Allena Pharmaceuticals (ALNAQ) 10-K 16 Mar 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Mar. 06, 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
Trading Symbol	ALNA
Entity Registrant Name	Allena Pharmaceuticals, Inc.
Entity Central Index Key	0001624658
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		24,742,146
Entity Public Float			$ 93,291,474
Entity Interactive Data Current	Yes
Document Annual Report	true
Document Transition Report	false
Entity File Number	001-38268
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	45-2729920
Entity Address, Address Line One	One Newton Executive Park
Entity Address, Address Line Two	Suite 202
Entity Address, City or Town	Newton
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02462
City Area Code	617
Local Phone Number	467-4577
Title of 12(b) Security	Common Stock, par value $0.001 per share
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.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 30,007	$ 61,643
Prepaid expenses and other current assets	3,028	2,826
Total current assets	33,035	64,469
Property and equipment, net	401	514
Operating lease assets	549
Other assets	123	246
Total assets	34,108	65,229
Current liabilities:
Accounts payable	3,048	2,138
Loan payable, net of discount	3,992
Accrued expenses and other current liabilities	3,370	3,625
Operating lease liabilities	498
Total current liabilities	10,908	5,763
Loan payable, net of current portion and discount	5,988	9,980
Operating lease liabilities, net of current portion	14
Other liabilities		30
Total liabilities	16,910	15,773
Commitments and contingencies (Note 7)
Stockholders’ equity:
Undesignated preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.001 par value; 125,000,000 shares authorized; 24,735,009 and 20,809,025 shares issued and outstanding at December 31, 2019 and 2018, respectively	25	21
Additional paid-in capital	182,117	167,040
Accumulated deficit	(164,944)	(117,605)
Total stockholders’ equity	17,198	49,456
Total liabilities and stockholders’ equity	$ 34,108	$ 65,229

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Undesignated preferred stock, par value	$ 0.001	$ 0.001
Undesignated preferred stock, shares authorized	5,000,000	5,000,000
Undesignated preferred stock, shares issued	0	0
Undesignated preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	24,735,009	20,809,025
Common stock, shares outstanding	24,735,009	20,809,025

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses:
Research and development	$ 37,244	$ 26,376	$ 15,519
General and administrative	9,676	9,217	5,431
Restructuring charges	605
Total operating expenses	47,525	35,593	20,950
Other income (expense):
Interest income (expense), net	270	575	(443)
Other income (expense), net	(84)	(13)	(257)
Loss on extinguishment of debt		(617)
Other income (expense), net	186	(55)	(700)
Net loss	$ (47,339)	$ (35,648)	$ (21,650)
Net loss per share attributable to common stockholders — basic and diluted	$ (2.13)	$ (1.72)	$ (4.80)
Weighted-average common shares outstanding — basic and diluted	22,180,868	20,741,226	4,520,337
Comprehensive loss	$ (47,339)	$ (35,648)	$ (21,650)

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	Series C Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2016		$ 17,967	$ 24,931	$ 52,829
Balance, Shares at Dec. 31, 2016		18,367,344	19,841,270	20,000,000
Balance at Dec. 31, 2016	$ (59,277)				$ 1	$ 1,031	$ (2)	$ (60,307)
Balance, Shares at Dec. 31, 2016					1,341,385
Issuance of common stock, net of issuance costs	66,999				$ 5	66,994
Issuance of common stock, net of issuance costs, shares					5,350,302
Exercise of common stock options	28					28
Exercise of common stock options, shares					33,061
Exercise of common stock warrants, shares					24,401
Accretion of convertible preferred stock to redemption value		$ 7	$ 15	$ 36
Accretion of convertible preferred stock to redemption value	(58)					(58)
Conversion of preferred stock into common stock		$ (17,974)	$ (24,946)	$ (52,865)
Conversion of preferred stock into common stock, shares		(18,367,344)	(19,841,270)	(20,000,000)
Conversion of preferred stock into common stock, shares					13,945,509
Conversion of preferred stock into common stock	95,785				$ 14	95,771
Conversion of warrant liability to equity	524					524
Stock-based compensation	517					517
Change in unrealized gain (loss) on available for sale investments	2						$ 2
Net loss	(21,650)							(21,650)
Balance, Shares at Dec. 31, 2017					20,694,658
Balance at Dec. 31, 2017	82,870				$ 20	164,807		(81,957)
Exercise of common stock options	139				$ 1	138
Exercise of common stock options, shares					106,879
Issuance of common stock through employee stock purchase plan ("ESPP")	34					34
Issuance of common stock through employee stock purchase plan ("ESPP"), shares					7,488
Stock-based compensation	2,049					2,049
Issuance costs related to initial public offering	12					12
Net loss	$ (35,648)							(35,648)
Balance, Shares at Dec. 31, 2018	20,809,025				20,809,025
Balance at Dec. 31, 2018	$ 49,456				$ 21	167,040		(117,605)
Issuance of common stock, net of issuance costs	11,980				$ 4	11,976
Issuance of common stock, net of issuance costs, shares					3,875,848
Exercise of common stock options	36					36
Exercise of common stock options, shares					24,399
Issuance of common stock through employee stock purchase plan ("ESPP")	76					76
Issuance of common stock through employee stock purchase plan ("ESPP"), shares					25,737
Stock-based compensation	2,989					2,989
Net loss	$ (47,339)							(47,339)
Balance, Shares at Dec. 31, 2019	24,735,009				24,735,009
Balance at Dec. 31, 2019	$ 17,198				$ 25	$ 182,117		$ (164,944)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (47,339,000)	$ (35,648,000)	$ (21,650,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	2,989,000	2,049,000	517,000
Depreciation expense	163,000	78,000	73,000
Non-cash interest expense	8,000	161,000	351,000
Non-cash lease expense	486,000
Amortization of premium on investments			33,000
Loss on extinguishment of debt		617,000
Change in fair value of warrant liability			257,000
Changes in assets and liabilities:
Prepaid expenses and other current assets	(202,000)	(1,287,000)	(984,000)
Other assets	123,000	(34,000)	(89,000)
Accounts payable	972,000	441,000	199,000
Accrued expenses	(301,000)	1,764,000	228,000
Operating lease liabilities	(531,000)
Other liabilities		20,000
Net cash used in operating activities	(43,632,000)	(31,839,000)	(21,065,000)
Cash flows from investing activities:
Purchases of property and equipment	(122,000)	(318,000)	(57,000)
Purchases of investments			(1,247,000)
Maturities of investments			24,721,000
Net cash (used in) provided by investing activities	(122,000)	(318,000)	23,417,000
Cash flows from financing activities:
Proceeds from (payments of issuance costs) the issuance of common stock, net of issuance costs	12,035,000	(309,000)	67,197,000
Proceeds from exercise of stock options	36,000	139,000	28,000
Proceeds from issuance of stock through ESPP	76,000	34,000
Proceeds from loan payable		10,000,000
Repayment of loan payable		(10,492,000)	(333,000)
Debt issuance costs paid		(33,000)
Other	(29,000)	(33,000)
Net cash provided by (used in) financing activities	12,118,000	(694,000)	66,892,000
Net (decrease) increase in cash and cash equivalents	(31,636,000)	(32,851,000)	69,244,000
Cash and cash equivalents, beginning of period	61,643,000	94,494,000	25,250,000
Cash and cash equivalents, end of period	30,007,000	61,643,000	94,494,000
Supplemental disclosures:
Cash paid for interest	543,000	906,000	452,000
Property and equipment purchases included in accounts payable		$ 72,000	11,000
Right-of-use assets obtained in exchange of operating lease obligations	992,000
Issuance costs included in accounts payable and accrued expenses	$ 45,000		199,000
Accretion of convertible preferred stock to redemption value			$ 58,000

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Allena Pharmaceuticals, Inc. (the “Company”) is a clinical stage company focused on developing non-absorbed oral enzyme therapeutics to treat metabolic conditions including hyperoxaluria and hyperuricemia. The Company was incorporated under the laws of the State of Delaware on June 24, 2011. The Company’s headquarters are in Newton, Massachusetts. The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any drug product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations, reliance on third party manufacturers, ability to transition from pilot-scale manufacturing to large-scale production of products and the need to obtain adequate additional financing to fund the development of its product candidates. Liquidity and Going Concern The Company had an accumulated deficit of $164.9 million at December 31, 2019, and will require substantial additional capital to fund operations. The future success of the Company is dependent on its ability to identify and develop its product candidates and ultimately upon its ability to attain profitable operations. At December 31, 2019, the Company had $30.0 million of cash and cash equivalents. The Company’s available cash and cash equivalents as of December 31, 2019 are not sufficient to fund the Company’s current operating plan for at least the next twelve months following the filing of this Annual Report. Management expects to seek additional funds through equity or debt financings or through collaborations, licensing transactions or other sources. The Company may be unable to obtain equity or debt financings or enter into collaboration or licensing transactions. The Company may implement cost reduction strategies, which may include amending, delaying, limiting, reducing, or terminating one or more of its ongoing or planned clinical trials of its product candidates. These factors raise substantial doubt about the Company’s ability to continue as a going concern. The accompanying consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty. Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standard Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”).

