketable securities as of December 31, 2019 and 2018:

	December 31, 2019
			Quoted		Significant
			Prices in		Other			Significant
			Active		Observable			Unobservable
			Markets		Inputs			Inputs
	Total		(Level 1)		(Level 2)			(Level 3)
	(in thousands)
Cash equivalents:
Money market funds	$	18,289	$	18,289	$	—	$		—
U.S. Government securities		3,098		—		3,098			—
Commercial paper		1,047		—		1,047			—
Total cash equivalents		22,434		18,289		4,145			—
Marketable securities:
U.S. Government securities		14,996		—		14,996			—
Corporate bonds		14,648		—		14,648			—
Commercial paper		13,406		—		13,406			—
Total marketable securities		43,050		—		43,050			—
Total cash equivalents and marketable securities	$	65,484	$	18,289	$	47,195		$	—

	December 31, 2018
			Quoted		Significant
			Prices in		Other		Significant
			Active		Observable		Unobservable
			Markets		Inputs		Inputs
	Total		(Level 1)		(Level 2)		(Level 3)
	(in thousands)
Cash equivalents:
Money market funds	$	40,231	$	40,231	$	—	$	—
Commercial paper		4,979		—		4,979		—
Total cash equivalents		45,210		40,231		4,979		—
Marketable securities:
Commercial paper		38,911		—		38,911		—
Corporate bonds		25,830		—		25,830		—
U.S. Government securities		3,994		—		3,994		—
Total marketable securities		68,735		—		68,735		—
Total cash equivalents and marketable securities	$	113,945	$	40,231	$	73,714	$	—

Summary of Marketable Securities

The following tables summarize the Company’s marketable securities as of December 31, 2019 and 2018:

	December 31, 2019
			Gross		Gross
	Amortized		Unrealized		Unrealized
	Cost		Gains		Losses		Fair Value
	(in thousands)
Assets:
U.S. Government securities (due within 1 year)	$	14,981	$	15	$	—	$	14,996
Corporate bonds (due within 1 year)		14,628		20		—		14,648
Commercial paper (due within 1 year)		13,406		—		—		13,406
	$	43,015	$	35	$	—	$	43,050

	December 31, 2018
			Gross		Gross
	Amortized		Unrealized		Unrealized
	Cost		Gains		Losses			Fair Value
	(in thousands)
Assets:
Commercial paper (due within 1 year)	$	38,921	$	—	$	(10	)	$	38,911
Corporate bonds (due within 1 year)		25,851		3		(24	)		25,830
U.S. Government securities (due within 1 year)		3,995		—		(1	)		3,994
	$	68,767	$	3	$	(35	)	$	68,735

Stock-Based Awards - Summary of Stock Option Activity (Detail) - Options with Time-Based Vesting Conditions [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issuable under options, beginning balance	5,024,371
Shares issuable under options, granted	2,276,197
Shares issuable under options, exercised	(83,047)
Shares issuable under options, forfeited	(3,252,814)
Shares issuable under options, ending balance	3,964,707	5,024,371
Shares issuable under options, options exercisable	1,700,815
Weighted average exercise price, beginning balance	$ 8.85
Weighted average exercise price, granted	4.00
Weighted average exercise price, exercised	0.81
Weighted average exercise price, forfeited	8.81
Weighted average exercise price, ending balance	6.26	$ 8.85
Weighted average exercise price, options exercisable	$ 8.49
Average remaining contractual life, outstanding	6 years 8 months 12 days	7 years 7 months 6 days
Average remaining contractual life, options exercisable	6 years 9 months 18 days
Aggregate intrinsic value, outstanding		$ 3,143

Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Data (Unaudited)

15. Quarterly Financial Data (Unaudited)

The following information has been derived from unaudited consolidated financial statements that, in the opinion of management, include all recurring adjustments necessary for a fair statement of such information.

	Three Months Ended
	March 31,			June 30,			September 30,			December 31,
	2019			2019			2019			2019
	(in thousands, except per share data)
Revenue	$	—		$	—		$	—		$	—
Operating expenses		13,277			12,190			12,906			7,281
Net loss		(13,112	)		(12,129	)		(12,914	)		(7,251	)
Net loss per share, basic and diluted	$	(0.35	)	$	(0.32	)	$	(0.35	)	$	(0.19	)
Weighted average common shares outstanding, basic and diluted		37,313,947			37,326,853			37,369,829			37,377,223


	Three Months Ended
	March 31,			June 30,			September 30,			December 31,
	2018			2018			2018			2018
	(in thousands, except per share data)
Revenue	$	—		$	—		$	—		$	—
Operating expenses		15,702			15,560			15,169			14,691
Net loss		(15,956	)		(15,775	)		(15,067	)		(14,570	)
Net loss per share, basic and diluted	$	(0.58	)	$	(0.57	)	$	(0.41	)	$	(0.39	)
Weighted average common shares outstanding, basic and diluted		27,541,594			27,565,064			36,619,575			37,036,065

Stock-Based Awards

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Awards

8. Stock-Based Awards

Stock Option Plan

The Company’s 2014 Stock Option and Incentive Plan (the “2014 Plan”) provides for the grant of stock options, stock appreciation rights, restricted stock awards, restricted stock units, unrestricted stock awards, performance-share awards, cash-based awards and dividend equivalent rights to employees, members of the board of directors and consultants of the Company. The number of shares initially reserved for issuance under the 2014 Plan was 2,168,221 shares of common stock. The number of shares reserved for issuance may be increased by the number of shares under the previously authorized 2006 Stock Option Plan that are not needed to fulfill the Company’s obligations for awards issued under the 2006 Stock Option Plan as a result of forfeiture, expiration, cancellation, termination or net issuances of awards thereunder. The number of shares of common stock that may be issued under the 2014 Plan is also subject to increase on the first day of each fiscal year by the lesser of (i) 4% of the Company’s outstanding shares of common stock as of that date, or (ii) an amount determined by the board of directors. As of December 31, 2019, 5,278,653 shares are available for grant under the 2014 Plan, including 1,491,488 shares automatically added to the 2014 Plan on January 1, 2019, and 69,522 shares are available for issuance to participating employees under the ESPP.

Stock Option Grants

Option Grants with time-based vesting conditions

During the years ended December 31, 2019, 2018 and 2017, the Company granted 1,901,197, 1,823,386 and 1,214,874 stock options, respectively, under the 2014 Plan. The vesting of these awards is time-based and the restrictions typically lapse over periods of three to four years. Stock options were granted with exercise prices equal to the fair value of the Company’s common stock on the date of grant. The Company bases fair value of common stock on the quoted market price of the Company’s common stock. During the years ended December 31, 2019, 2018 and 2017 the Company granted 375,000, 225,000, and 550,000 options, respectively, with time-based vesting as inducement grants outside of the 2014 Plan in accordance with NASDAQ Listing Rule 5635(c)(4). These stock options have a ten-year term and an exercise price equal to the closing price of the Company’s common stock on the grant date. The options vest as to 25% of the shares on the first anniversary of the grant date and the remainder in equal monthly installments thereafter over a 3-year period.

The fair value of each service-based stock option grant to employees and directors is estimated on the date of grant using the Black-Scholes option-pricing model. The Company estimates its expected volatility using a weighted average of the historical volatility of publicly-traded peer companies and its own common stock since its IPO in June 2014, and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price for the duration of the expected term. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors are as follows, presented on a weighted average basis:

	2019			2018			2017
Risk-free interest rate		2.49	%		2.77	%		2.10	%
Expected term (in years)		6.17			6.17			6.17
Expected volatility		96	%		100	%		93	%
Expected dividend yield		0	%		0	%		0	%

The following table summarizes the Company’s stock option activity described above, since December 31, 2018:

	Shares			Weighted		Average
	Issuable			Average		Remaining	Aggregate
	Under			Exercise		Contractual	Intrinsic
	Options			Price		Term	Value
						(in years)	(in thousands)
Outstanding as of December 31, 2018		5,024,371		$	8.85	7.6	$	3,143
Granted		2,276,197		$	4.00
Exercised		(83,047	)	$	0.81
Forfeited		(3,252,814	)	$	8.81
Outstanding as of December 31, 2019		3,964,707		$	6.26	6.7	$	—
Options exercisable as of December 31, 2019		1,700,815		$	8.49	6.8	$	—

The aggregate intrinsic value was calculated based on the positive differences between the market value of the Company’s common stock and the exercise prices of the options. The aggregate intrinsic value of service-based stock options exercised was less than $0.1 million, $1.6 million and $0.3 million during the years ended December 31, 2019, 2018 and 2017, respectively.

The Company received cash proceeds from the exercise of stock options of $0.1 million, $2.2 million, and $0.1 million during the years ended December 31, 2019, 2018 and 2017, respectively.

The weighted average grant-date fair value of service-based stock options granted to employees and directors during the years ended December 31, 2019, 2018 and 2017 was $3.14, $6.08 and $2.91, per share, respectively.

As of December 31, 2019 and 2018, there were outstanding unvested service-based stock options held by nonemployees for the purchase of 25,834 and 45,209 shares of common stock, respectively.

