Allena Pharmaceuticals (ALNAQ) 10-K 7 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Mar. 01, 2019	Jun. 29, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	ALNA
Entity Registrant Name	ALLENA PHARMACEUTICALS, INC.
Entity Central Index Key	1,624,658
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	No
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		20,815,014
Entity Public Float			$ 150,081,377

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 61,643	$ 94,494
Prepaid expenses and other current assets	2,826	1,539
Total current assets	64,469	96,033
Property and equipment, net	514	127
Other assets	246	89
Total assets	65,229	96,249
Current liabilities:
Accounts payable	2,138	1,724
Loan payable, net of discount		3,870
Accrued expenses	3,625	1,949
Total current liabilities	5,763	7,543
Loan payable, net of current portion and discount	9,980	5,516
Other liabilities	30	320
Total liabilities	15,773	13,379
Commitments and contingencies (Note 11)
Stockholders’ equity:
Common stock, $0.001 par value; 125,000,000 shares authorized; 20,809,025 and 20,694,658 shares issued and outstanding at December 31, 2018 and 2017, respectively	21	20
Additional paid-in capital	167,040	164,807
Accumulated deficit	(117,605)	(81,957)
Total stockholders’ equity	49,456	82,870
Total liabilities and stockholders’ equity	65,229	96,249
Undesignated Preferred Stock
Stockholders’ equity:
Undesignated preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued or outstanding

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	20,809,025	20,694,658
Common stock, shares outstanding	20,809,025	20,694,658
Undesignated Preferred Stock
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

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development	$ 26,376	$ 15,519	$ 20,103
General and administrative	9,217	5,431	4,083
Total operating expenses	35,593	20,950	24,186
Other income (expense):
Interest income (expense), net	575	(443)	(200)
Other income (expense), net	(13)	(257)	(121)
Loss on extinguishment of debt	(617)
Other income (expense), net	(55)	(700)	(321)
Net loss	$ (35,648)	$ (21,650)	$ (24,507)
Net loss per share attributable to common stockholders — basic and diluted	$ (1.72)	$ (4.80)	$ (18.35)
Weighted-average common shares outstanding — basic and diluted	20,741,226	4,520,337	1,339,254
Comprehensive loss:
Net loss	$ (35,648)	$ (21,650)	$ (24,507)
Other comprehensive income (loss):
Unrealized loss on investments			(2)
Total other comprehensive loss			(2)
Comprehensive loss	$ (35,648)	$ (21,650)	$ (24,509)

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, 2015		$ 17,959	$ 24,913	$ 52,786
Balance, Shares at Dec. 31, 2015		18,367,344	19,841,270	20,000,000
Balance at Dec. 31, 2015	$ (34,969)				$ 1	$ 830		$ (35,800)
Balance, Shares at Dec. 31, 2015					1,315,940
Exercise of common stock options	19				$ 0	19
Exercise of common stock options, shares					24,770
Vesting of restricted common stock, shares					675
Accretion of convertible preferred stock to redemption value		$ 8	$ 18	$ 43
Accretion of convertible preferred stock to redemption value	(69)					(69)
Stock-based compensation	251					251
Change in unrealized gain (loss) on available for sale investments	(2)						$ (2)
Net loss	(24,507)							(24,507)
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	95,785				$ 14	95,771
Conversion of preferred stock into common stock, shares					13,945,509
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 at Dec. 31, 2017	$ 82,870				$ 20	164,807		(81,957)
Balance, Shares at Dec. 31, 2017	20,694,658				20,694,658
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 at Dec. 31, 2018	$ 49,456				$ 21	$ 167,040		$ (117,605)
Balance, Shares at Dec. 31, 2018	20,809,025				20,809,025