Summary of Significant Accounti

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 Principles of Consolidation The consolidated financial statements include the accounts of Allena Pharmaceuticals, Inc. and its wholly owned subsidiaries Allena Pharmaceuticals Security Corporation (“Security Corporation”), which was incorporated in December 2014, and Allena Pharmaceuticals Ireland Limited, which was incorporated in March 2017. All intercompany transactions and balances have been eliminated. Use of Estimates The preparation of the Company's consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, expenses and related disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting period. On an ongoing basis, the Company's management evaluates its estimates, which include but are not limited to management’s judgments of prepaid and accrued research and development expenses, and the valuation of share-based awards. Actual results could differ from those estimates. Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision-maker in deciding how to allocate resources and assess performance. The Company's chief operating decision-maker, the Company's chief executive officer, views the Company's operations and manages its business as a single operating segment, which is the business of discovering and developing non-absorbed oral enzyme therapeutics. Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss equaled net loss for the years ended December 31, 2019, 2018 and 2017. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in money market funds. Cash equivalents are stated at cost, which approximates fair value. Cash and cash equivalents consist of the following at December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Cash and cash equivalents: Cash $ 415 $ 228 Money market funds 29,592 61,415 $ 30,007 $ 61,643 Investments The Company classifies its investments in debt securities as available-for-sale. Available-for-sale investments are carried at fair value with unrealized gains and losses included in stockholders’ (deficit) equity. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in interest income (expense) within the statement of operations and comprehensive loss. The Company did not hold any investments at December 31, 2019 and 2018. The Company evaluates its available-for-sale investments with unrealized losses for other-than-temporary impairment. When assessing investments for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary”, the Company reduces the investment to fair value through a charge to the statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented. Concentration of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. The Company maintains all of its cash and cash equivalents at a single accredited financial institution, in amounts that exceed federally insured limits. The Company generally invests its excess cash in money market funds that are subject to minimal credit and market risk. Management has established guidelines relative to credit ratings and maturities intended to safeguard principal balances and maintain liquidity. The investment portfolio is maintained in accordance with the Company’s investment policy, which defines allowable investments, specifies credit quality standards and limits the credit exposure of any single issuer. The Company has no significant off-balance sheet risk such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. Significant Suppliers The Company is dependent on third-party manufacturers to supply products for research and development activities of its programs, including preclinical and clinical testing. 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. Fair Value of Financial Instruments Fair value is defined as the price that would be received upon sale of an asset or paid to transfer a liability between market participants at measurement dates. ASC Topic 820, Fair Value Measurement Level 1 inputs: Quoted prices in active markets for identical assets or liabilities. Level 2 inputs: Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves. Level 3 inputs: Unobservable inputs developed using estimates or assumptions developed by the Company, which reflect those that a market participant would use in pricing the asset or liability. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument's level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Property and Equipment Property and equipment consists of laboratory equipment, computer equipment, software and leasehold improvements recorded at cost. These amounts are depreciated using the straight-line method over the estimated useful lives of the assets as follows: Laboratory equipment 4 years Computer equipment 3 years Software 5 years Leasehold improvements Shorter of useful life or remaining term of related lease Upon retirement or sale, the cost of the assets disposed of and the related accumulated depreciation are eliminated from the balance sheet and related gains or losses are reflected in the statement of operations and comprehensive loss. Repairs and maintenance costs are expensed as incurred and costs of significant improvements are capitalized. Impairment of Long-Lived Assets The Company continually evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company did not recognize any impairment losses for the years ended December 31, 2019, 2018 and 2017. Leases The Company determines at the inception of an arrangement whether the arrangement contains a lease. If a lease is identified in an arrangement, the Company recognizes a right-of-use asset and liability on its balance sheet and determines whether the lease should be classified as a finance or operating lease. The Company does not recognize assets or liabilities for leases with lease terms of less than 12 months. A lease qualifies as a finance lease if any of the following criteria are met at the inception of the lease: (i) there is a transfer of ownership of the leased asset to the Company by the end of the lease term, (ii) the Company holds an option to purchase the leased asset that it is reasonably certain to exercise, (iii) the lease term is for a major part of the remaining economic life of the leased asset, (iv) the present value of the sum of lease payments equals or exceeds substantially all of the fair value of the leased asset, (v) the nature of the leased asset is specialized to the point that it is expected to provide the lessor no alternative use at the end of the lease term. All other leases are recorded as operating leases. Finance and operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease. If the rate implicit is not readily determinable, the Company’s utilizes its incremental borrowing rate at the lease commencement date. Operating lease assets are further adjusted for prepaid or accrued lease payments. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. Finance lease assets are amortized to depreciation expense using the straight-line method over the shorter of the useful life of the related asset or the lease term. Finance lease payments are bifurcated into (i) a portion that is recorded as imputed interest expense and (ii) a portion that reduces the finance liability associated with the lease. The Company separates lease and non-lease components when determining which lease payments to include in the calculation of its lease assets and liabilities. Variable lease payments are expensed as incurred. If a lease includes an option to extend or terminate the lease, the Company reflects the option in the lease term if it is reasonably certain it will exercise the option. Operating leases are recorded in “Operating lease assets,” “Operating lease liabilities” and “Operating lease liabilities, net of current portion” on the Company’s consolidated balance sheet. The Company did not have any finance leases recorded on its consolidated balance sheet as of December 31, 2019. Research and Development The Company expenses all costs incurred in performing research and development activities. Research and development expenses include salaries and benefits, materials and supplies, preclinical and clinical trial expenses, manufacturing expenses, stock-based compensation expense, depreciation of equipment, contract services and other outside expenses. Costs of certain development activities, such as manufacturing, are recognized based on an evaluation of the progress to completion of specific tasks. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid or accrued research and development costs. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed. Patent Costs The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the accompanying consolidated statements of operations and comprehensive loss. Accounting for Stock-Based Compensation The Company accounts for its stock-based compensation in accordance with ASC Topic 718, Compensation—Stock Compensation Equity-Based Payments to Non-Employees The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Due to the lack of a public market for the Company’s common stock and a lack of company-specific historical and implied volatility data, the Company has based its computation of expected volatility on the historical volatility of a representative group of public companies with similar characteristics to the Company, including stage of product development and life science industry focus. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment The Company expenses the fair value of its share-based compensation awards on a straight-line basis over the requisite service period, which is generally the vesting period. Income Taxes The Company accounts for income taxes using the liability method in accordance with ASC Topic 740, Income Taxes The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. Net Loss Per Share The Company has reported losses since inception and has computed basic net loss per share attributable to common stockholders by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. The Company has computed diluted net loss per common share after giving consideration to all potentially dilutive common shares, including options to purchase common stock, restricted common stock, convertible preferred stock and warrants to purchase convertible preferred stock, outstanding during the period determined using the treasury-stock and if-converted methods, except where the effect of including such securities would be anti-dilutive. Because the Company has reported net losses since inception, these potential common shares have been anti-dilutive and basic and diluted loss per share have been the same. Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share data): Years Ended December 31, 2019 2018 2017 Numerator: Net loss $ (47,339 ) $ (35,648 ) $ (21,650 ) Accretion of convertible preferred stock — — (58 ) Net loss attributable to common stockholders $ (47,339 ) $ (35,648 ) $ (21,708 ) Denominator: Weighted-average common shares – basic and diluted 22,180,868 20,741,226 4,520,337 Net loss per share attributable to common stockholders –basic and diluted $ (2.13 ) $ (1.72 ) $ (4.80 ) The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share because to include them would be anti-dilutive (in common stock equivalent shares): Years Ended December 31, 2019 2018 2017 Warrants 9,040 9,040 9,040 Stock options 3,915,591 2,141,527 1,508,124 Restricted stock units 517,750 — — Total 4,442,381 2,150,567 1,517,164 Loss Contingencies In accordance with ASC 450, Contingencies Guarantees The Company has identified the guarantees described below as disclosable, in accordance with ASC 460, Guarantees As permitted under Delaware law, the Company indemnifies its officers and directors for certain events or occurrences while the officer or director is, or was, serving at the Company’s request in such capacity. The maximum potential amount of future payments the Company could be required to make is unlimited; however, the Company has directors’ and officers’ insurance coverage that should limit its exposure and enable it to recover a portion of any future amounts paid. The Company is a party to a number of agreements entered into in the ordinary course of business that contain typical provisions that obligate the Company to indemnify the other parties to such agreements upon the occurrence of certain events. Such indemnification obligations are usually in effect from the date of execution of the applicable agreement for a period equal to the applicable statute of limitations. The aggregate maximum potential future liability of the Company under such indemnification provisions is uncertain. The Company leases office space under several noncancelable operating leases. The Company has standard indemnification arrangements under these leases that require it to indemnify the landlord against all costs, expenses, fines, suits, claims, demands, liabilities, and actions directly resulting from any breach, violation, or nonperformance of any covenant or condition of the respective lease. As of December 31, 2019 and 2018, the Company had not experienced any losses related to these indemnification obligations, and no material claims with respect thereto were outstanding. The Company does not expect significant claims related to these indemnification obligations and, consequently, concluded that the fair value of these obligations is negligible, and no related reserves have been established. Recently Adopted Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its consolidated financial position or results of operations upon adoption. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) Leases (Topic 842): Targeted Improvements In June 2018, the FASB issued ASU No. 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting Recently Issued Accounting Pronouncements In 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract In 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement In 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In December 2019, the FASB issued ASU No. 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes,” which is intended to simplify various aspects related to accounting for income taxes. The pronouncement is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2020, with early adoption permitted. ASU No. 2019-12 is effective for us beginning in fiscal 2021. The Company is currently in the process of evaluating the effects of this pronouncement on our financial statements.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The following tables present information about the Company’s financial assets and liabilities that have been measured at fair value at December 31, 2019 and 2018 and indicates the fair value hierarchy of the valuation inputs utilized to determine such fair value (in thousands): Description December 31, 2019 Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds, included in cash and cash equivalents $ 29,592 $ 29,592 $ — $ — Total assets $ 29,592 $ 29,592 $ — $ — Description December 31, 2018 Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds, included in cash and cash equivalents $ 61,415 $ 61,415 $ — $ — Total assets $ 61,415 $ 61,415 $ — $ — At December 31, 2019 and 2018, all of the Company’s cash equivalents were comprised of money market funds. There have been no changes to the valuation methods used during the years ended December 31, 2019 and 2018. There were no transfers within the fair value hierarchy during the years ended December 31, 2019 and 2018. The carrying amounts reflected in the consolidated balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their carrying values. The Company believes the terms of the loan payable reflect current market conditions for an instrument with similar terms and maturity, therefore the carrying value of the Company’s debt approximates its fair value based on Level 3 of the fair value hierarchy. Warrants to Purchase Shares Subject to Redemption Prior to the Company’s IPO, the Company had warrants outstanding for the purchase of shares of convertible preferred stock (the “Warrants”) that were measured at fair value at each reporting period through the date of the Company’s IPO using then-current assumptions with changes in fair value charged to other income (expense) on the statements of operations and comprehensive loss. The following table sets forth a summary of changes in the fair value of the Warrants, which represented a recurring measurement classified within Level 3 of the fair value hierarchy, wherein fair value was estimated using significant unobservable inputs (in thousands, except share data): Balance at December 31, 2016 $ 267 Change in fair value of Warrants through the date of the IPO included in other income (expense) 257 Fair value of Warrants reclassified to stockholders' equity (deficit) upon conversion to warrants for the conversion of common stock (524 ) Balance at December 31, 2017 $ — An entity may choose to measure many financial instruments and certain other items at fair value at specified election dates. Subsequent unrealized gains and losses on items for which the fair value option has been elected will be reported in earnings. The Company did not elect to measure any financial instruments or other items at fair value.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Property and Equipment, Net	4. Property and Equipment, Net Property and equipment includes the following at December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Property and equipment: Laboratory equipment $ 779 $ 728 Computer equipment 6 6 Software 39 39 824 773 Less: Accumulated depreciation (423 ) (259 ) Property and equipment, net $ 401 $ 514 The Company recognized $163,000, $78,000 and $73,000 of depreciation expense for the years ended December 31, 2019, 2018 and 2017, respectively.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses consist of the following (in thousands): December 31, 2019 2018 Payroll and employee-related expenses $ 1,250 $ 1,690 Third-party research and development expenses 1,393 1,514 Professional fees 229 299 Restructuring charges 373 — Loan interest 43 46 Other 82 76 Total accrued expenses $ 3,370 $ 3,625