Option Grants with market-based vesting conditions

In October 2017, the Company granted 687,500 common stock options that vest on the third anniversary of the grant date upon achievement by the Company of minimum common stock prices for 20 consecutive days during the Earning Period, the (“Price Target Options”). The Earning Period is defined as the period between the first anniversary of the grant date and the third anniversary of the grant date. Of the 687,500 Price Target Options granted in 2017, 137,500 were granted under the 2014 Stock Plan and 550,000 were granted to the newly-hired Chief Executive Officer as an inducement grant outside of the 2014 Plan in accordance with NASDAQ Listing Rule 5635(c)(4). These stock options have a ten-year term and an exercise price equal to the closing price of the Company’s common stock on the grant date. In August 2018, the 137,500 shares granted under the 2014 Stock Plan were forfeited.

The number of Price Target Options that will vest upon achievement of the target will vary based on the level of achievement from a maximum of 200% of the target shares to a threshold of 50% of the target shares, with no vesting, absent certain circumstances, if the threshold requirement is not achieved or the employee is no longer with the Company at the end of the three-year period. The Price Target Options are valued using Monte Carlo simulation models. The number of options expected to vest, based on achievement of the specified market condition, is factored into the grant date Monte Carlo valuations for the Price Target Options. Compensation expense is recognized ratably over the attribution period.

The assumptions that the Company used to determine the fair value of the Price Target Options granted to employees were as follows, presented on a weighted average basis:

	2017
Risk-free interest rate		2.24	%
Expected term (in years)		6.30
Expected volatility		95	%
Expected dividend yield		0	%

The Price Target Options had a grant date total fair value of $3.1 million and a weighted average fair value of $4.56 per share. As of December 31, 2019, the 550,000 Price Target Options had an aggregate intrinsic value of $0 and a remaining contractual term of 7.77 years.

Restricted Stock Units

Restricted stock units awarded to employees generally vest one-half on the anniversary of the date of grant and the remaining one-half on the 18-month anniversary of the date of grant, provided the employee remains continuously employed with us, except as otherwise provided in the plan. Shares of our common stock will be delivered to the employee upon vesting, subject to payment of applicable withholding taxes. Restricted stock units are awarded to directors in lieu of cash fees for service on our Board of Directors and vest quarterly over a one year period, provided in each case that the director continues to serve on our Board of Directors through the vesting date. Shares of our common stock will be delivered to the director upon vesting and are not subject to any withholding taxes.

				Weighted
				Average
				Grant Date
	Shares			Fair Value

Unvested at December 31, 2018		—		$	—
Granted		355,187		$	4.62
Vested		(15,267	)	$	4.38
Forfeited		(290,784	)	$	4.63
Unvested at December 31, 2019		49,136		$	4.63

During the years ended December 31, 2018 and 2017, the Company granted 17,856 and 22,128 restricted stock units, respectively, all of which vested during 2018 and 2017, respectively, at a weighted average grant-date fair value of $5.18 and $4.18, respectively. The aggregate intrinsic value of restricted stock units that vested during the years ended December 31, 2018 and 2017 was $0.2 million and $0.1 million, respectively, calculated as the fair value of the Company’s common stock on the date it vests.

2014 Employee Stock Purchase Plan

The Company has a 2014 Employee Stock Purchase Plan (the “ESPP”) under which a total of 265,000 shares of common stock were reserved for issuance. During both 2019 and 2018 there were two offering periods, January 1 through June 30 and July 1 through December 31. The per share purchase price for offerings is equal to the lesser of 85% of the closing market price of the Company’s common stock on the first day or last day of the offering period. The Company issued 60,313 and 46,181 shares during the years ended December 31, 2019 and 2018, respectively. As of December 31, 2019 and 2018, there are 69,522 and 129,835 shares, respectively, of common stock available for issuance to participating employees under the ESPP.

Stock-based Compensation

The Company recorded stock-based compensation expense related to stock options and restricted common stock in the following expense categories within its consolidated statements of operations:

	Year Ended December 31,
	2019		2018		2017
	(in thousands)
Research and development	$	1,322	$	5,476	$	4,138
General and administrative		4,175		4,151		4,163
	$	5,497	$	9,627	$	8,301

As of December 31, 2019, the Company had unrecognized stock-based compensation expense related to its unvested service-based stock option awards of $6.1 million, which is expected to be recognized over the remaining weighted average vesting period of 2.6 years.

As of December 31, 2019, the Company had unrecognized stock-based compensation expense related to its unvested market-based stock option awards of $0.7 million, which is expected to be recognized over the remaining weighted average vesting period of 0.8 years.

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Mar. 01, 2020	Jun. 28, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	ZAFGEN, INC.
Entity Central Index Key	0001374690
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		37,469,596
Entity Public Float			$ 40.1
Entity File Number	001-36510
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-3857670
Entity Address, Address Line One	3 Center Plaza
Entity Address, Address Line Two	Suite 610
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02108
City Area Code	617
Local Phone Number	622-4003
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock
Trading Symbol	ZFGN
Security Exchange Name	NASDAQ
Documents Incorporated by Reference	The registrant intends to file a definitive proxy statement pursuant to Regulation 14A within 120 days of the end of the fiscal year ended December 31, 2019. Portions of such definitive proxy statement are incorporated by reference into Part III of this Annual Report on Form 10-K.

Restructuring (Tables)

12 Months Ended

Dec. 31, 2019

Restructuring And Related Activities [Abstract]

Summary of Accrued Restructuring Costs

The following table shows the total amount expected to be incurred and the liability related to the 2019 restructuring as of December 31, 2019:

	Year Ended December 31, 2019
	(in thousands)
	One-Time
	Employee			Contract
	Termination			Termination			Total
	Benefits			Costs			Expenses

Accrued restructuring costs beginning balance	$	—		$	—		$	—
Restructuring charges incurred during the period		4,062			1,411			5,473
Amounts paid during the period		(1,356	)		(1,408	)		(2,764	)
Accrued restructuring costs as of December 31, 2019	$	2,706		$	3		$	2,709

Summary of Restructuring Charges by Category

The following table summarizes the restructuring charges by category for the period ending December 31, 2019:

	Year Ended December 31, 2019
	(in thousands)
	Cash		Non-Cash		Total
Research and development	$	5,038	$	80	$	5,118
General and administrative		435		—		435
	$	5,473	$	80	$	5,553

Restructuring

12 Months Ended

Dec. 31, 2019

Restructuring And Related Activities [Abstract]

Restructuring

14. Restructuring

In September 2019, the Company’s Board of Directors approved a restructuring plan to reduce operating costs and better align the Company’s workforce with the needs of its business following the Company’s September 5, 2019 announcement regarding the low probability of resolving the clinical hold of ZGN-1061 in the near-term and that the Company will be seeking strategic alternatives.

Under the restructuring plan and a previously announced July 2019 restructuring, the Company reduced its workforce by 20 employees and closed its office in San Diego, California. Affected employees are eligible to receive severance payments and outplacement services in connection with the reduction. In the year ended December 31, 2019, the Company recorded aggregate restructuring charges of approximately $5.6 million related to contract termination, closing of its office in San Diego, severance payments and other employee-related costs. The Company does not expect to incur any additional significant costs associated with these restructurings. During the year ended December 31, 2019, $2.8 million of the estimated restructuring charges were paid. The Company expects the remaining accrued restructuring costs of $2.7 million will be paid in the next 12 months.

The following table shows the total amount expected to be incurred and the liability related to the 2019 restructuring as of December 31, 2019:

	Year Ended December 31, 2019
	(in thousands)
	One-Time
	Employee			Contract
	Termination			Termination			Total
	Benefits			Costs			Expenses

Accrued restructuring costs beginning balance	$	—		$	—		$	—
Restructuring charges incurred during the period		4,062			1,411			5,473
Amounts paid during the period		(1,356	)		(1,408	)		(2,764	)
Accrued restructuring costs as of December 31, 2019	$	2,706		$	3		$	2,709

The following table summarizes the restructuring charges by category for the period ending December 31, 2019:

	Year Ended December 31, 2019
	(in thousands)
	Cash		Non-Cash		Total
Research and development	$	5,038	$	80	$	5,118
General and administrative		435		—		435
	$	5,473	$	80	$	5,553

Nature of the Business and Basis of Presentation

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Nature of the Business and Basis of Presentation

1. Nature of the Business and Basis of Presentation

Zafgen, Inc., or the Company, was incorporated on November 22, 2005 under the laws of the State of Delaware. The Company is a biopharmaceutical company that has leveraged its proprietary knowledge of the methionine aminopeptidase 2 (“MetAP2”) pathway to pioneer the study of MetAP2 inhibitors in both common and rare metabolic disorders.