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (35,648,000)	$ (21,650,000)	$ (24,507,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	2,049,000	517,000	251,000
Depreciation expense	78,000	73,000	46,000
Non-cash interest expense	161,000	351,000	204,000
Amortization of premium on investments		33,000	153,000
Loss on extinguishment of debt	617,000
Change in fair value of warrant liability		257,000	132,000
Changes in assets and liabilities:
Prepaid expenses and other current assets	(1,287,000)	(984,000)	343,000
Other assets	(34,000)	(89,000)
Accounts payable	441,000	199,000	(525,000)
Accrued expenses	1,764,000	228,000	689,000
Other liabilities	20,000		(180,000)
Net cash used in operating activities	(31,839,000)	(21,065,000)	(23,394,000)
Cash flows from investing activities:
Purchases of property and equipment	(318,000)	(57,000)	(102,000)
Purchases of investments		(1,247,000)	(53,210,000)
Maturities of investments		24,721,000	29,550,000
Net cash (used in) provided by investing activities	(318,000)	23,417,000	(23,762,000)
Cash flows from financing activities:
Proceeds from (payments of issuance costs) the issuance of common stock, net of issuance costs	(309,000)	67,197,000
Proceeds from exercise of stock options	139,000	28,000	19,000
Proceeds from issuance of stock through ESPP	34,000
Proceeds from loan payable	10,000,000		10,000,000
Repayment of loan payable	(10,492,000)	(333,000)	(6,256,000)
Debt issuance costs paid	(33,000)		(368,000)
Other	(33,000)
Net cash (used in) provided by financing activities	(694,000)	66,892,000	3,395,000
Net (decrease) increase in cash and cash equivalents	(32,851,000)	69,244,000	(43,761,000)
Cash and cash equivalents, beginning of period	94,494,000	25,250,000	69,011,000
Cash and cash equivalents, end of period	61,643,000	94,494,000	25,250,000
Supplemental disclosure of non-cash activities:
Cash paid for interest	906,000	452,000	472,000
Property and equipment purchases included in accounts payable	$ 72,000	11,000	38,000
Initial public offering costs included in accounts payable and accrued expenses		199,000
Issuance of warrants in connection with loan payable			67,000
Accretion of convertible preferred stock to redemption value		$ 58,000	$ 69,000

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2018
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. The Company has an accumulated deficit of $117.6 million at December 31, 2018, 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, 2018, the Company had $61.6 million of cash and cash equivalents. The Company believes its cash and cash equivalents as of December 31, 2018 will be sufficient to fund the Company's operating plan for a period of at least one year from the issuance date of the consolidated financial statements. Thereafter, the Company will be required to obtain additional funding in the future to achieve its operating plan. There can be no assurances, however, that the current operating plan will be achieved or that additional funding will be available on terms acceptable to the Company, or at all. 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, 2018
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, fair value of common stock prior to the closing of the Company’s IPO, valuation of share-based awards and the fair value of warrants prior to the conversion into warrants for the purchase of common stock upon the closing of the IPO. Actual results could differ from those estimates. The Company utilized significant estimates and assumptions in determining the fair value of its common stock prior to the Company’s IPO. The Company utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation 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, 2018 and 2017. The Company recognized other comprehensive loss of $2,000 for the year ended December 31, 2016 related to unrealized loss on available-for-sale investments. 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 market value. Cash and cash equivalents consist of the following at December 31, 2018 and 2017 (in thousands): December 31, 2018 2017 Cash and cash equivalents: Cash $ 228 $ 749 Money market funds 61,415 93,745 $ 61,643 $ 94,494 Investments The Company invests available cash primarily in U.S. and foreign corporate debt securities and United States government treasury securities. 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, 2018 and 2017. 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, 2018, 2017 and 2016. Warrants to Purchase Shares Subject to Redemption Prior to the closing of the IPO, the Company accounted for warrant instruments that either conditionally or unconditionally obligate the issuer to transfer assets as liabilities regardless of the timing of the redemption feature or price, even though the underlying shares may be classified as equity. These warrants were subject to revaluation at each balance sheet date, and any changes in fair value were recorded as a component of other income (expense) in the statements of operations and comprehensive loss. Upon the closing of the IPO, the warrants met the criteria to be classified in stockholders’ equity and the fair value of the warrant liability as of the IPO date was reclassified to stockholders’ equity (deficit). 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 In the first quarter of 2017, the Company made an accounting policy election to recognize forfeitures as they occur upon adoption of guidance per ASU No. 2016-09, Compensation – Stock Compensation The Company expenses the fair value of its share-based compensation awards to employees on a straight-line basis over the requisite service period, which is generally the vesting period. Stock-based compensation awards to non-employees are adjusted through stock-based compensation expense at each reporting period end to reflect the current fair value of such awards and are expensed on a straight-line basis. 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, 2018 2017 2016 Numerator: Net loss $ (35,648 ) $ (21,650 ) $ (24,507 ) Accretion of convertible preferred stock — (58 ) (69 ) Net loss attributable to common stockholders $ (35,648 ) $ (21,708 ) $ (24,576 ) Denominator: Weighted-average common shares – basic and diluted 20,741,226 4,520,337 1,339,254 Net loss per share attributable to common stockholders –basic and diluted $ (1.72 ) $ (4.80 ) $ (18.35 ) 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, 2018 2017 2016 Series A convertible preferred stock — — 4,400,410 Series B convertible preferred stock — — 4,753,536 Series C convertible preferred stock — — 4,791,563 Warrants 9,040 9,040 43,265 Stock options 2,141,527 1,508,124 1,348,845 Total 2,150,567 1,517,164 15,337,619 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, 2018 and 2017, 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 August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash In May 2017, the FASB issued ASU No. 2017-09, Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) Recently Issued Accounting Pronouncements 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 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