Restructuring Charges

Restructuring Charges	12 Months Ended
	Dec. 31, 2019
Restructuring And Related Activities [Abstract]
Restructuring Charges	6. Restructuring Charges On November 29, 2019, following the completion of a strategic review of its business, the Company's Board of Directors approved a workforce reduction plan, or the Workforce Reduction, to reduce its workforce headcount by approximately 38%. The Company evaluated the related employee severance and other benefits to employees in connection with the Workforce Reduction to determine whether the benefits were within the scope ASC 712, Compensation - Non-retirement Post-employment Benefits Exit or Disposal Cost Obligations, The following table outlines the components of the restructuring charges during the year ended December 31, 2019 included in the consolidated statement of operations, and ending liability recorded in the balance sheet as at December 31, 2019 (in thousands): Charges incurred during the year ended December 31, 2019 Amount paid through December 31, 2019 Remaining liability at December 31, 2019 Employee severance, bonus and other $ 605 $ (232 ) $ 373 Total restructuring charges $ 605 $ (232 ) $ 373

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies The Company is a party to operating leases for approximately 7,795 square feet of office space in Newton, MA (Newton Lease), and for approximately 7,564 square feet of laboratory and office space in Sudbury, MA (Sudbury Lease). The Newton Lease expires on December 31, 2020 and the Sudbury Lease expires on February 28, 2021. Annualized base rent for the Newton Lease and the Sudbury lease is approximately $0.3 million and $0.2 million, respectively. Aggregate Lease Information Related to the Application of ASC 842 Maturities of the Company’s operating lease liabilities in accordance with ASC 842 as of December 31, 2019 are as follows (in thousands): 2020 $ 498 2021 30 Total maturities $ 528 Less: Amount representing interest (16 ) Present value of operating lease liabilities $ 512 Lease costs included in the Company’s consolidated statements of operations and comprehensive loss for the year ended December 31, 2019 were $0.5 million. The Company’s operating leases had a weighted average remaining lease term of 1.0 years and a weighted average discount rate of 5.5% at December 31, 2019. Additional Lease Information Related to the Application of ASC 840 The following information is disclosed in accordance with ASC 840, Leases (Topic 840) 2019 $ 487 2020 539 2021 30 $ 1,056 During the years ended December 31, 2018 and 2017, rent expense was $0.5 million and $0.4 million, respectively. License Agreement In March 2012, the Company entered into an exclusive license agreement (“License Agreement”) with Althea Technologies, Inc. (“Althea”) for certain intellectual property. The Company reimbursed Althea for patent related fees and costs incurred by Althea totaling $0.1 million in the aggregate and issued a total of 88,186 shares of common stock to Althea. Under the terms of the License Agreement, the Company agreed to pay annual license maintenance fees, milestone payments and royalties as a percentage of net sales. Annual license maintenance fees are creditable against royalties earned during the same calendar year and are not material to the financial statements. Milestone payments are triggered upon the achievement of specified development, regulatory and commercialization milestones and are not creditable against royalties. Actual amounts due under the License Agreement will vary depending on the number of products developed, the type and development path of the products, and other related factors. Milestone payments could total up to $

Loan and Security Agreement

Loan and Security Agreement	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Loan and Security Agreement	8. Loan and Security Agreement At December 31, 2017, the Company had $9.7 million outstanding under a loan agreement with SVB, as amended (“Amended SVB Loan Agreement”). The Company was also required to make a final payment equal to 8.25% of the total borrowings (“Final Payment”) on the earliest of the loan maturity date, an acceleration of the loan as defined in the Amended SVB Loan Agreement or at the time of prepayment. On June 29, 2018, the Company terminated the Amended SVB Loan Agreement and repaid the $7.7 million outstanding principal balance and the Final Payment to SVB. The Company recorded a loss on extinguishment of debt of $0.6 million in the Statement of Operations, accordingly. On June 29, 2018 the Company also entered into a loan agreement with Pacific Western Bank (“PWB Loan Agreement”) providing up to $12.0 million of borrowings, of which $10.0 million was advanced on June 29, 2018. The remaining $2.0 million of borrowings available under the PWB Loan Agreement were available to the Company through one additional advance request until December 31, 2019, the end of the interest only period as defined below. The Company did not request an additional advance prior to the end of the interest only period. Borrowings are secured by a lien on all Company assets, excluding intellectual property, and amounts borrowed have a floating per annum interest rate of the greater of 5.0% or the prime rate. The PWB Loan Agreement has a term of 48 months and an interest only period of 18 months. Upon the expiration of the interest only period on December 31, 2019, amounts borrowed will be repaid over 30 equal monthly payments of principal plus accrued but unpaid interest. At its option, the Company may prepay all, but not less than all, of the outstanding borrowings subject to a prepayment premium as defined in the Loan Agreement. Upon the closing of one or more financings, in which the Company receives aggregate gross proceeds of at least $25 million, a success fee of $300,000 will be due and payable to PWB. The Company’s obligation to pay this Success Fee survives termination of the Agreement. The PWB Loan Agreement contains negative covenants restricting the Company’s activities, including limitations on dispositions, mergers or acquisitions, incurring indebtedness or liens, paying dividends or making investments and certain other business transactions. There are no financial covenants associated with the PWB Loan Agreement. The obligations under the PWB Loan Agreement are subject to acceleration upon the occurrence of specified events of default, including a material adverse change in the Company’s business, operations or financial or other condition. The Company has determined that the risk of subjective acceleration under the material adverse events clause is remote and therefore has classified the outstanding principal based on scheduled principal payments. The Company evaluated the PWB Loan Agreement for embedded features that require bifurcation, noting certain features were required to be bifurcated, but were concluded to be de minimis in value at December 31, 2019. The minimum aggregate future loan and interest payments at December 31, 2019 are as follows (in thousands): Years Ending December 31, 2020 4,409 2021 4,208 2022 2,029 Total minimum payments 10,646 Less: Amount representing interest (645 ) Less: Discount (21 ) Less: Current portion (3,992 ) Loan payable, net of current portion $ 5,988

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Stockholders' Equity	9. Stockholders’ Equity On November 6, 2017, the Company completed an initial public offering (“IPO”), in which the Company issued and sold 5,333,333 shares of its common stock at a public offering price of $14.00 per share, for aggregate gross proceeds of $74.7 million. The underwriters partially exercised their over-allotment option on December 1, 2017, and purchased an additional 16,969 shares of our common stock for aggregate gross proceeds of $0.2 million. As a result of the IPO, the Company received approximately $67.0 million in net proceeds after deducting $7.9 million of underwriting discounts and commissions and offering costs. Upon the closing of the IPO, all of the outstanding shares of convertible preferred stock automatically converted into 13,945,509 shares of common stock. On June 28, 2019, the Company completed a registered direct offering in which the Company issued and sold 2,632,092 shares of its common stock, at a purchase price of $3.80 per share, for gross proceeds of $10.0 million through a securities purchase agreement with the investors. As a result of the registered direct offering, the Company received approximately $9.4 million in net proceeds after deducting offering costs. In December 2018, the Company entered into an At-the-Market Equity Offering Sales Agreement (“ATM Agreement”), with Cowen and Company, LLC (“Cowen”), under which the Company was authorized to issue and sell shares of its common stock having aggregate sales proceeds of up to $50 million from time to time through Cowen, acting as sales agent and/or principal. The Company agreed to pay Cowen a commission of 3.0% of the gross proceeds from any sales of shares of its common stock under this facility. On December 30, 2019, the Company completed an issuance and sale of approximately 1.2 million shares of common stock under the ATM Agreement. As a result of this issuance and sale of common stock, the Company received approximately $2.6 million in net proceeds after deducting offering costs. Common Stock The holders of common stock are entitled to one vote for each share held. Common stockholders are not entitled to receive dividends, unless declared by the Board of Directors. The Company has reserved for future issuances the following shares of common stock as of December 31, 2019 and 2018: December 31, 2019 December 31, 2018 Warrants 9,040 9,040 Stock options and restricted stock units 5,070,303 4,262,341 Employee stock purchase plan 380,005 405,742 Total 5,459,348 4,677,123 Warrants At December 31, 2019 and 2018, the Company has 9,040 warrants outstanding for the purchase of shares of common stock at an exercise price of $11.06. The warrants expire on May 1, 2026.