The Company’s prior lead product candidate, ZGN-1061, is a MetAP2 inhibitor that was in Phase 2 clinical development for the treatment of type 2 diabetes and other related metabolic disorders. In November 2018, the Company received a letter from the U.S. Food and Drug Administration (“FDA”) placing a full clinical hold on the investigational new drug application (“IND”) for the first U.S. clinical trial of ZGN-1061. The FDA cited the possibility of cardiovascular (“CV”) safety risk based on the Company’s prior compound. In July 2019, the Company reached agreement with the FDA on an in vivo animal study design and protocol to establish relevant safety margins for ZGN-1061. The study was designed to translate the data from the Company’s newly developed in vitro assays of human endothelial cells and assessment of tissue factor expression with endothelial cells, along with other supportive assays, as it worked toward resolving the full clinical hold. Based on the preliminary results from the in vivo study, on September 5, 2019, the Company announced that it believes there is a low probability of resolving the clinical hold in the near-term. Subsequently, all further development activities of MetAP2 inhibitors were halted and the Company withdrew the IND for ZGN-1061 in September 2019. Therefore, the Company determined that it is in the best interest of shareholders to evaluate strategic alternatives and implemented a restructuring plan to reduce operating costs and better align the Company’s workforce with its needs, which in combination with the July restructuring actions and other attrition in 2019, resulted in a 70% reduction in workforce and closure of its San Diego facility (See Note 14).

Following an extensive process of evaluating strategic alternatives for the Company and identifying and reviewing potential candidates for a strategic acquisition or other transaction, on December 17, 2019, the Company entered into an Agreement and Plan of Merger, or the Merger Agreement, with Chondrial Therapeutics, Inc. (“Chondrial”), pursuant to which a wholly owned subsidiary of the Company will merge with and into Chondrial, with Chondrial continuing as the surviving corporation and a wholly owned subsidiary of the Company and the combined publicly traded, clinical-stage biopharmaceutical company will operate under a new name, Larimar Therapeutics, Inc. Under the exchange ratio formula in the Merger Agreement, as of immediately after the merger, the former Chondrial securityholders are expected to own approximately 60% of the outstanding shares of Zafgen common stock on a fully-diluted basis and the Company’s stockholders as of immediately prior to the merger are expected to own approximately 40% of the outstanding shares of our common stock on a fully-diluted basis. Under certain circumstances further described in the Merger Agreement, the ownership percentages may be adjusted upward or downward based on the level of our net cash at the closing of the merger and certain other adjustments. The Company expects to devote significant time and resources to completion of this proposed transaction, which the Company refers to as the Merger. However, there can be no assurance that such activities will result in the completion of the Merger. Further, the completion of the Merger ultimately may not deliver the anticipated benefits or enhance shareholder value.

The Merger Agreement provides each of the Company and Chondrial with specified termination rights, and further provides that, upon termination of the Merger Agreement under specified circumstances, either party may be required to pay the other party a termination fee of $3,375,000. In addition, in connection with certain terminations of the Merger Agreement, either party may be required to pay the other party’s third party expenses up to $350,000. In connection with the merger, the Company will seek to amend our certificate of incorporation to: (i) effect a reverse split of our common stock at a ratio to be determined by us and Chondrial, which is intended to ensure that the listing requirements of the Nasdaq Global Market are satisfied and (ii) change the name of Zafgen to “Larimar Therapeutics, Inc.”

The Company’s and Chondrial’s obligations to consummate the merger are subject to the satisfaction or waiver of customary closing conditions, including, among others, obtaining the requisite approvals of our stockholders and satisfaction of minimum net cash thresholds of $30,000,000 by the Company and not less than zero by Chondrial. The sole stockholder of Chondrial has approved the Merger Agreement. In connection with the execution of the Merger Agreement, the Company entered into stockholder support agreements with the Company’s current directors and certain officers and the Company’s largest stockholder, which collectively beneficially own or control an aggregate of approximately 9.7% of the Company’s outstanding shares of common stock. Each of the stockholders party to such stockholder support agreements has agreed to vote or cause to be voted, all of the shares of the Company’s common stock beneficially owned by such stockholder in favor of the stockholder proposals submitted at our stockholders meeting to be held in connection with the merger.

The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Future product candidates, if any, will require significant additional research and development efforts, including extensive nonclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure, and extensive compliance-reporting capabilities.

As a result of our potential strategic alternative, there can be no assurance that the Company’s future product candidates’ research and development, if any, will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any product candidates developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants.

The Company has incurred losses and negative cash flows from operations since its inception. As of December 31, 2019, the Company had an accumulated deficit of $396.4 million. From its inception through December 31, 2019, the Company received net proceeds of $397.9 million from the sales of redeemable convertible preferred stock, the issuance of convertible promissory notes, the proceeds from its initial public offering (“IPO”) in June 2014 and its follow-on offerings in January 2015 and July 2018. On July 2, 2018, the Company completed a public offering of its common stock, which resulted in the sale of 9,200,000 shares at a price of $7.50 per share, resulting in net proceeds of approximately $64.6 million after deducting underwriting discounts and commissions, as well as offering costs. As disclosed in Note 6 to the consolidated financial statements, the Company has a term loan with an aggregate principal balance of $14.5 million as of December 31, 2019. The loan agreement with Silicon Valley Bank (the “Term Loan”) requires that the Company maintain certain minimum liquidity at all times, which as of December 31, 2019, was approximately $15.3 million. If the minimum liquidity covenant is not met, the Company may be required to repay the loan prior to scheduled maturity dates. The Term Loan also includes events of default, the occurrence and continuation of any of which provides the lenders the right to exercise remedies against the Company and the collateral securing the amounts due under the Term Loan. These events of default include, among other things, failure to pay any amounts due under the Term Loan, insolvency, the occurrence of a material adverse event, the occurrence of any default under certain other indebtedness and a final judgment against the Company in an amount greater than $0.3 million. During the years ended December 31, 2019 and 2018 the Company was in compliance with all covenants under the Term Loan. The Company has estimated that the risk of subjective acceleration under the material adverse events clause is reasonably possible, however not probable and therefore have classified the outstanding principal in current and long-term liabilities based on contractually scheduled principal payments. However, the assessment of such probability of the debt holder calling the debt is subjective and their actions and/or the Company’s related assessment could change in the future, which in turn would impact the classification of the debt balances.

Based on its current operating plans, the Company believes its cash, cash equivalents and marketable securities of $70.3 million as of December 31, 2019 will be sufficient to fund its anticipated level of operations, capital expenditures and satisfy debt repayments for a period of at least 12 months from the issuance date of this Annual Report. Until such time, if ever, as the Company can generate substantial product revenue, the Company expects to finance its cash needs through a combination of equity offerings, debt financings, collaborations, strategic alliances, licensing arrangements and other sources of funding. The Company expects to generate operating losses for the foreseeable future. If the Company is unable to raise additional funds through equity or debt financings, the Company may be required to delay, limit, reduce or terminate product development or future commercialization efforts or grant rights to develop and market products or product candidates that the Company would otherwise prefer to develop and market itself.

The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries Zafgen Securities Corporation, Zafgen Australia Pty Limited, Zafgen Animal Health, LLC. and Zordich Merger Sub, Inc. All intercompany balances and transactions have been eliminated.

The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($)			12 Months Ended		170 Months Ended
	Dec. 17, 2019	Jul. 02, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 29, 2017
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Entity incorporation date			Nov. 22, 2005
Restructuring and other attrition, percentage of workforce reduction			70.00%
Merger agreement minimum required net cash thresholds	$ 30,000,000
Accumulated deficit			$ (396,351,000)	$ (350,945,000)	$ (396,351,000)
Net proceeds from sale of securities					397,900,000
Net proceeds from public offering, after underwriting discount, commission and offering expenses				64,860,000
Credit facility default amount			300,000		300,000
Total cash, cash equivalents and marketable securities			70,300,000		70,300,000
Term Loan [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Aggregate principal balance			14,500,000		14,500,000	$ 20,000,000
Loan agreement minimum liquidity required			15,300,000	$ 21,000,000	15,300,000
Public Offering [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Issuance of common stock		9,200,000
Share price per share		$ 7.50
Net proceeds from public offering, after underwriting discount, commission and offering expenses		$ 64,600,000
Minimum [Member] \| Term Loan [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Total cash, cash equivalents and marketable securities			$ 55,000,000		$ 55,000,000
Chondrial Security Holders [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Percentage of expected diluted common shares immediately after merger	60.00%
Company Stockholders Prior to Merger [Member] \| Chondrial Security Holders [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Percentage of expected diluted common shares immediately after merger	40.00%
Chondrial Therapeutics Inc. [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Date of merger agreement	Dec. 17, 2019
Merger agreement termination fee to be paid by either party to other party upon termination of agreement	$ 3,375,000
Merger agreement minimum required net cash thresholds	$ 0
Beneficiary interest percentage in outstanding common stock	9.70%
Chondrial Therapeutics Inc. [Member] \| Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Additional third party expenses to be paid by either party to other party upon termination of merger agreement	$ 350,000

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

11. Income Taxes

During the years ended December 31, 2019, 2018 and 2017, the Company recorded no income tax benefits for the net operating losses incurred in each year due to its uncertainty of realizing a benefit from those items.