Stock Incentive Plans

Stock Incentive Plans	12 Months Ended
	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Incentive Plans	10. Stock Incentive Plans Stock Option Plans The Company adopted the 2017 Stock Option and Incentive Plan (“2017 Plan”) on October 31, 2017. Upon adoption of the 2017 Plan, no further grants were made under the 2011 Stock Incentive Plan (“2011 Plan”). The 2017 Plan initially provided for the grant of awards for 2,038,021 shares of common stock. In addition to the shares available for grant under the 2017 Plan, any awards outstanding under the 2011 Plan as of the October 31, 2017 that are cancelled, forfeited or otherwise terminated without being exercised, the number of shares underlying such awards are available for future grant under the 2017 Plan. The 2017 Plan also provides that an additional number of shares will automatically be added to the shares authorized for issuance under the 2017 Plan on January 1 of each year. The number of shares added each year will be equal to the lesser of: (i) 4% of the outstanding shares on the immediately preceding December 31 or (ii) such amount as determined by the Compensation Committee of the registrant’s Board of Directors. On January 1, 2018, 2019 and 2020, the shares available for grant under the 2017 Plan was automatically increased by 827,786, 832,361 and 989,400 shares, respectively. All of the Company’s employees, officers, directors, consultants and advisors are eligible to be granted options, restricted stock units (“RSUs”), and other share-based awards under the terms of the 2017 Plan. As of December 31, 2019, 636,962 shares of common stock were available for future grant under the 2017 Plan. All stock option grants are nonstatutory stock options except option grants to employees (including officers and directors) intended to qualify as incentive stock options under the Internal Revenue Code of 1986, as amended. Incentive stock options may not be granted at less than the fair market value of the Company’s common stock on the date of grant. Nonqualified stock options may be granted at an exercise price established by the Board of Directors at its sole discretion (which has not been less than fair market value on the date of grant) and the vesting periods may vary. Vesting periods are generally four years and are determined by the Board of Directors or a delegated subcommittee. Stock options become exercisable as they vest. Stock options granted under the 2017 and 2011 Plans expire no more than 10 years from the date of grant. Stock-based compensation expense included in the Company’s statements of operations and comprehensive loss is as follows (in thousands): Years Ended December 31, 2019 2018 2017 Research and development $ 1,175 $ 584 $ 147 General and administrative 1,814 1,465 370 Total $ 2,989 $ 2,049 $ 517 The fair value of each stock option granted to employees and directors was estimated on the date of grant using the Black-Scholes option-pricing model, with the following range of assumptions for the years ended December 31, 2019, 2018 and 2017: Years Ended December 31, 2019 2018 2017 Risk-free interest rate 1.4% – 2.6% 2.3% – 3.1% 1.9% – 2.3% Expected dividend yield —% —% —% Expected term (in years) 5.5 – 6.8 5.5 – 6.1 5.6 – 6.3 Expected volatility 80% 81% 81% The expense related to awards granted to employees and directors for their service on the Board of Directors was $2.9 million, $1.9 million, and $0.5 million for the years ended December 31, 2019, 2018 and 2017, respectively. The Company did not grant any stock options to non-employees during the years ended December 31, 2019 or 2018. The expense related to awards granted to non-employees was not material to the consolidated financial statements for the years ended December 31, 2019, 2018 and 2017. A summary of the stock option activity under the 2017 and 2011 Plans is as follows: Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2018 2,141,527 $ 4.32 7.7 $ 4,959 Granted 2,021,550 4.65 Exercised (24,399 ) 1.49 Cancelled (223,087 ) 7.35 Outstanding at December 31, 2019 3,915,591 $ 4.33 8.1 $ 1,921 Exercisable at December 31, 2019 1,686,341 $ 3.43 6.5 $ 1,589 The weighted-average fair value of options granted to employees and directors for their service on the Board of Directors during the years ended December 31, 2019, 2018 and 2017 was $3.29, $6.21 and $6.16 per share, respectively. The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The total intrinsic value of options exercised during the years ended December 31, 2019, 2018 and 2017 was $58,000, $1.2 million and $276,000, respectively. As of December 31, 2019, total unrecognized stock-based compensation expense relating to unvested stock options was $7.1 million. This amount is expected to be recognized over a weighted-average period of 2.8 years. Restricted Stock Units (RSUs) The Company has also made awards of time-based RSUs to certain employees and officers of the Company. On December 2, 2019, the Company awarded 517,750 RSUs to employees and officers of the Company. The RSUs vest as to 50% on June 2, 2020 and 50% on December 2, 2020. The RSUs are generally forfeited if the employment relationship terminates with the Company prior to vesting. For the year ended December 31, 2019, the Company recognized approximately $0.1 million of stock-based compensation expense related to these awards. As of December 31, 2019, the total remaining unrecognized compensation cost related to all nonvested RSUs amounted to $1.2 million, which is expected to be recognized during 2020. Shares Weighted-Average Grant Date Fair Value Nonvested at January 1, 2019 — $ — Granted 517,750 2.42 Vested — — Forfeited — — Nonvested at December 31, 2019 517,750 $ 2.42 Employee Stock Purchase Plan The Company adopted the 2017 Employee Stock Purchase Plan (“ESPP”) on October 31, 2017. The ESPP permits eligible employees to enroll in six-month offering periods. Participants may purchase shares of the Company’s common stock, through payroll deductions, at a price equal to 85% of the fair market value of the common stock on the first or last day of the applicable six-month offering period, whichever is lower. Purchase dates under the ESPP occur on or about January 1 and July 1 each year. The ESPP initially reserved 206,284 shares of common stock for issuance. The ESPP also provides that an additional number of shares will automatically be added to the shares authorized for issuance under the ESPP on January 1 of each year. The number of shares added each year will be equal to the lesser of: (i) 1% of the outstanding shares on the immediately preceding December 31 or (ii) such amount as determined by the Compensation Committee of the registrant’s Board of Directors. On January 1, 2018 the shares available for grant under the ESPP was automatically increased by 206,946 shares. No shares were added to the ESPP on January 1, 2019 and 2020. During the years ended December 31, 2019 and 2018, $76,000 and $35,000, respectively, was withheld from employees, on an after-tax basis, in order to purchase 25,737 and 7,488 shares of the Company’s common stock, respectively. As of December 31, 2019, 380,005 shares of Company’s common stock remained available for issuance under the ESPP.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes Income Taxes The Company records a provision or benefit for income taxes on pre-tax income or loss based on its estimated effective tax rate for the year. During the years ended December 31, 2019, 2018 and 2017, the Company recorded net losses of approximately $47.3 million, $35.6 million and $21.7 million, respectively and, since it maintains a full valuation allowance on its deferred tax assets, the Company did not record an income tax benefit for the years ended December 31, 2019, 2018 or 2017. Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets are comprised of the following (in thousands): December 31, 2019 2018 Deferred tax assets: Net operating loss carryforwards $ 42,549 $ 30,294 Research and development credits 8,138 5,843 Licenses 19 21 Stock based compensation 811 369 Operating lease liabilities 140 — Other 281 418 Total gross deferred tax assets 51,938 36,945 Less: Valuation allowance (51,800 ) (36,945 ) Net deferred tax assets 138 — Deferred tax liabilities: Operating lease assets (138 ) — Total gross deferred tax liabilities (138 ) — Net deferred taxes $ — $ — ASC 740 requires a valuation allowance to reduce the deferred tax assets reported if, based on the weight of the evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. After consideration of all the evidence, both positive and negative, the Company has recorded a valuation allowance against its deferred tax assets at December 31, 2019 and 2018, respectively, because the Company's management has determined that it is more likely than not that the Company will not recognize the benefits of its federal and state deferred tax assets primarily due to its cumulative loss position and, as a result, a valuation allowance of $51.8 million and $36.9 million has been established at December 31, 2019 and 2018, respectively. The valuation allowance increased by approximately $14.9 million and $10.6 million for the years ended December 31, 2019 and 2018, respectively, due primarily to the generation of net operating losses. A reconciliation of income tax expense computed at the statutory federal income tax rate to income taxes reflected in the financial statements is as follows: 2019 2018 2017 Income tax computed at federal statutory tax rate 21.0 % 21.0 % 34.0 % Permanent differences — % — % (1.9 )% State taxes, net of federal benefit 6.1 % 6.2 % 4.8 % Research and development and other tax credits 4.9 % 3.1 % 5.0 % Stock based compensation (0.6 )% (0.5 )% (0.5 )% Federal rate change — % — % (42.7 )% Change in deferred tax asset valuation allowance (31.4 )% (29.8 )% 1.3 % — % — % — % As of December 31, 2019 and 2018, the Company had U.S. federal net operating loss carryforwards of approximately $155.9 million and $111.1 million, respectively, which may be available to offset future income tax liabilities. Of the $155.9 million net operating loss carryforward as of December 31, 2019, $78.0 million has an indefinite life and $77.9 million will expire at various dates through 2037. As of December 31, 2019 and 2018, the Company also had U.S. state net operating loss carryforwards of approximately $155.0 million and $110.3 million, respectively, which may be available to offset future income tax liabilities and expire at various dates through 2039. As of December 31, 2019 and 2018, the Company had federal research and development tax credit carryforwards of approximately $5.9 million and $4.0 million, respectively, available to reduce future tax liabilities which expire at various dates through 2039. As of December 31, 2019 and 2018, the Company had state research and development tax credit carryforwards of approximately $2.8 million and $2.2 million, respectively, available to reduce future tax liabilities which expire at various dates through 2034. The Company has generated research credits but has not conducted a study to document the qualified activity. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance. Under the provisions of the Internal Revenue Code, the net operating loss and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. Net operating loss and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has completed several financings since its inception which resulted in a change in control as defined by Sections 382 and 383 of the Internal Revenue Code. Ownership changes, as defined in the Internal Revenue Code, including those resulting from the issuance of common stock in connection with our public offerings, may limit the amount of net operating loss and tax credit carryforwards that can be utilized to offset future taxable income or tax liability. The amount of the limitation is determined in accordance with Section 382 of the Internal Revenue Code. We have performed an analysis of ownership changes through December 31, 2019. Based on this analysis, we do not believe that any of our tax attributes will expire unutilized due to Section 382 limitations. The Company will recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2019 and 2018, the Company had no accrued interest or penalties related to uncertain tax positions and no such amounts have been recognized in the Company’s statements of operations and comprehensive loss. The Company files income tax returns in the United States and various state jurisdictions. The federal, state and foreign income tax returns are generally subject to tax examinations for the tax years ended December 31, 2016 through December 31, 2019. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service, state tax authorities to the extent utilized in a future period.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2019
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Employee Benefit Plan	12. Employee Benefit Plan Effective January 2012, employees of the Company are eligible to participate in the Company’s 401(k) retirement plan (“401(k) Plan”). Participants may contribute up to 100% of their annual compensation to the 401(k) Plan, subject to statutory limitations. Through December 31, 2018, the 401(k) Plan did not allow the Company to make matching contributions. Effective January 1, 2019, the Company amended the 401(k) Plan to allow the Company to make matching contributions. The 401(k) Plan matches 100% of employee contributions up to a maximum of 4% of employees’ salary. Matching contributions are fully vested at the time of contribution. During the year ended December 31, 2019, matching contribution costs incurred by the Company were $0.3 million.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	13. Selected Quarterly Financial Data (Unaudited) The following table contains quarterly financial information for 2019 and 2018. The Company believes that the following information reflects all normal recurring adjustments necessary for the fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. 2019 First Quarter Second Quarter Third Quarter Fourth Quarter Total (in thousands, except per share amounts) Total operating expenses $ 11,559 $ 11,335 $ 13,338 $ 11,293 $ 47,525 Loss from operations (11,559 ) (11,335 ) (13,338 ) (11,293 ) (47,525 ) Net loss (11,419 ) (11,273 ) (13,288 ) (11,359 ) (47,339 ) Net loss attributable to common stockholders - basic and diluted $ (0.55 ) $ (0.54 ) $ (0.57 ) $ (0.47 ) $ (2.13 ) 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Total (in thousands, except per share amounts) Total operating expenses $ 7,973 $ 8,135 $ 9,705 $ 9,780 $ 35,593 Loss from operations (7,973 ) (8,135 ) (9,705 ) (9,780 ) (35,593 ) Net loss (7,880 ) (8,647 ) (9,510 ) (9,611 ) (35,648 ) Net loss attributable to common stockholders - basic and diluted $ (0.38 ) $ (0.42 ) $ (0.46 ) $ (0.46 ) $ (1.72 )