The domestic and foreign components of loss before income taxes are as follows:

	Year Ended December 31,
	2019			2018			2017
	(in thousands)
Domestic	$	(45,205	)	$	(58,708	)	$	(49,954	)
Foreign		(201	)		(2,660	)		(2,074	)
Loss before income taxes	$	(45,406	)	$	(61,368	)	$	(52,028	)

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2019			2018			2017
Federal statutory income tax rate	(21.0%)			(21.0%)			(34.0%)
Federal and state research and development tax credit		(4.1	)		(4.2	)	(4.1)
State taxes, net of federal benefit		(4.7	)		(3.7	)	(2.4)
Stock compensation expense		5.5			5.1			1.5
Nondeductible Australia research and development expenses		0.1			0.9			1.4
Impact of federal rate change related to tax reform		0.0			0.0			65.2
Other items		0.2			0.0			1.2
Change in deferred tax asset valuation allowance		24.0			22.9		(28.8)
Effective income tax rate		0.0	%		0.0	%		0.0	%

Net deferred tax assets as of December 31, 2019 and 2018 consisted of the following:

	December 31,
	2019			2018
	(in thousands)
Noncurrent deferred tax assets:
Capitalized research and development expenses	$	65,994		$	58,832
Net operating loss carryforwards		19,763			16,728
Tax credit carryforwards		21,202			19,331
Capitalized legal expenses		2,122			1,918
Stock-based compensation		3,242			4,371
Accrued expenses		276			493
Other temporary differences		18			19
Operating lease liability		1,752			—
Total noncurrent deferred tax assets		114,369			101,692
Total gross deferred tax assets		114,369			101,692

Noncurrent deferred tax liability:
Operating lease right-of-use assets		(1,790	)		—

Valuation allowance		(112,579	)		(101,692	)
Net deferred tax assets	$	—		$	—

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2019, 2018 and 2017 related primarily to changes in net operating loss carryforwards, capitalized research and development expenses and tax credit carryforwards and were as follows:

	Year Ended December 31,
	2019		2018		2017
	(in thousands)
Valuation allowance as of beginning of year	$	101,692	$	87,681	$	97,720
Decreases recorded as benefit to income tax provision		—		—		(10,039	)
Increases recorded to income tax provision		10,887		14,011		—
Valuation allowance as of end of year	$	112,579	$	101,692	$	87,681

As of December 31, 2019, the Company had net operating loss carryforwards that expire for federal and state income tax purposes of $55.7 million and $57.0 million, respectively, which begin to expire in 2026 and 2030, respectively. As of December 31, 2019, the Company had net operating loss carryforwards that were generated after December 31, 2017 of $21.2 million that do not expire, but the carryforwards are limited to 80% of the taxable income in any one tax period. As of December 31, 2019, the Company also had available tax credit carryforwards for federal and state income tax purposes of $17.9 million and $4.2 million, respectively, which begin to expire in 2026 and 2022, respectively. Utilization of the net operating loss carryforwards and tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income.

In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position.

For fiscal years through December 31, 2019, the Company generated research credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company’s research and development tax credit carry forwards; however, until a study is completed, and any adjustment is known, no amounts are being presented as an uncertain tax position as of December 31, 2019 or 2018. A full valuation allowance has been provided against the Company’s research and development tax credit carryforwards and, if an adjustment were to be required, this adjustment would be offset by a corresponding reduction to the valuation allowance.

As of December 31, 2019 and 2018, the Company’s net deferred tax asset balance before the valuation allowance was $112.6 million and $101.7 million, respectively, and was comprised principally of net operating loss carryforwards, capitalized research and development expenses and tax credit carryforwards. During the years ended December 31, 2019, 2018 and 2017, gross deferred tax assets increased due to additional net operating loss carryforwards, research and development tax credits generated and additional research and development expenses capitalized for tax purposes and the effects of tax reform.

The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of December 31, 2019 and 2018. Management reevaluates the positive and negative evidence at each reporting period.

The Company has not recorded any amounts for unrecognized tax benefits as of December 31, 2019 and 2018.

The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending income tax examinations. The Company’s tax years are still open under statute from 2015 to the present. Earlier years may be examined to the extent that tax credit or net operating loss carryforwards are used in future periods. The Company’s policy is to record interest and penalties related to income taxes as part of its income tax provision.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

10. Commitments and Contingencies

Leases

On February 12, 2019, the Company entered into a lease with Shigo Center Plaza Owners, LLC, for approximately 17,705 square feet of office space for a new headquarters located at 3 Center Plaza, Boston, Massachusetts. The lease has a term of 124 months with an option to extend the lease for 60 additional months. As part of the agreement the Company is required to maintain a letter of credit, which upon signing was $1.3 million and is classified as restricted cash within the consolidated financial statements. Under the lease agreement, the Company began paying monthly rent beginning four months after the lease commencement, which was June 21, 2019, with total lease payments over the initial term of $10.7 million. During the fourth quarter of 2019 and in conjunction with entering into a merger agreement with Chondrial, the Company performed an impairment review of the Company’s headquarters lease and related assets and determined that an impairment had not occurred as the estimated fair value of the asset exceeded the carrying value.

The Company’s prior headquarters lease was terminated, effective as of June 30, 2019.

In March 2015, the Company entered into an operating lease for office space in Boston, Massachusetts, effective as of April 15, 2015, with a term expiring on July 31, 2020, and an option to extend this lease for three additional years. In addition, with the landlord’s consent, the Company has subleased 2,976 square feet of office space in Boston, Massachusetts to an unrelated third party beginning on January 1, 2017 and expiring on July 31, 2020, and the Company expects to receive approximately $0.1 million in sublease rental income from January 1, 2020 through the end of the sublease term.

In October 2015, the Company entered into an operating lease for office space in San Diego, California, effective as of October 1, 2015, with a term extended to expire on December 31, 2024. Following the restructuring announced in September 2019, the Company recorded a $0.1 million impairment loss on Operating lease right-of-use asset.

Future minimum lease payments for its operating leases for the next five years and thereafter as of December 31, 2019 are as follows:

Year Ending December 31,	Operating
(in thousands)	Leases
2020		1,090
2021		1,120
2022		1,143
2023		1,165
2024		1,189
Thereafter		5,396
Total lease payments		11,103
Less: imputed interest		(4,261	)
Present value of lease liabilities	$	6,842

Under the prior lease guidance minimum rental commitments under non-cancelable leases for each of the next five years and thereafter as of December 31, 2018, were as follows:

Year Ending December 31,	Operating
(in thousands)	Leases
2019	$	464
2020		226
2021		—
2022		—
2023		—
2024		—
Thereafter		—
Total lease payments	$	690

During the year ended December 31, 2019 we incurred $0.6 million of lease expense associated with research and development and $0.4 million of lease expense associated with general and administrative activities. The components of lease expense are as follows:

	Year Ended
	December 31,
	2019
	(in thousands)
Operating lease cost	$	971
Short-term lease cost		185
Sublease income		(112	)
Total lease cost	$	1,044

During the years ended December 31, 2018, and 2017 the Company recognized $0.4 million and $0.3 million, respectively, of rental expense related to office space.

The weighted average remaining lease term and weighted average discount rate of our operating leases are as follows:

	As of December 31,
	2019
Weighted average remaining lease term in years		9.49
Weighted average discount rate		11.1	%

Supplemental cash flow information related to leases was as follow:

	Year Ended
	December 31,
	2019
	(in thousands)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	409
Investing cash flows from operating leases		586
Right-of-use assets obtained in exchange for lease obligations:
Operating leases		6,817

Intellectual Property Licenses

The Company has acquired exclusive rights to develop patented compounds and related know-how for beloranib under two licensing agreements with two third parties in the course of its research and development activities. The licensing rights obligate the Company to make payments to the licensors for license fees, milestones, license maintenance fees and royalties. The Company is also responsible for patent prosecution costs.

As of December 31, 2019, the Company is obligated to make additional milestone payments of up to $12.3 million upon reaching certain pre-commercialization milestones, such as clinical trials and government approvals (including the U.S. Food and Drug Administration, or “FDA”, approval of a New Drug application, or “NDA”), and up to $12.5 million upon reaching certain product commercialization milestones related to the development of beloranib. Under one of the license agreements, the Company is also obligated to pay up to $1.3 million with respect to each subsequent licensed product, if any, that is a new chemical entity. In addition, the Company will owe single-digit royalties on sales of commercial products developed using these licensed technologies, if any.

There were no milestones achieved during the years ended December 31, 2019, 2018 or 2017. The Company is also obligated to pay to the licensors a percentage of fees received if and when the Company sublicenses the technology. As of December 31, 2019, the Company has not yet developed a commercial product using the licensed technologies and it has not entered into any sublicense agreements for the technologies.

During the fourth quarter of 2019 the Company terminated the license agreement with Chong Kun Dang Pharmaceutical Corp. of South Korea (“CKD”) and provided written notice to Children’s Medical Center Corporation (“Children’s”), indicating that the agreement will be terminated by the end of the first quarter of 2020.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners, and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of management team and the board of directors of the Company that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any material claims as of December 31, 2019.

Legal Proceedings

The Company accrues a liability for legal contingencies when it believes that it is both probable that a liability has been incurred and that the Company can reasonably estimate the amount of the loss. The Company reviews these accruals and adjusts them to reflect ongoing negotiations, settlements, rulings, advice of legal counsel and other relevant information. To the extent new information is obtained and the views on the probable outcomes of claims, suits, assessments, investigations or legal proceedings change, changes in the Company’s accrued liabilities would be recorded in the period in which such determination is made. In addition, in accordance with the relevant authoritative guidance, for any matters in which the likelihood of material loss is at least reasonably possible, the Company will provide disclosure of the possible loss or range of loss. If a reasonable estimate cannot be made, however, the Company will provide disclosure to that effect. The Company expenses legal costs as they are incurred.

The Company may periodically become subject to other legal proceedings and claims arising in connection with ongoing business activities, including claims or disputes related to patents that have been issued or that are pending in the field of research on which the Company is focused. The Company is not aware of any material claims as of December 31, 2019.

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2019
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities as of the date of the consolidated financial statements, and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
Cash Equivalents	Cash Equivalents The Company considers all short-term, highly liquid investments with original maturities of ninety days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market funds, U.S. government securities, corporate bonds, and commercial paper, are stated at fair value.
Concentration of Credit Risk and of Significant Suppliers	Concentration of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company has all cash, cash equivalents and marketable securities balances at accredited financial institutions in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs, if and when development programs are active. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.
Marketable Securities	Marketable Securities Marketable securities consist of investments with original maturities greater than ninety days. The Company has classified its investments with maturities beyond one year as short term, based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. The Company classifies its marketable securities as available-for-sale. Accordingly, these investments are recorded at fair value, which is based on quoted market prices. Unrealized gains and losses are reported as a component of accumulated other comprehensive loss in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other income (expense), net, based on the specific identification method. When determining whether a decline in value is other than temporary, the Company considers various factors, including whether the Company has the intent to sell the security, and whether it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis. Fair value is determined based on quoted market prices.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes certain legal, accounting and other third-party fees that are directly associated with in-process equity financings as other assets until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity as a reduction of additional paid-in capital generated as a result of the offering or as a reduction to the carrying value of preferred stock issued.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over a three or five-year estimated useful life for equipment, furniture and fixtures and office equipment. Leasehold improvements are amortized over the shorter of the asset life or the term of the lease agreement. Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment, net¸and the net operating lease asset. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. Any impairment loss, if indicated, is measured as the amount by which the carrying amount of the asset exceeds the estimated fair value of the asset. To date, the Company has recorded $0.1 million impairment losses on long-lived assets associated with the restructuring announced in September 2019.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Included in research and development expenses are wages, stock-based compensation and benefits of employees, third-party license fees and milestones and other operational costs related to the Company’s research and development activities, including facility-related expenses and external costs of outside vendors engaged to conduct nonclinical studies, manufacturing activities, and clinical trials. The Company records research and development expenses net of any research and development tax incentives the Company is entitled to receive from government authorities.
Research Contract Costs and Accruals	Research Contract Costs and Accruals The Company has, from time to time, entered into various research and development contracts with research institutions and other companies both inside and outside of the United States. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.
Patent Costs	Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are recorded as general and administrative expenses as incurred, as recoverability of such expenditures is uncertain.
Accounting for Stock-Based Compensation	Accounting for Stock-Based Compensation The Company measures all stock-based awards granted to employees, non-employee consultants and directors based on the fair value on the date of grant using the Black-Scholes option-pricing model. Compensation expense of those awards is recognized over the requisite service period, which is generally the vesting period of the respective award. Typically, the Company issues awards with only service-based and market-based vesting conditions and records the expense for these awards using the straight-line method. The Company accounts for forfeitures as they occur. The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.
Segment Data	Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company is a biopharmaceutical company that has leveraged its proprietary knowledge of the MetAP2 pathway to pioneer the study of MetAP2 inhibitors in both common and rare metabolic disorders. No revenue has been generated since inception, and all tangible assets are held in the United States.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2019, 2018 and 2017, the Company’s only element of other comprehensive income was unrealized gain on marketable securities.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of common shares, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common shares, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is antidilutive.
Recently Issued and Adopted Accounting Pronouncements	Recently Issued and Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (the “FASB”) issued ASU No. 2016-02, Leases and in July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. The new leasing standards generally require lessees to recognize operating and financing lease liabilities and corresponding right-of-use assets on the consolidated balance sheet and to provide enhanced disclosures surrounding the amount, timing and uncertainty of cash flows arising from leasing arrangements. We adopted the new leasing standards using the modified retrospective transition approach, as of January 1, 2019, with no restatement of prior periods or cumulative adjustment to retained earnings. Upon adoption, we elected the package of transition practical expedients, which allowed us to carry forward prior conclusions related to whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases and initial direct costs for existing leases. In addition, the Company elected the hindsight practical expedient to determine the lease term for existing leases. The Company elected not to record leases with an initial term of 12 months or less on the balance sheet and recognize the associated lease payments in the consolidated statements of operations on a straight-line basis over the lease term. Upon adoption of the new leasing standards we recognized an operating lease asset of approximately $1.0 million and a corresponding operating lease liability of approximately $1.0 million, which are included in our consolidated balance sheet. The adoption of the new leasing standards did not have an impact on our consolidated statements of income or cash flows. We determine if an arrangement is a lease at contract inception. Operating lease assets represent our right to use an underlying asset for the lease term and operating lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease assets and liabilities are recognized at the commencement date of the lease based upon the present value of lease payments over the lease term. When determining the lease term, we include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. We use the implicit rate when readily determinable and use our incremental borrowing rate when the implicit rate is not readily determinable based upon the information available at the commencement date in determining the present value of the lease payments. Our incremental borrowing rate is determined using a secured borrowing rate for the same currency and term as the associated lease. The lease payments used to determine our operating lease assets may include lease incentives, stated rent increases and escalation clauses linked to rates of inflation when determinable and are recognized in our operating lease assets in our consolidated balance sheets. Our operating leases are reflected in operating lease right-of-use assets, short-term operating lease liabilities and in long-term operating lease liabilities in our consolidated balance sheets. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. For additional information on the adoption of the new leasing standards, please read Note 10, Commitments and Contingencies, to these consolidated financial statements. In June 2018, the FASB issued ASU No. 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. This ASU is intended to simplify aspects of share-based compensation issued to non-employees by making the guidance consistent accounting for employee share-based compensation. This standard was effective for the Company in 2019. The adoption of this guidance had an immaterial impact on the Company’s consolidated financial statements as of and for the year ended December 31, 2019. In August 2018 the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. This standard modifies certain disclosure requirements on fair value measurements. This standard became effective for the Company on January 1, 2020. The adoption of this standard will not have a material impact on the Company’s disclosures.

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0
Operating expenses:
Research and development	23,886	47,929	40,839
General and administrative	16,215	13,193	12,160
Restructuring charges	5,553
Total operating expenses	45,654	61,122	52,999
Loss from operations	(45,654)	(61,122)	(52,999)
Other income (expense):
Interest income	1,989	1,889	996
Interest expense	(1,766)	(1,898)	(165)
Foreign currency transaction gains (losses), net	25	(237)	140
Total other income (expense), net	248	(246)	971
Net loss	$ (45,406)	$ (61,368)	$ (52,028)
Net loss per share, basic and diluted	$ (1.22)	$ (1.90)	$ (1.90)
Weighted average common shares outstanding, basic and diluted	37,347,199	32,228,721	27,433,239
Comprehensive loss:
Net loss	$ (45,406)	$ (61,368)	$ (52,028)
Other comprehensive income:
Unrealized gain on marketable securities	68	25	22
Total other comprehensive income	68	25	22
Total comprehensive loss	$ (45,338)	$ (61,343)	$ (52,006)

Income Taxes - Reconciliation of Federal Statutory Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	(21.00%)	(21.00%)	(34.00%)
Federal and state research and development tax credit	(4.10%)	(4.20%)	(4.10%)
State taxes, net of federal benefit	(4.70%)	(3.70%)	(2.40%)
Stock compensation expense	5.50%	5.10%	1.50%
Nondeductible Australia research and development expenses	0.10%	0.90%	1.40%
Impact of federal rate change related to tax reform	(0.00%)	(0.00%)	65.20%
Other items	0.20%	(0.00%)	1.20%
Change in deferred tax asset valuation allowance	24.00%	22.90%	(28.80%)
Effective income tax rate	0.00%	0.00%	0.00%

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Computation of Basic and Diluted Earnings Per Share

Basic and diluted net loss per share was calculated as follows:

	Year Ended December 31,
	2019			2018			2017
	(in thousands, except per share data)
Basic and diluted net loss per share:
Numerator:
Net loss	$	(45,406	)	$	(61,368	)	$	(52,028	)
Denominator:
Weighted average common shares outstanding, basic and diluted		37,347,199			32,228,721			27,433,239
Net loss per share, basic and diluted	$	(1.22	)	$	(1.90	)	$	(1.90	)

Summary of Common Stock Equivalents Outstanding

The Company excluded the following common stock equivalents outstanding as of December 31, 2019, 2018 and 2017 from the computation of diluted net loss per share for the years ended December 31, 2019, 2018 and 2017 because they had an anti-dilutive impact due to the net loss incurred for the periods:

	As of December 31,
	2019		2018		2017
Options to purchase common stock		3,964,707		5,024,371		4,494,201
Restricted stock units		49,136		—		—
		4,013,843		5,024,371		4,494,201

Fair Value Measurements and Marketable Securities

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements and Marketable Securities

3. Fair Value Measurements and Marketable Securities

Fair Value Measurements

The following tables present information about the Company’s financial assets that have been measured at fair value as of December 31, 2019 and 2018 and indicate the fair value of the hierarchy of the valuation inputs utilized to determine such fair value. In general, fair values determined by Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities. Fair value determined by Level 2 inputs utilize observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted market prices in markets that are not active or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities. Fair values determined by Level 3 inputs are unobservable data points for the asset or liability, and include situations where there is little, if any, market activity for the asset or liability. During the years ended December 31, 2019 and 2018, there were no transfers between Level 1 and Level 2 financial assets.