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standard Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”).
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of Allena Pharmaceuticals, Inc. and its wholly owned subsidiaries Allena Pharmaceuticals Security Corporation (“Security Corporation”), which was incorporated in December 2014, and Allena Pharmaceuticals Ireland Limited, which was incorporated in March 2017. All intercompany transactions and balances have been eliminated.
Use of Estimates	Use of Estimates The preparation of the Company's consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, expenses and related disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting period. On an ongoing basis, the Company's management evaluates its estimates, which include but are not limited to management’s judgments of prepaid and accrued research and development expenses, and the valuation of share-based awards. Actual results could differ from those estimates.
Segment Information	Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision-maker in deciding how to allocate resources and assess performance. The Company's chief operating decision-maker, the Company's chief executive officer, views the Company's operations and manages its business as a single operating segment, which is the business of discovering and developing non-absorbed oral enzyme therapeutics.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss equaled net loss for the years ended December 31, 2019, 2018 and 2017.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in money market funds. Cash equivalents are stated at cost, which approximates fair value. Cash and cash equivalents consist of the following at December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Cash and cash equivalents: Cash $ 415 $ 228 Money market funds 29,592 61,415 $ 30,007 $ 61,643
Investments	Investments The Company classifies its investments in debt securities as available-for-sale. Available-for-sale investments are carried at fair value with unrealized gains and losses included in stockholders’ (deficit) equity. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in interest income (expense) within the statement of operations and comprehensive loss. The Company did not hold any investments at December 31, 2019 and 2018. The Company evaluates its available-for-sale investments with unrealized losses for other-than-temporary impairment. When assessing investments for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary”, the Company reduces the investment to fair value through a charge to the statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.
Concentration of Credit Risk and Off-Balance Sheet Risk	Concentration of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. The Company maintains all of its cash and cash equivalents at a single accredited financial institution, in amounts that exceed federally insured limits. The Company generally invests its excess cash in money market funds that are subject to minimal credit and market risk. Management has established guidelines relative to credit ratings and maturities intended to safeguard principal balances and maintain liquidity. The investment portfolio is maintained in accordance with the Company’s investment policy, which defines allowable investments, specifies credit quality standards and limits the credit exposure of any single issuer. The Company has no significant off-balance sheet risk such as foreign exchange contracts, option contracts, or other foreign hedging arrangements.
Significant Suppliers	Significant Suppliers The Company is dependent on third-party manufacturers to supply products for research and development activities of its programs, including preclinical and clinical testing. 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.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value is defined as the price that would be received upon sale of an asset or paid to transfer a liability between market participants at measurement dates. ASC Topic 820, Fair Value Measurement Level 1 inputs: Quoted prices in active markets for identical assets or liabilities. Level 2 inputs: Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves. Level 3 inputs: Unobservable inputs developed using estimates or assumptions developed by the Company, which reflect those that a market participant would use in pricing the asset or liability. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument's level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.
Property and Equipment	Property and Equipment Property and equipment consists of laboratory equipment, computer equipment, software and leasehold improvements recorded at cost. These amounts are depreciated using the straight-line method over the estimated useful lives of the assets as follows: Laboratory equipment 4 years Computer equipment 3 years Software 5 years Leasehold improvements Shorter of useful life or remaining term of related lease Upon retirement or sale, the cost of the assets disposed of and the related accumulated depreciation are eliminated from the balance sheet and related gains or losses are reflected in the statement of operations and comprehensive loss. Repairs and maintenance costs are expensed as incurred and costs of significant improvements are capitalized.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company continually evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company did not recognize any impairment losses for the years ended December 31, 2019, 2018 and 2017.
Leases	Leases The Company determines at the inception of an arrangement whether the arrangement contains a lease. If a lease is identified in an arrangement, the Company recognizes a right-of-use asset and liability on its balance sheet and determines whether the lease should be classified as a finance or operating lease. The Company does not recognize assets or liabilities for leases with lease terms of less than 12 months. A lease qualifies as a finance lease if any of the following criteria are met at the inception of the lease: (i) there is a transfer of ownership of the leased asset to the Company by the end of the lease term, (ii) the Company holds an option to purchase the leased asset that it is reasonably certain to exercise, (iii) the lease term is for a major part of the remaining economic life of the leased asset, (iv) the present value of the sum of lease payments equals or exceeds substantially all of the fair value of the leased asset, (v) the nature of the leased asset is specialized to the point that it is expected to provide the lessor no alternative use at the end of the lease term. All other leases are recorded as operating leases. Finance and operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease. If the rate implicit is not readily determinable, the Company’s utilizes its incremental borrowing rate at the lease commencement date. Operating lease assets are further adjusted for prepaid or accrued lease payments. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. Finance lease assets are amortized to depreciation expense using the straight-line method over the shorter of the useful life of the related asset or the lease term. Finance lease payments are bifurcated into (i) a portion that is recorded as imputed interest expense and (ii) a portion that reduces the finance liability associated with the lease. The Company separates lease and non-lease components when determining which lease payments to include in the calculation of its lease assets and liabilities. Variable lease payments are expensed as incurred. If a lease includes an option to extend or terminate the lease, the Company reflects the option in the lease term if it is reasonably certain it will exercise the option. Operating leases are recorded in “Operating lease assets,” “Operating lease liabilities” and “Operating lease liabilities, net of current portion” on the Company’s consolidated balance sheet. The Company did not have any finance leases recorded on its consolidated balance sheet as of December 31, 2019.
Research and Development	Research and Development The Company expenses all costs incurred in performing research and development activities. Research and development expenses include salaries and benefits, materials and supplies, preclinical and clinical trial expenses, manufacturing expenses, stock-based compensation expense, depreciation of equipment, contract services and other outside expenses. Costs of certain development activities, such as manufacturing, are recognized based on an evaluation of the progress to completion of specific tasks. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid or accrued research and development costs. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed.
Patent Costs	Patent Costs The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the accompanying consolidated statements of operations and comprehensive loss.
Accounting for Stock-Based Compensation	Accounting for Stock-Based Compensation The Company accounts for its stock-based compensation in accordance with ASC Topic 718, Compensation—Stock Compensation Equity-Based Payments to Non-Employees The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Due to the lack of a public market for the Company’s common stock and a lack of company-specific historical and implied volatility data, the Company has based its computation of expected volatility on the historical volatility of a representative group of public companies with similar characteristics to the Company, including stage of product development and life science industry focus. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment The Company expenses the fair value of its share-based compensation awards on a straight-line basis over the requisite service period, which is generally the vesting period.
Income Taxes	Income Taxes The Company accounts for income taxes using the liability method in accordance with ASC Topic 740, Income Taxes The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained. Recognized income tax positions are measured at the largest amount that is greater than 50% likely of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs.
Net Loss Per Share	Net Loss Per Share The Company has reported losses since inception and has computed basic net loss per share attributable to common stockholders by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. The Company has computed diluted net loss per common share after giving consideration to all potentially dilutive common shares, including options to purchase common stock, restricted common stock, convertible preferred stock and warrants to purchase convertible preferred stock, outstanding during the period determined using the treasury-stock and if-converted methods, except where the effect of including such securities would be anti-dilutive. Because the Company has reported net losses since inception, these potential common shares have been anti-dilutive and basic and diluted loss per share have been the same. Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share data): Years Ended December 31, 2019 2018 2017 Numerator: Net loss $ (47,339 ) $ (35,648 ) $ (21,650 ) Accretion of convertible preferred stock — — (58 ) Net loss attributable to common stockholders $ (47,339 ) $ (35,648 ) $ (21,708 ) Denominator: Weighted-average common shares – basic and diluted 22,180,868 20,741,226 4,520,337 Net loss per share attributable to common stockholders –basic and diluted $ (2.13 ) $ (1.72 ) $ (4.80 ) The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share because to include them would be anti-dilutive (in common stock equivalent shares): Years Ended December 31, 2019 2018 2017 Warrants 9,040 9,040 9,040 Stock options 3,915,591 2,141,527 1,508,124 Restricted stock units 517,750 — — Total 4,442,381 2,150,567 1,517,164
Loss Contingencies	Loss Contingencies In accordance with ASC 450, Contingencies
Guarantees	Guarantees The Company has identified the guarantees described below as disclosable, in accordance with ASC 460, Guarantees As permitted under Delaware law, the Company indemnifies its officers and directors for certain events or occurrences while the officer or director is, or was, serving at the Company’s request in such capacity. The maximum potential amount of future payments the Company could be required to make is unlimited; however, the Company has directors’ and officers’ insurance coverage that should limit its exposure and enable it to recover a portion of any future amounts paid. The Company is a party to a number of agreements entered into in the ordinary course of business that contain typical provisions that obligate the Company to indemnify the other parties to such agreements upon the occurrence of certain events. Such indemnification obligations are usually in effect from the date of execution of the applicable agreement for a period equal to the applicable statute of limitations. The aggregate maximum potential future liability of the Company under such indemnification provisions is uncertain. The Company leases office space under several noncancelable operating leases. The Company has standard indemnification arrangements under these leases that require it to indemnify the landlord against all costs, expenses, fines, suits, claims, demands, liabilities, and actions directly resulting from any breach, violation, or nonperformance of any covenant or condition of the respective lease. As of December 31, 2019 and 2018, the Company had not experienced any losses related to these indemnification obligations, and no material claims with respect thereto were outstanding. The Company does not expect significant claims related to these indemnification obligations and, consequently, concluded that the fair value of these obligations is negligible, and no related reserves have been established.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its consolidated financial position or results of operations upon adoption. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) Leases (Topic 842): Targeted Improvements In June 2018, the FASB issued ASU No. 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract In 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement In 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In December 2019, the FASB issued ASU No. 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes,” which is intended to simplify various aspects related to accounting for income taxes. The pronouncement is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2020, with early adoption permitted. ASU No. 2019-12 is effective for us beginning in fiscal 2021. The Company is currently in the process of evaluating the effects of this pronouncement on our financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Cash and Cash Equivalents	Cash and cash equivalents consist of the following at December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Cash and cash equivalents: Cash $ 415 $ 228 Money market funds 29,592 61,415 $ 30,007 $ 61,643
Summary of Estimated Useful Lives of Assets	These amounts are depreciated using the straight-line method over the estimated useful lives of the assets as follows: Laboratory equipment 4 years Computer equipment 3 years Software 5 years Leasehold improvements Shorter of useful life or remaining term of related lease
Summary of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share data): Years Ended December 31, 2019 2018 2017 Numerator: Net loss $ (47,339 ) $ (35,648 ) $ (21,650 ) Accretion of convertible preferred stock — — (58 ) Net loss attributable to common stockholders $ (47,339 ) $ (35,648 ) $ (21,708 ) Denominator: Weighted-average common shares – basic and diluted 22,180,868 20,741,226 4,520,337 Net loss per share attributable to common stockholders –basic and diluted $ (2.13 ) $ (1.72 ) $ (4.80 )
Summary of Anti-dilutive Securities Excluded from Calculation of Diluted Net Loss per Share	The following table sets forth the potentially dilutive securities that have been excluded from the calculation of diluted net loss per share because to include them would be anti-dilutive (in common stock equivalent shares): Years Ended December 31, 2019 2018 2017 Warrants 9,040 9,040 9,040 Stock options 3,915,591 2,141,527 1,508,124 Restricted stock units 517,750 — — Total 4,442,381 2,150,567 1,517,164