The following tables summarize the Company’s cash equivalents and marketable securities as of December 31, 2019 and 2018:

	December 31, 2019
			Quoted		Significant
			Prices in		Other			Significant
			Active		Observable			Unobservable
			Markets		Inputs			Inputs
	Total		(Level 1)		(Level 2)			(Level 3)
	(in thousands)
Cash equivalents:
Money market funds	$	18,289	$	18,289	$	—	$		—
U.S. Government securities		3,098		—		3,098			—
Commercial paper		1,047		—		1,047			—
Total cash equivalents		22,434		18,289		4,145			—
Marketable securities:
U.S. Government securities		14,996		—		14,996			—
Corporate bonds		14,648		—		14,648			—
Commercial paper		13,406		—		13,406			—
Total marketable securities		43,050		—		43,050			—
Total cash equivalents and marketable securities	$	65,484	$	18,289	$	47,195		$	—

	December 31, 2018
			Quoted		Significant
			Prices in		Other		Significant
			Active		Observable		Unobservable
			Markets		Inputs		Inputs
	Total		(Level 1)		(Level 2)		(Level 3)
	(in thousands)
Cash equivalents:
Money market funds	$	40,231	$	40,231	$	—	$	—
Commercial paper		4,979		—		4,979		—
Total cash equivalents		45,210		40,231		4,979		—
Marketable securities:
Commercial paper		38,911		—		38,911		—
Corporate bonds		25,830		—		25,830		—
U.S. Government securities		3,994		—		3,994		—
Total marketable securities		68,735		—		68,735		—
Total cash equivalents and marketable securities	$	113,945	$	40,231	$	73,714	$	—

The carrying amounts reflected in the consolidated balance sheets for tax incentive receivable, accounts payable, and accrued expenses approximate fair value due to their short-term maturities. The carrying value of the Company’s outstanding notes payable approximates fair value (a Level 2 fair value measurement), reflecting interest rates currently available to the Company.

Marketable Securities

The following tables summarize the Company’s marketable securities as of December 31, 2019 and 2018:

	December 31, 2019
			Gross		Gross
	Amortized		Unrealized		Unrealized
	Cost		Gains		Losses		Fair Value
	(in thousands)
Assets:
U.S. Government securities (due within 1 year)	$	14,981	$	15	$	—	$	14,996
Corporate bonds (due within 1 year)		14,628		20		—		14,648
Commercial paper (due within 1 year)		13,406		—		—		13,406
	$	43,015	$	35	$	—	$	43,050

	December 31, 2018
			Gross		Gross
	Amortized		Unrealized		Unrealized
	Cost		Gains		Losses			Fair Value
	(in thousands)
Assets:
Commercial paper (due within 1 year)	$	38,921	$	—	$	(10	)	$	38,911
Corporate bonds (due within 1 year)		25,851		3		(24	)		25,830
U.S. Government securities (due within 1 year)		3,995		—		(1	)		3,994
	$	68,767	$	3	$	(35	)	$	68,735

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments for Operating Leases

Future minimum lease payments for its operating leases for the next five years and thereafter as of December 31, 2019 are as follows:

Year Ending December 31,	Operating
(in thousands)	Leases
2020		1,090
2021		1,120
2022		1,143
2023		1,165
2024		1,189
Thereafter		5,396
Total lease payments		11,103
Less: imputed interest		(4,261	)
Present value of lease liabilities	$	6,842

Under the prior lease guidance minimum rental commitments under non-cancelable leases for each of the next five years and thereafter as of December 31, 2018, were as follows:

Year Ending December 31,	Operating
(in thousands)	Leases
2019	$	464
2020		226
2021		—
2022		—
2023		—
2024		—
Thereafter		—
Total lease payments	$	690

Schedule of Components of Leases Expense

The components of lease expense are as follows:

	Year Ended
	December 31,
	2019
	(in thousands)
Operating lease cost	$	971
Short-term lease cost		185
Sublease income		(112	)
Total lease cost	$	1,044

Schedule of Weighted Average Remaining Lease Term and Weighted Average Discount Rate of Operating Leases

The weighted average remaining lease term and weighted average discount rate of our operating leases are as follows:

	As of December 31,
	2019
Weighted average remaining lease term in years		9.49
Weighted average discount rate		11.1	%

Schedule of Supplemental Cash Flow Information Related to Leases

Supplemental cash flow information related to leases was as follow:

	Year Ended
	December 31,
	2019
	(in thousands)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	409
Investing cash flows from operating leases		586
Right-of-use assets obtained in exchange for lease obligations:
Operating leases		6,817

Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2019

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity described above, since December 31, 2018:

	Shares			Weighted		Average
	Issuable			Average		Remaining	Aggregate
	Under			Exercise		Contractual	Intrinsic
	Options			Price		Term	Value
						(in years)	(in thousands)
Outstanding as of December 31, 2018		5,024,371		$	8.85	7.6	$	3,143
Granted		2,276,197		$	4.00
Exercised		(83,047	)	$	0.81
Forfeited		(3,252,814	)	$	8.81
Outstanding as of December 31, 2019		3,964,707		$	6.26	6.7	$	—
Options exercisable as of December 31, 2019		1,700,815		$	8.49	6.8	$	—

Summary of Restricted Stock Units Activity

				Weighted
				Average
				Grant Date
	Shares			Fair Value

Unvested at December 31, 2018		—		$	—
Granted		355,187		$	4.62
Vested		(15,267	)	$	4.38
Forfeited		(290,784	)	$	4.63
Unvested at December 31, 2019		49,136		$	4.63

Summary of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock

The Company recorded stock-based compensation expense related to stock options and restricted common stock in the following expense categories within its consolidated statements of operations:

	Year Ended December 31,
	2019		2018		2017
	(in thousands)
Research and development	$	1,322	$	5,476	$	4,138
General and administrative		4,175		4,151		4,163
	$	5,497	$	9,627	$	8,301

Options with Time-Based Vesting Conditions [Member]

Assumptions used to Determine Fair Value of Stock Options Granted

The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors are as follows, presented on a weighted average basis:

	2019			2018			2017
Risk-free interest rate		2.49	%		2.77	%		2.10	%
Expected term (in years)		6.17			6.17			6.17
Expected volatility		96	%		100	%		93	%
Expected dividend yield		0	%		0	%		0	%

Options with Market-Based Vesting Conditions [Member]

Assumptions used to Determine Fair Value of Stock Options Granted

The assumptions that the Company used to determine the fair value of the Price Target Options granted to employees were as follows, presented on a weighted average basis:

	2017
Risk-free interest rate		2.24	%
Expected term (in years)		6.30
Expected volatility		95	%
Expected dividend yield		0	%

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (45,406)	$ (61,368)	$ (52,028)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	5,497	9,627	8,301
Non-cash interest expense			13
Depreciation expense	263	261	188
Impairment of assets	80
Loss on disposal of fixed assets	20
Unrealized foreign currency transaction losses (gains)	5	76	(46)
Premium on marketable securities, net	(69)	(6)	(359)
Amortization of (discount) premium on marketable securities	(788)	(670)	246
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	729	199	(569)
Tax incentive receivable	1,288	(666)	(553)
Accounts payable	(2,958)	432	448
Accrued restructuring costs	2,709
Accrued expenses and other	(2,190)	628	575
Other assets	37
Net cash used in operating activities	(40,783)	(51,487)	(43,784)
Cash flows from investing activities:
Proceeds from sales and maturities of marketable securities	109,471	110,388	150,213
Purchases of marketable securities	(82,861)	(117,147)	(114,511)
Purchases of property and equipment	(764)	(108)	(55)
Proceeds from sales of property and equipment	3
Payments for leasehold improvements on right-of-use assets	(586)
Net cash provided by (used in) investing activities	25,263	(6,867)	35,647
Cash flows from financing activities:
Proceeds from issuance of notes payable			20,000
Repayments of notes payable	(5,455)		(3,633)
Proceeds from exercise of common stock options and employee stock purchase plan	194	2,360	195
Proceeds from public offerings, net of commissions and underwriting discounts		64,860
Payments of public offering costs		(312)
Net cash (used in) provided by financing activities	(5,261)	66,908	16,562
Net (decrease) increase in cash, cash equivalents and restricted cash	(20,781)	8,554	8,425
Cash, cash equivalents and restricted cash at beginning of period	49,331	40,777	32,352
Cash, cash equivalents and restricted cash at end of period	28,550	49,331	40,777
Supplemental disclosure of non-cash investing and financing activities:
Public offering costs included in accounts payable		138
Right-of-use asset obtained in exchange for operating lease obligation	6,817
Supplemental disclosure of cash flow information:
Cash paid for interest	$ 1,217	$ 1,144	$ 141