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value	The following tables present information about the Company’s financial assets and liabilities that have been measured at fair value at December 31, 2019 and 2018 and indicates the fair value hierarchy of the valuation inputs utilized to determine such fair value (in thousands): Description December 31, 2019 Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds, included in cash and cash equivalents $ 29,592 $ 29,592 $ — $ — Total assets $ 29,592 $ 29,592 $ — $ — Description December 31, 2018 Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds, included in cash and cash equivalents $ 61,415 $ 61,415 $ — $ — Total assets $ 61,415 $ 61,415 $ — $ —
Summary of Changes in Fair Value of Warrants, Represented a Recurring Measurement Classified Within Level 3 of Fair Value Hierarchy, using Significant Unobservable Inputs	The following table sets forth a summary of changes in the fair value of the Warrants, which represented a recurring measurement classified within Level 3 of the fair value hierarchy, wherein fair value was estimated using significant unobservable inputs (in thousands, except share data): Balance at December 31, 2016 $ 267 Change in fair value of Warrants through the date of the IPO included in other income (expense) 257 Fair value of Warrants reclassified to stockholders' equity (deficit) upon conversion to warrants for the conversion of common stock (524 ) Balance at December 31, 2017 $ —

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment includes the following at December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Property and equipment: Laboratory equipment $ 779 $ 728 Computer equipment 6 6 Software 39 39 824 773 Less: Accumulated depreciation (423 ) (259 ) Property and equipment, net $ 401 $ 514

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2019
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): December 31, 2019 2018 Payroll and employee-related expenses $ 1,250 $ 1,690 Third-party research and development expenses 1,393 1,514 Professional fees 229 299 Restructuring charges 373 — Loan interest 43 46 Other 82 76 Total accrued expenses $ 3,370 $ 3,625

Restructuring Charges (Tables)

Restructuring Charges (Tables)	12 Months Ended
	Dec. 31, 2019
Restructuring And Related Activities [Abstract]
Schedule of Components of Restructuring Charges	The following table outlines the components of the restructuring charges during the year ended December 31, 2019 included in the consolidated statement of operations, and ending liability recorded in the balance sheet as at December 31, 2019 (in thousands): Charges incurred during the year ended December 31, 2019 Amount paid through December 31, 2019 Remaining liability at December 31, 2019 Employee severance, bonus and other $ 605 $ (232 ) $ 373 Total restructuring charges $ 605 $ (232 ) $ 373

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Operating Leased Assets [Line Items]
Schedule of Future Minimum Commitments under Operating Leases	The following information is disclosed in accordance with ASC 840, Leases (Topic 840) 2019 $ 487 2020 539 2021 30 $ 1,056
ASC 842
Operating Leased Assets [Line Items]
Schedule of Maturities of Operating Lease Liabilities	Maturities of the Company’s operating lease liabilities in accordance with ASC 842 as of December 31, 2019 are as follows (in thousands): 2020 $ 498 2021 30 Total maturities $ 528 Less: Amount representing interest (16 ) Present value of operating lease liabilities $ 512

Loan and Security Agreement (Ta

Loan and Security Agreement (Tables)	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Summary of Minimum Aggregate Future Loan and Interest Payments	The minimum aggregate future loan and interest payments at December 31, 2019 are as follows (in thousands): Years Ending December 31, 2020 4,409 2021 4,208 2022 2,029 Total minimum payments 10,646 Less: Amount representing interest (645 ) Less: Discount (21 ) Less: Current portion (3,992 ) Loan payable, net of current portion $ 5,988

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Summary of Shares of Common Stock Reserved	The Company has reserved for future issuances the following shares of common stock as of December 31, 2019 and 2018: December 31, 2019 December 31, 2018 Warrants 9,040 9,040 Stock options and restricted stock units 5,070,303 4,262,341 Employee stock purchase plan 380,005 405,742 Total 5,459,348 4,677,123

Stock Incentive Plans (Tables)

Stock Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2019
Summary of Stock-based Compensation Expense	Stock-based compensation expense included in the Company’s statements of operations and comprehensive loss is as follows (in thousands): Years Ended December 31, 2019 2018 2017 Research and development $ 1,175 $ 584 $ 147 General and administrative 1,814 1,465 370 Total $ 2,989 $ 2,049 $ 517
Summary of Stock Option Activity	A summary of the stock option activity under the 2017 and 2011 Plans is as follows: Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2018 2,141,527 $ 4.32 7.7 $ 4,959 Granted 2,021,550 4.65 Exercised (24,399 ) 1.49 Cancelled (223,087 ) 7.35 Outstanding at December 31, 2019 3,915,591 $ 4.33 8.1 $ 1,921 Exercisable at December 31, 2019 1,686,341 $ 3.43 6.5 $ 1,589
Restricted Stock Units (RSUs)
Summary of Nonvested RSUs	Shares Weighted-Average Grant Date Fair Value Nonvested at January 1, 2019 — $ — Granted 517,750 2.42 Vested — — Forfeited — — Nonvested at December 31, 2019 517,750 $ 2.42
Employees and Directors
Schedule of Assumptions Used in Black-Scholes Option Pricing Model to Estimate Fair Value of Stock Options	The fair value of each stock option granted to employees and directors was estimated on the date of grant using the Black-Scholes option-pricing model, with the following range of assumptions for the years ended December 31, 2019, 2018 and 2017: Years Ended December 31, 2019 2018 2017 Risk-free interest rate 1.4% – 2.6% 2.3% – 3.1% 1.9% – 2.3% Expected dividend yield —% —% —% Expected term (in years) 5.5 – 6.8 5.5 – 6.1 5.6 – 6.3 Expected volatility 80% 81% 81%

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Summary of Deferred Tax Assets	The significant components of the Company’s deferred tax assets are comprised of the following (in thousands): December 31, 2019 2018 Deferred tax assets: Net operating loss carryforwards $ 42,549 $ 30,294 Research and development credits 8,138 5,843 Licenses 19 21 Stock based compensation 811 369 Operating lease liabilities 140 — Other 281 418 Total gross deferred tax assets 51,938 36,945 Less: Valuation allowance (51,800 ) (36,945 ) Net deferred tax assets 138 — Deferred tax liabilities: Operating lease assets (138 ) — Total gross deferred tax liabilities (138 ) — Net deferred taxes $ — $ —
Reconciliation of Income Taxes Computed at Statutory Federal Income Tax Rate to Income Taxes Reflected In Financial Statements	A reconciliation of income tax expense computed at the statutory federal income tax rate to income taxes reflected in the financial statements is as follows: 2019 2018 2017 Income tax computed at federal statutory tax rate 21.0 % 21.0 % 34.0 % Permanent differences — % — % (1.9 )% State taxes, net of federal benefit 6.1 % 6.2 % 4.8 % Research and development and other tax credits 4.9 % 3.1 % 5.0 % Stock based compensation (0.6 )% (0.5 )% (0.5 )% Federal rate change — % — % (42.7 )% Change in deferred tax asset valuation allowance (31.4 )% (29.8 )% 1.3 % — % — % — %

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	The following table contains quarterly financial information for 2019 and 2018. The Company believes that the following information reflects all normal recurring adjustments necessary for the fair statement of the information for the periods presented. 2019 First Quarter Second Quarter Third Quarter Fourth Quarter Total (in thousands, except per share amounts) Total operating expenses $ 11,559 $ 11,335 $ 13,338 $ 11,293 $ 47,525 Loss from operations (11,559 ) (11,335 ) (13,338 ) (11,293 ) (47,525 ) Net loss (11,419 ) (11,273 ) (13,288 ) (11,359 ) (47,339 ) Net loss attributable to common stockholders - basic and diluted $ (0.55 ) $ (0.54 ) $ (0.57 ) $ (0.47 ) $ (2.13 ) 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Total (in thousands, except per share amounts) Total operating expenses $ 7,973 $ 8,135 $ 9,705 $ 9,780 $ 35,593 Loss from operations (7,973 ) (8,135 ) (9,705 ) (9,780 ) (35,593 ) Net loss (7,880 ) (8,647 ) (9,510 ) (9,611 ) (35,648 ) Net loss attributable to common stockholders - basic and diluted $ (0.38 ) $ (0.42 ) $ (0.46 ) $ (0.46 ) $ (1.72 )