Notes Payable - Additional Information (Detail) - USD ($)		12 Months Ended
	Dec. 29, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Proceeds from issuance of notes payable	$ 20,000,000			$ 20,000,000
Unrestricted cash, cash equivalents and marketable securities		$ 70,300,000
Credit facility default amount		300,000
Maximum [Member]
Debt Instrument [Line Items]
Aggregate value of cash maintained by Australian subsidiary, limit		4,000,000
Term Loan [Member]
Debt Instrument [Line Items]
Maximum borrowings under term loan	$ 20,000,000	$ 14,500,000
Debt facility description		Upon entering into this Term Loan, the Company is obligated to make monthly, interest-only payments until March 29, 2019 and, thereafter, to pay 33 consecutive, equal monthly installments of principal and interest from April 1, 2019 through December 1, 2021. The outstanding Term Loan bears a variable annual interest rate of 1.25% above the prime rate, which as of December 31, 2019 was 4.75%. In addition, a final payment equal to 8.0% of the Term Loan is due upon the earlier of the maturity date, acceleration of the Term Loan or prepayment of all or part of the Term Loan.
Debt maturity date	Dec. 01, 2021
Debt facility interest rate description		1.25% above the prime rate
Debt facility variable annual interest rate above prime rate	1.25%
Debt facility fee percentage	8.00%
Charges to interest expense of debt outstanding	$ 1,600,000
Debt facility effective annual interest rate		9.20%
Loan agreement minimum liquidity required		$ 15,300,000	$ 21,000,000
Debt facility covenant description		Further, as of 45 days after the Term Loan was entered in, the Company must maintain a balance of unrestricted cash, cash equivalents and marketable securities at Silicon Valley Bank in an amount not less than the greater of (i) $55.0 million and (ii) sixty-five percent (65%) of all the Company’s cash, cash equivalents and marketable securities. If the Company does not meet this requirement it will not be considered an event of default provided it immediately secures 87.5% of the principal balance in a restricted cash account
Percentage of principal balance to be secured in restricted cash account for not to be considered an event of default		87.50%
Interest expense on term loan		$ 1,800,000	$ 1,900,000
Term Loan [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Percentage equivalent of cash, cash equivalents and marketable securities balance		105.00%
Unrestricted cash, cash equivalents and marketable securities		$ 55,000,000
Percentage of cash, cash equivalents and marketable securities		65.00%
Term Loan [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest expense on term loan				100,000
Term Loan [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Debt facility prime annual interest rate		4.75%
Secured Debt [Member] \| 2014 Credit Facility [Member]
Debt Instrument [Line Items]
Interest expense on credit facility				$ 200,000

Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Schedule of Unaudited Consolidated Financial Statements

	Three Months Ended
	March 31,			June 30,			September 30,			December 31,
	2019			2019			2019			2019
	(in thousands, except per share data)
Revenue	$	—		$	—		$	—		$	—
Operating expenses		13,277			12,190			12,906			7,281
Net loss		(13,112	)		(12,129	)		(12,914	)		(7,251	)
Net loss per share, basic and diluted	$	(0.35	)	$	(0.32	)	$	(0.35	)	$	(0.19	)
Weighted average common shares outstanding, basic and diluted		37,313,947			37,326,853			37,369,829			37,377,223


	Three Months Ended
	March 31,			June 30,			September 30,			December 31,
	2018			2018			2018			2018
	(in thousands, except per share data)
Revenue	$	—		$	—		$	—		$	—
Operating expenses		15,702			15,560			15,169			14,691
Net loss		(15,956	)		(15,775	)		(15,067	)		(14,570	)
Net loss per share, basic and diluted	$	(0.58	)	$	(0.57	)	$	(0.41	)	$	(0.39	)
Weighted average common shares outstanding, basic and diluted		27,541,594			27,565,064			36,619,575			37,036,065

Income Taxes - Schedule of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Noncurrent deferred tax assets:
Capitalized research and development expenses	$ 65,994	$ 58,832
Net operating loss carryforwards	19,763	16,728
Tax credit carryforwards	21,202	19,331
Capitalized legal expenses	2,122	1,918
Stock-based compensation	3,242	4,371
Accrued expenses	276	493
Other temporary differences	18	19
Operating lease liability	1,752
Total noncurrent deferred tax assets	114,369	101,692
Total gross deferred tax assets	114,369	101,692
Noncurrent deferred tax liability:
Operating lease right-of-use assets	(1,790)
Valuation allowance	(112,579)	(101,692)	$ (87,681)	$ (97,720)
Net deferred tax assets	$ 0	$ 0

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Domestic and Foreign Components of Loss Before Income Taxes

The domestic and foreign components of loss before income taxes are as follows:

	Year Ended December 31,
	2019			2018			2017
	(in thousands)
Domestic	$	(45,205	)	$	(58,708	)	$	(49,954	)
Foreign		(201	)		(2,660	)		(2,074	)
Loss before income taxes	$	(45,406	)	$	(61,368	)	$	(52,028	)

Reconciliation of Federal Statutory Income Tax Rate

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2019			2018			2017
Federal statutory income tax rate	(21.0%)			(21.0%)			(34.0%)
Federal and state research and development tax credit		(4.1	)		(4.2	)	(4.1)
State taxes, net of federal benefit		(4.7	)		(3.7	)	(2.4)
Stock compensation expense		5.5			5.1			1.5
Nondeductible Australia research and development expenses		0.1			0.9			1.4
Impact of federal rate change related to tax reform		0.0			0.0			65.2
Other items		0.2			0.0			1.2
Change in deferred tax asset valuation allowance		24.0			22.9		(28.8)
Effective income tax rate		0.0	%		0.0	%		0.0	%

Schedule of Net Deferred Tax Assets

Net deferred tax assets as of December 31, 2019 and 2018 consisted of the following:

	December 31,
	2019			2018
	(in thousands)
Noncurrent deferred tax assets:
Capitalized research and development expenses	$	65,994		$	58,832
Net operating loss carryforwards		19,763			16,728
Tax credit carryforwards		21,202			19,331
Capitalized legal expenses		2,122			1,918
Stock-based compensation		3,242			4,371
Accrued expenses		276			493
Other temporary differences		18			19
Operating lease liability		1,752			—
Total noncurrent deferred tax assets		114,369			101,692
Total gross deferred tax assets		114,369			101,692

Noncurrent deferred tax liability:
Operating lease right-of-use assets		(1,790	)		—

Valuation allowance		(112,579	)		(101,692	)
Net deferred tax assets	$	—		$	—

Summary Changes in the Valuation Allowance for Deferred Tax Assets

	Year Ended December 31,
	2019		2018		2017
	(in thousands)
Valuation allowance as of beginning of year	$	101,692	$	87,681	$	97,720
Decreases recorded as benefit to income tax provision		—		—		(10,039	)
Increases recorded to income tax provision		10,887		14,011		—
Valuation allowance as of end of year	$	112,579	$	101,692	$	87,681

Notes Payable

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Notes Payable

6. Notes Payable

On December 29, 2017, the Company entered into a loan and security agreement with Silicon Valley Bank (the “Term Loan”). The Term Loan provided for borrowings of $20.0 million. On December 29, 2017, the Company received proceeds of $20.0 million from the issuance of a promissory note. The promissory note issued under the Term Loan is collateralized by substantially all of the Company’s personal property, other than its intellectual property.

Upon entering into this Term Loan, the Company is obligated to make monthly, interest-only payments until March 29, 2019 and, thereafter, to pay 33 consecutive, equal monthly installments of principal and interest from April 1, 2019 through December 1, 2021. The outstanding Term Loan bears a variable annual interest rate of 1.25% above the prime rate, which as of December 31, 2019 was 4.75%. In addition, a final payment equal to 8.0% of the Term Loan is due upon the earlier of the maturity date, acceleration of the Term Loan or prepayment of all or part of the Term Loan. The Company accrues the final payment amount of $1.6 million, to outstanding debt by charges to interest expense using the effective-interest method from the date of issuance through the maturity date. The effective annual interest rate of the outstanding debt under the Term Loan is approximately 9.2% as of December 31, 2019.

Additionally, the Company, as the borrower, is required to maintain a minimum cash, cash equivalents and marketable securities balance at Silicon Valley Bank of no less than 105% of the total outstanding principal balance of the Term Loan, which as of December 31, 2019 was $15.3 million and as of December 31, 2018 was $21.0 million.

Further, as of 45 days after the Term Loan was entered in, the Company must maintain a balance of unrestricted cash, cash equivalents and marketable securities at Silicon Valley Bank in an amount not less than the greater of (i) $55.0 million and (ii) sixty-five percent (65%) of all the Company’s cash, cash equivalents and marketable securities. If the Company does not meet this requirement it will not be considered an event of default provided it immediately secures 87.5% of the principal balance in a restricted cash account.

There are negative covenants restricting the Company’s activities, including limitations on dispositions, mergers or acquisitions; encumbering or granting a security interest in its intellectual property; incurring indebtedness or liens; paying dividends; making certain investments; permitting the aggregate value of cash maintained by its Australian subsidiary not to exceed $4.0 million and certain other business transactions.

The Term Loan also includes events of default, the occurrence and continuation of any of which provides the lenders the right to exercise remedies against the Company and the collateral securing the amounts due under the Term Loan, including cash in the amount of the outstanding balance. These events of default include, among other things, failure to pay any amounts due under the Term Loan, insolvency, the occurrence of a material adverse event, the occurrence of any default under certain other indebtedness and a final judgment against the Company in an amount greater than $0.3 million. During the years ended December 31, 2019 and 2018 the Company was in compliance with all covenants under the Term Loan.

The Company has estimated that the risk of subjective acceleration under the material adverse events clause is reasonably possible, however not probable and therefore have classified the outstanding principal in current and long-term liabilities based on contractually scheduled principal payments. However, the assessment of such probability of the debt holder calling the debt is subjective and their actions and/or the Company’s related assessment could change in the future, which in turn would impact the classification of the debt balances.

As of December 31, 2019 and 2018, notes payable consist of the following:

	December 31,
	2019			2018
	(in thousands)
Notes payable	$	14,545		$	20,000
Less: current portion		(7,273	)		(5,455	)
Notes payable, net of current portion		7,272			14,545
Accretion related to final payment		1,192			640
Notes payable, long term	$	8,464		$	15,185

As of December 31, 2019, the estimated future principal payments due are as follows:

Year Ending December 31,
(in thousands)
2020	$	7,273
2021		7,272
	$	14,545

During the years ended December 31, 2019, 2018 and 2017, the Company recognized $1.8 million, $1.9 million and less than $0.1 million, respectively, of interest expense related to the Term Loan. During the year ended December 31, 2017, the Company recognized $0.2 million of interest expense related to the 2014 Credit Facility.

Commitments and Contingencies - Schedule of Weighted Average Remaining Lease Term and Weighted Average Discount Rate of Operating Leases (Detail)	Dec. 31, 2019
Leases [Abstract]
Weighted average remaining lease term in years	9 years 5 months 26 days
Weighted average discount rate	11.10%

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued payroll and related expenses	$ 37	$ 2,291
Accrued research and development expenses		1,526
Accrued professional fees	864	221
Accrued other	289	223
Total accrued expenses and other	$ 1,190	$ 4,261

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
Impairment losses on long-lived assets	$ 100
Percentage of likelihood to be realized upon ultimate settlement, description	50.00%
Operating lease asset	$ 7,051
Operating lease liability	$ 6,456
ASU 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating lease asset		$ 1,000
Operating lease liability		$ 1,000
Equipment, Furniture and Fixtures and Office Equipment [Member] \| Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life	3 years
Equipment, Furniture and Fixtures and Office Equipment [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life	5 years

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value per share	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share	$ 0.001	$ 0.001
Common stock, shares authorized	115,000,000	115,000,000
Common stock, shares issued	37,446,498	37,287,221
Common stock, shares outstanding	37,446,498	37,287,221

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes Disclosure [Line Items]
Income tax benefit	$ 0	$ 0	$ 0
Operating loss carryforwards, minimum percentage of taxable income in tax period	80.00%
Operating loss carryforwards, description	carryforwards are limited to 80% of the taxable income in any one tax period.
Uncertain tax position	$ 0	0
Net deferred tax assets before the valuation allowance	112,600,000	101,700,000
Unrecognized tax benefits	0	$ 0
No Expiration [Member]
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards	$ 21,200,000
Earliest Tax Year [Member]
Income Taxes Disclosure [Line Items]
Open tax year	2015
Domestic Tax Authority [Member]
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards	$ 55,700,000
Net operating loss carryforwards, beginning of expiration period	2026
Tax credit carryforward	$ 17,900,000
Research and development tax credit carry forwards, beginning of expiration period	2026
State and Local Jurisdiction [Member]
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards	$ 57,000,000
Net operating loss carryforwards, beginning of expiration period	2030
Tax credit carryforward	$ 4,200,000
Research and development tax credit carry forwards, beginning of expiration period	2022

Restructuring - Summary of Restructuring Charges by Category (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Restructuring Cost And Reserve [Line Items]
Restructuring charges	$ 5,553
Cash [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	5,473
Non-Cash [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	80
Research and Development [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	5,118
Research and Development [Member] \| Cash [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	5,038
Research and Development [Member] \| Non-Cash [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	80
General and Administrative [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	435
General and Administrative [Member] \| Cash [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	$ 435

Restructuring - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) Employee
Restructuring And Related Activities [Abstract]
Number of workforce reduction \| Employee	20
Restructuring charges and related costs	$ 5,553
Restructuring charges paid	2,764
Accrued restructuring costs	$ 2,709

Commitments and Contingencies - Schedule of Future Minimum Lease Payments for Operating Leases (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Leases [Abstract]
2020	$ 1,090
2021	1,120
2022	1,143
2023	1,165
2024	1,189
Thereafter	5,396
Total lease payments	11,103
Less: imputed interest	(4,261)
Present value of lease liabilities	$ 6,842

Net Loss Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss	$ (7,251)	$ (12,914)	$ (12,129)	$ (13,112)	$ (14,570)	$ (15,067)	$ (15,775)	$ (15,956)	$ (45,406)	$ (61,368)	$ (52,028)
Denominator:
Weighted average common shares outstanding, basic and diluted	37,377,223	37,369,829	37,326,853	37,313,947	37,036,065	36,619,575	27,565,064	27,541,594	37,347,199	32,228,721	27,433,239
Net loss per share, basic and diluted	$ (0.19)	$ (0.35)	$ (0.32)	$ (0.35)	$ (0.39)	$ (0.41)	$ (0.57)	$ (0.58)	$ (1.22)	$ (1.90)	$ (1.90)

Commitments and Contingencies - Schedule of Future Minimum Rental Commitments under Prior Lease Guidance (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 464
2020	226
Total lease payments	$ 690

Notes Payable - Schedule of Notes Payable (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instruments [Abstract]
Notes payable	$ 14,545	$ 20,000
Less: current portion	(7,273)	(5,455)
Notes payable, net of current portion	7,272	14,545
Accretion related to final payment	1,192	640
Notes payable, long term	$ 8,464	$ 15,185

Commitments and Contingencies - Schedule of Supplemental Cash Flow Information Related to Leases (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 409
Investing cash flows from operating leases	586
Right-of-use assets obtained in exchange for lease obligations:
Operating leases	$ 6,817

Notes Payable - Schedule of Estimated Future Principal Payments (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Debt Instruments [Abstract]
2020	$ 7,273
2021	7,272
Long-term Debt	$ 14,545

Fair Value Measurements and Marketable Securities - Summary of Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 43,015	$ 68,767
Gross Unrealized Gains	35	3
Gross Unrealized Losses		(35)
Fair Value	43,050	68,735
U.S. Government Securities (Due within 1 Year) [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,981	3,995
Gross Unrealized Gains	15
Gross Unrealized Losses		(1)
Fair Value	14,996	3,994
Corporate Bonds (Due within 1 Year) [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,628	25,851
Gross Unrealized Gains	20	3
Gross Unrealized Losses		(24)
Fair Value	14,648	25,830
Commercial Paper (Due within 1 Year) [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,406	38,921
Gross Unrealized Losses		(10)
Fair Value	$ 13,406	$ 38,911

Property and Equipment, Net - Schedule of Property Plant and Equipment Net (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,564	$ 925
Less: Accumulated depreciation	(743)	(550)
Property and equipment, net	821	375
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 364	348
Office Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Useful Life	3 years
Office Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Useful Life	5 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Useful Life	5 years
Property and equipment, gross	$ 801	156
Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Useful Life	5 years
Property and equipment, gross		6
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 399	$ 415

Stockholders' Equity - Additional Information (Detail) - USD ($)			12 Months Ended
	Nov. 09, 2018	Jul. 02, 2018	Dec. 31, 2019	Dec. 31, 2018
Proceeds from offering, net of commissions and underwriting discounts				$ 64,860,000
Preferred stock, shares authorized			5,000,000	5,000,000
Preferred stock, par value			$ 0.001	$ 0.001
Common stock, shares authorized			115,000,000	115,000,000
Common stock, par value			$ 0.001	$ 0.001
Common Stock [Member]
Issuance of common stock				9,200,000
Public Offering [Member]
Issuance of common stock		9,200,000
Share price per share		$ 7.50
Proceeds from offering, net of commissions and underwriting discounts		$ 64,600,000
ATM Offering Program [Member] \| Cowen [Member]
Sales agreement, description			The Company has no obligation to sell any shares under the Sales Agreement, and may at any time suspend solicitation and offers under the Sales Agreement.
ATM Offering Program [Member] \| Cowen [Member] \| Common Stock [Member]
Issuance of common stock			0
Percentage of compensation for services equal to gross proceeds	3.00%
ATM Offering Program [Member] \| Cowen [Member] \| Common Stock [Member] \| Maximum [Member]
Aggregate gross sales proceeds under sales agreement	$ 50,000,000