Organization and Basis of Pre_2

Organization and Basis of Presentation - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ 164,944	$ 117,605
Cash and cash equivalents	$ 30,007	$ 61,643

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
Entity incorporated date	Dec. 31, 2014
Impairment losses	$ 0	$ 0	$ 0
Income tax positions recognized, minimum percentage	50.00%
Operating lease, right-of-use assets	$ 549,000			$ 1,000,000
Operating lease, liabilities				1,000,000
Finance lease, right-of-use assets				0
Finance lease, liabilities				$ 0
Allena Pharmaceuticals Security Corporation
Summary Of Significant Accounting Policies [Line Items]
Entity incorporated date	Dec. 31, 2014
Allena Pharmaceuticals Ireland Limited
Summary Of Significant Accounting Policies [Line Items]
Entity incorporated date	Mar. 31, 2017

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Cash and cash equivalents:
Cash	$ 415	$ 228
Money market funds	29,592	61,415
Cash and Cash Equivalents, at Carrying Value	$ 30,007	$ 61,643

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Assets (Details)	12 Months Ended
	Dec. 31, 2019
Laboratory Equipment
Property, Plant and Equipment [Line Items]
Estimated useful life	4 years
Computer Equipment
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Software
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Estimated useful life, description	Shorter of useful life or remaining term of related lease

Summary of Significant Accoun_7

Summary of Significant Accounting Policies- Summary of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Details) - 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	$ (11,359)	$ (13,288)	$ (11,273)	$ (11,419)	$ (9,611)	$ (9,510)	$ (8,647)	$ (7,880)	$ (47,339)	$ (35,648)	$ (21,650)
Accretion of convertible preferred stock											(58)
Net loss attributable to common stockholders									$ (47,339)	$ (35,648)	$ (21,708)
Denominator:
Weighted-average common shares – basic and diluted									22,180,868	20,741,226	4,520,337
Net loss per share attributable to common stockholders — basic and diluted	$ (0.47)	$ (0.57)	$ (0.54)	$ (0.55)	$ (0.46)	$ (0.46)	$ (0.42)	$ (0.38)	$ (2.13)	$ (1.72)	$ (4.80)

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Summary of Anti-dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of loss per share	4,442,381	2,150,567	1,517,164
Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of loss per share	517,750
Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of loss per share	9,040	9,040	9,040
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of loss per share	3,915,591	2,141,527	1,508,124

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	$ 29,592	$ 61,415
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	29,592	61,415
Money market funds, included in cash and cash equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Money market funds, included in cash and cash equivalents	29,592	61,415
Money market funds, included in cash and cash equivalents | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Money market funds, included in cash and cash equivalents	$ 29,592	$ 61,415

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Change in valuation methods or transfers	$ 0	$ 0
Transfers within fair value hierarchy	$ 0	$ 0

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Changes in Fair Value of Warrants, Represented a Recurring Measurement Classified Within Level 3 of Fair Value Hierarchy, using Significant Unobservable Inputs (Details) - Warrants - Recurring - Level 3 $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance	$ 267
Change in fair value of Warrants through the date of the IPO included in other income (expense)	257
Fair value of Warrants reclassified to stockholders' equity (deficit) upon conversion to warrants for the conversion of common stock	$ (524)

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property and equipment:
Property and equipment, gross	$ 824	$ 773
Less: Accumulated depreciation	(423)	(259)
Property and equipment, net	401	514
Laboratory Equipment
Property and equipment:
Property and equipment, gross	779	728
Computer Equipment
Property and equipment:
Property and equipment, gross	6	6
Software
Property and equipment:
Property and equipment, gross	$ 39	$ 39

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Depreciation expense	$ 163,000	$ 78,000	$ 73,000

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Payroll and employee-related expenses	$ 1,250	$ 1,690
Third-party research and development expenses	1,393	1,514
Professional fees	229	299
Restructuring charges	373
Loan interest	43	46
Other	82	76
Total accrued expenses	$ 3,370	$ 3,625

Restructuring Charges - Additio

Restructuring Charges - Additional Information (Details) - USD ($) $ in Thousands	Nov. 29, 2019	Dec. 31, 2019
Restructuring And Related Activities [Abstract]
Restructuring charges, number of workforce headcount reduction percentage	38.00%
Restructuring expense at the time of workforce reduction	$ 600	$ 605

Restructuring Charges - Schedul

Restructuring Charges - Schedule of Components of Restructuring Charges (Details) - USD ($) $ in Thousands	Nov. 29, 2019	Dec. 31, 2019
Restructuring Cost And Reserve [Line Items]
Restructuring charges, Incurred during the year ended December 31, 2019	$ 600	$ 605
Restructuring charges, Amount paid through December 31, 2019		(232)
Restructuring charges, Remaining liability at December 31, 2019		373
Employee Severance, Bonus and Other
Restructuring Cost And Reserve [Line Items]
Restructuring charges, Incurred during the year ended December 31, 2019		605
Restructuring charges, Amount paid through December 31, 2019		(232)
Restructuring charges, Remaining liability at December 31, 2019		$ 373

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019USD ($)ft²shares	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Operating Leased Assets [Line Items]
Lease costs	$ 500,000
Operating lease, weighted average remaining lease term	1 year
Operating lease, weighted average discount rate	5.50%
Operating leases, rent expense, net		$ 500,000	$ 400,000
Althea Technologies, Inc
Operating Leased Assets [Line Items]
Contract termination period	60 days
Althea Technologies, Inc | License Agreement | Maximum
Operating Leased Assets [Line Items]
Potential milestone payable	$ 56,000,000
Patents | Althea Technologies, Inc | License Agreement
Operating Leased Assets [Line Items]
Fees and costs incurred	$ 100,000
Type of Cost, Good or Service [Extensible List]	us-gaap:LicenseMember
Common stock, shares issued | shares	88,186
Newton, MA
Operating Leased Assets [Line Items]
Rentable office space under operating lease | ft²	7,795
Base rent for office space	$ 300,000
Operating lease expiration date	Dec. 31, 2020
Sudbury, MA
Operating Leased Assets [Line Items]
Rentable office space under operating lease | ft²	7,564
Base rent for office space	$ 200,000
Operating lease expiration date	Feb. 28, 2021

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Lessee Lease Description [Line Items]
Present value of operating lease liabilities		$ 1,000
ASC 842
Lessee Lease Description [Line Items]
2020	$ 498
2021	30
Total maturities	528
Less: Amount representing interest	(16)
Present value of operating lease liabilities	$ 512

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Future Minimum Commitments under Operating Leases (Details) $ in Thousands	Dec. 31, 2018USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2019	$ 487
2020	539
2021	30
Total future operating lease commitment	$ 1,056

Loan and Security Agreement - A

Loan and Security Agreement - Additional Information (Details) - USD ($)	Jun. 29, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Loss on extinguishment of debt			$ 617,000
Loan Agreement | SVB
Debt Instrument [Line Items]
Outstanding loan amount				$ 9,700,000
Percentage of final payment based on total borrowings		8.25%
Repayment of outstanding principal balance	$ 7,700,000
Loss on extinguishment of debt	600,000
Loan Agreement | PWB
Debt Instrument [Line Items]
Loan agreement, maximum borrowing capacity	12,000,000
Loan agreement, advanced amount	10,000,000
Loan agreement, remaining borrowing capacity	$ 2,000,000
Loan agreement, interest rate above prime rate	5.00%
Loan agreement, term	48 months
Loan agreement, interest only payment period	18 months
Expiration of initial interest only period	Dec. 31, 2019
Loan agreement, number of monthly payments	30 months
Loan agreement, frequency of payments		monthly
Aggregate gross proceeds for success fee to be paid	$ 25,000,000
Success fee payable	$ 300,000

Loan and Security Agreement - S

Loan and Security Agreement - Summary of Minimum Aggregate Future Loan and Interest Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
2020	$ 4,409
2021	4,208
2022	2,029
Total minimum payments	10,646
Less: Amount representing interest	(645)
Less: Discount	(21)
Less: Current portion	(3,992)
Loan payable, net of current portion	$ 5,988	$ 9,980

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 30, 2019	Jun. 28, 2019	Dec. 01, 2017	Nov. 06, 2017	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Common stock, shares issued					24,735,009	20,809,025
Common stock, voting rights					one vote for each share held
Warrants exercisable shares					9,040	9,040
Exercise price of warrants					$ 11.06	$ 11.06
Warrants expiration date					May 1, 2026
ATM Agreement | Cowen
Class of Stock [Line Items]
Net proceeds after deducting underwriting discounts and commissions and offering costs	$ 2.6
Sales proceeds of common stock						$ 50
Payments for commissions						3.00%
Common stock, shares issued	1,200,000
Initial Public Offering
Class of Stock [Line Items]
Issuance of common stock, net of issuance costs, shares				5,333,333
Issuance price per shares				$ 14
Gross proceeds from issuance of common stock				$ 74.7
Net proceeds after deducting underwriting discounts and commissions and offering costs				67
Underwriting discounts and commissions and offering costs				$ 7.9
Convertible preferred stock converted into common stock				13,945,509
Over-allotment Option
Class of Stock [Line Items]
Issuance of common stock, net of issuance costs, shares			16,969
Gross proceeds from issuance of common stock			$ 0.2
Direct Offering
Class of Stock [Line Items]
Issuance of common stock, net of issuance costs, shares		2,632,092
Issuance price per shares		$ 3.80
Gross proceeds from issuance of common stock		$ 10
Net proceeds after deducting underwriting discounts and commissions and offering costs		$ 9.4

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Shares of Common Stock Reserved (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Shares of common stock reserved for future issuances	5,459,348	4,677,123
Warrants
Class of Stock [Line Items]
Shares of common stock reserved for future issuances	9,040	9,040
Stock Options and Restricted Stock Units
Class of Stock [Line Items]
Shares of common stock reserved for future issuances	5,070,303	4,262,341
Employee Stock Purchase Plan
Class of Stock [Line Items]
Shares of common stock reserved for future issuances	380,005	405,742

Stock Incentive Plans - Additio

Stock Incentive Plans - Additional Information (Details) - USD ($)	Jan. 01, 2020	Dec. 02, 2019	Jan. 01, 2019	Jan. 01, 2018	Oct. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expense related to awards granted						$ 2,989,000	$ 2,049,000	$ 517,000
Total intrinsic value of options exercised						$ 58,000	$ 1,200,000	$ 276,000
Shares of common stock reserved for future issuances						5,459,348	4,677,123
Employees and Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average fair value of options granted						$ 3.29	$ 6.21	$ 6.16
Non-Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock options granted						0	0
Stock Options | Employees and Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expense related to awards granted						$ 2,900,000	$ 1,900,000	$ 500,000
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expense related to awards granted						100,000
Share-based compensation awards, number of shares employees and officers		517,750
Share-based payment arrangement, nonvested award, unrecognized, amount						$ 1,200,000
Restricted Stock Units (RSUs) | Vesting on June 2, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation awards, vesting percent						50.00%
Restricted Stock Units (RSUs) | Vesting on December 2, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation awards, vesting percent						50.00%
2011 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for grant					0
2011 Plan | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based award, vesting period						4 years
2011 Plan | Stock Options | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based award, expiration period						10 years
2017 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option grant effective date					Oct. 31, 2017
Share based award, description						The Company adopted the 2017 Stock Option and Incentive Plan (“2017 Plan”) on October 31, 2017. Upon adoption of the 2017 Plan, no further grants were made under the 2011 Stock Incentive Plan (“2011 Plan”). The 2017 Plan initially provided for the grant of awards for 2,038,021 shares of common stock. In addition to the shares available for grant under the 2017 Plan, any awards outstanding under the 2011 Plan as of the October 31, 2017 that are cancelled, forfeited or otherwise terminated without being exercised, the number of shares underlying such awards are available for future grant under the 2017 Plan. The 2017 Plan also provides that an additional number of shares will automatically be added to the shares authorized for issuance under the 2017 Plan on January 1 of each year. The number of shares added each year will be equal to the lesser of: (i) 4% of the outstanding shares on the immediately preceding December 31 or (ii) such amount as determined by the Compensation Committee of the registrant’s Board of Directors. On January 1, 2018, 2019 and 2020, the shares available for grant under the 2017 Plan was automatically increased by 827,786, 832,361 and 989,400 shares, respectively.
Percentage criteria for additional shares granted					4.00%
Additional shares available for grant			832,361	827,786
2017 Plan | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future grant						636,962
Stock-based award, vesting period						4 years
2017 Plan | Stock Options | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based award, expiration period						10 years
2017 Plan | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for grant					2,038,021
2017 Plan | Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional shares available for grant	989,400
2017 And 2011 Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock options granted						2,021,550
Unrecognized stock-based compensation expense related to unvested employee stock options						$ 7,100,000
Unrecognized stock-based compensation expense, weighted average period for recognition						2 years 9 months 18 days
2017 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based award, description						The Company adopted the 2017 Employee Stock Purchase Plan (“ESPP”) on October 31, 2017. The ESPP permits eligible employees to enroll in six-month offering periods. Participants may purchase shares of the Company’s common stock, through payroll deductions, at a price equal to 85% of the fair market value of the common stock on the first or last day of the applicable six-month offering period, whichever is lower. Purchase dates under the ESPP occur on or about January 1 and July 1 each year. The ESPP initially reserved 206,284 shares of common stock for issuance. The ESPP also provides that an additional number of shares will automatically be added to the shares authorized for issuance under the ESPP on January 1 of each year. The number of shares added each year will be equal to the lesser of: (i) 1% of the outstanding shares on the immediately preceding December 31 or (ii) such amount as determined by the Compensation Committee of the registrant’s Board of Directors. On January 1, 2018 the shares available for grant under the ESPP was automatically increased by 206,946 shares. shares were added to the ESPP on January 1, 2019 and 2020.
Percentage criteria for additional shares granted					1.00%
Additional shares available for grant				206,946
ESPP effective date					Oct. 31, 2017
Initial offering period						The ESPP permits eligible employees to enroll in six-month offering periods.
Offering period permitted under plan for enrollment					6 months
Purchase price of common stock, percent					85.00%
Shares of common stock reserved for future issuances					206,284	380,005
Amount withheld from employees for purchase of common stock shares under plan						$ 76,000	$ 35,000
Common stock shares available for purchase under plan						25,737	7,488

Stock Incentive Plans - Summary

Stock Incentive Plans - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 2,989	$ 2,049	$ 517
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	1,175	584	147
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 1,814	$ 1,465	$ 370

Stock Incentive Plans - Schedul

Stock Incentive Plans - Schedule of Assumptions Used in Black-Scholes Option Pricing Model to Estimate Fair Value of Stock Options (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	1.40%
Risk-free interest rate, maximum	2.60%
Expected volatility, minimum	80.00%
Expected volatility, maximum	83.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 9 months 18 days
Stock Options | Employees and Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum		2.30%	1.90%
Risk-free interest rate, maximum		3.10%	2.30%
Expected volatility, minimum		81.00%	81.00%
Expected volatility, maximum		89.00%	87.00%
Stock Options | Minimum | Employees and Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)		5 years 6 months	5 years 7 months 6 days
Stock Options | Maximum | Employees and Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)		6 years 1 month 6 days	6 years 3 months 18 days

Stock Incentive Plans - Summa_2

Stock Incentive Plans - Summary of Stock Option Activity (Details) - 2017 And 2011 Plans - 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, Outstanding, Beginning balance	2,141,527
Shares, Granted	2,021,550
Shares, Exercised	(24,399)
Shares, Cancelled	(223,087)
Shares, Outstanding, Ending balance	3,915,591	2,141,527
Shares, Exercisable	1,686,341
Weighted-Average Exercise Price, Outstanding, Beginning balance	$ 4.32
Weighted-Average Exercise Price, Granted	4.65
Weighted-Average Exercise Price, Exercised	1.49
Weighted-Average Exercise Price, Cancelled	7.35
Weighted-Average Exercise Price, Outstanding, Ending balance	4.33	$ 4.32
Weighted-Average Exercise Price, Exercisable	$ 3.43
Weighted-Average Remaining Contractual Life (in years), Outstanding	8 years 1 month 6 days	7 years 8 months 12 days
Weighted-Average Remaining Contractual Life (in years), Exercisable	6 years 6 months
Aggregate Intrinsic Value, Outstanding	$ 1,921	$ 4,959
Aggregate Intrinsic Value, Exercisable	$ 1,589

Stock Incentive Plans - Summa_3

Stock Incentive Plans - Summary of Nonvested RSUs (Details) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Granted | shares	517,750,000
Shares, Outstanding, Ending balance | shares	517,750,000
Weighted-Average Grant Date Fair Value, Granted | $ / shares	$ 2.42
Weighted-Average Grant Date Fair Value, Outstanding, Ending balance | $ / shares	$ 2.42

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	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
Operating Loss Carryforwards [Line Items]
Net loss	$ (11,359,000)	$ (13,288,000)	$ (11,273,000)	$ (11,419,000)	$ (9,611,000)	$ (9,510,000)	$ (8,647,000)	$ (7,880,000)	$ (47,339,000)	$ (35,648,000)	$ (21,650,000)
Income tax benefit									0	0	$ 0
Valuation allowance	51,800,000				36,945,000				51,800,000	36,945,000
Valuation allowances period increase (decrease)									14,900,000	10,600,000
Accrued interest and penalties related to uncertain tax positions	0				0				$ 0	0
Income tax examination, description									The federal, state and foreign income tax returns are generally subject to tax examinations for the tax years ended December 31, 2016 through December 31, 2019.
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	155,900,000				111,100,000				$ 155,900,000	111,100,000
Operating loss carryforwards with an indefinite life	78,000,000								78,000,000
Operating loss carryforwards subject to expiration	77,900,000								$ 77,900,000
Operating loss carryforwards expiration period									2037
Federal | Research and Development
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	5,900,000				4,000,000				$ 5,900,000	4,000,000
Tax credit carryforward expiration period									2039
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	155,000,000				110,300,000				$ 155,000,000	110,300,000
Operating loss carryforwards expiration period									2039
State | Research and Development
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	$ 2,800,000				$ 2,200,000				$ 2,800,000	$ 2,200,000
Tax credit carryforward expiration period									2034

Income Taxes - Summary of Defer

Income Taxes - Summary of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 42,549	$ 30,294
Research and development credits	8,138	5,843
Licenses	19	21
Stock based compensation	811	369
Operating lease liabilities	140
Other	281	418
Total gross deferred tax assets	51,938	36,945
Less: Valuation allowance	(51,800)	$ (36,945)
Net deferred tax assets	138
Deferred tax liabilities:
Operating lease assets	(138)
Total gross deferred tax liabilities	$ (138)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Taxes Computed at Statutory Federal Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory tax rate	21.00%	21.00%	34.00%
Permanent differences			(1.90%)
State taxes, net of federal benefit	6.10%	6.20%	4.80%
Research and development and other tax credits	4.90%	3.10%	5.00%
Stock based compensation	(0.60%)	(0.50%)	(0.50%)
Federal rate change			(42.70%)
Change in deferred tax asset valuation allowance	(31.40%)	(29.80%)	1.30%

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Details) - USD ($) $ in Millions	Jan. 01, 2019	Dec. 31, 2019
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Maximum annual contribution per employee		100.00%
Defined contribution plan, description		Participants may contribute up to 100% of their annual compensation to the 401(k) Plan, subject to statutory limitations. Through December 31, 2018, the 401(k) Plan did not allow the Company to make matching contributions. Effective January 1, 2019, the Company amended the 401(k) Plan to allow the Company to make matching contributions.
Employer contribution percentage	100.00%
Employer matching contribution, percent of employees' salary	4.00%
Employer matching contribution cost		$ 0.3

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Information (Details) - 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
Income Statement [Abstract]
Total operating expenses	$ 11,293	$ 13,338	$ 11,335	$ 11,559	$ 9,780	$ 9,705	$ 8,135	$ 7,973	$ 47,525	$ 35,593	$ 20,950
Loss from operations	(11,293)	(13,338)	(11,335)	(11,559)	(9,780)	(9,705)	(8,135)	(7,973)	(47,525)	(35,593)
Net loss	$ (11,359)	$ (13,288)	$ (11,273)	$ (11,419)	$ (9,611)	$ (9,510)	$ (8,647)	$ (7,880)	$ (47,339)	$ (35,648)	$ (21,650)
Net loss attributable to common stockholders - basic and diluted	$ (0.47)	$ (0.57)	$ (0.54)	$ (0.55)	$ (0.46)	$ (0.46)	$ (0.42)	$ (0.38)	$ (2.13)	$ (1.72)	$ (4.80)