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 and indicates the fair value hierarchy of the valuation inputs utilized to determine such fair value (in thousands): 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 $ — $ — Description December 31, 2017 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 $ 93,745 $ 93,745 $ — $ — Total assets $ 93,745 $ 93,745 $ — $ — At December 31, 2018 and 2017, 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, 2018 and 2017. There were no transfers within the fair value hierarchy during the years ended December 31, 2018 and 2017. 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. The estimated fair value of the Warrants was determined using the Black-Scholes option-pricing model. A significant input to the fair value of the warrants is the fair value of the Series A and C Convertible Preferred Stock which was determined based upon the Company’s common stock valuations. The fair value of the Warrants was remeasured at each reporting date through the date of the 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, 2018
Property Plant And Equipment [Abstract]
Property and Equipment, Net	4. Property and Equipment, Net Property and equipment includes the following at December 31, 2017 and 2016 (in thousands): December 31, 2018 2017 Property and equipment: Laboratory equipment $ 728 $ 263 Computer equipment 6 6 Software 39 39 773 308 Less: Accumulated depreciation (259 ) (181 ) Property and equipment, net $ 514 $ 127 The Company recognized $78,000, $73,000 and $46,000 of depreciation expense for the years ended December 31, 2018, 2017 and 2016, respectively.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses consist of the following (in thousands): December 31, 2018 2017 Payroll and employee-related expenses $ 1,690 $ 1,132 Third-party research and development expenses 1,514 135 Professional fees 299 420 Loan interest 46 40 IPO-related costs — 111 Other 76 111 Total accrued expenses $ 3,625 $ 1,949

Loan and Security Agreement

Loan and Security Agreement	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Loan and Security Agreement	6. 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 borrowings were secured by a lien on all Company assets, excluding intellectual property. The May 2016 and December 2016 advances had a floating per annum interest rate of the greater of 4.0% or 0.5% above the prime rate. Principal payments were due through May 2020. At its option, the Company could prepay all, but not less than all, of the outstanding borrowings subject to a prepayment premium as defined in the 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 are available to the Company through one additional advance request until the end of the interest only period as defined below. 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 initial interest only period of 18 months. If the Company receives at least $50M of gross proceeds from the sale of its equity securities or upfront cash payment from a strategic partnership prior the expiration of the initial interest only period, the interest only period will be extended an additional six months. Upon the expiration of the initial interest only period on December 31, 2019, amounts borrowed will be repaid over 30 equal monthly payments of principal plus accrued but unpaid interest. If the interest only period is extended an additional six months, amounts borrowed will be repaid over 24 equal monthly payments of principal plus accrued but unpaid interest beginning July 1, 2020. 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 will be paid to the Lender. If the gross proceeds are received on or before June 30, 2019, the Success Fee is $200,000, and if the gross proceeds are received after June 30, 2019, the Success Fee is $300,000. 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, 2018. The minimum aggregate future loan and interest payments at December 31, 2018 are as follows (in thousands): Years Ending December 31, 2019 $ 550 2020 4,450 2021 4,229 2022 2,032 Total minimum payments 11,261 Less: Amount representing interest (1,261 ) Less: Discount (20 ) Less: Current portion — Loan payable, net of current portion $ 9,980

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	7. 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. 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, 2018 and 2017: December 31, 2018 December 31, 2017 Warrants 9,040 9,040 Stock options 4,262,341 3,538,345 Employee stock purchase plan 405,742 206,284 Total 4,677,123 3,753,669 Warrants At December 31, 2018 and 2017, 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, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Incentive Plans	8. 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 and 2019, the shares available for grant under the 2017 Plan was automatically increased by 827,786 and 832,361 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, 2018, 2,120,814 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, 2018 2017 2016 Research and development $ 584 $ 147 $ 68 General and administrative 1,465 370 183 Total $ 2,049 $ 517 $ 251 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, 2018, 2017 and 2016: Years Ended December 31, 2018 2017 2016 Risk-free interest rate 2.3% – 3.1% 1.9% – 2.3% 1.3% – 1.7% Expected dividend yield —% —% —% Expected term (in years) 5.5 – 6.1 5.6 – 6.3 5.4 – 6.4 Expected volatility 81% 81% 77% The expense related to awards granted to employees and directors for their service on the Board of Directors was $1.9 million, $0.5 million, and $0.2 million for the years ended December 31, 2018, 2017 and 2016, respectively. The Company did not grant any stock options to non-employees during the years ended December 31, 2018 or 2017.The fair value of each stock option granted to non-employees was estimated on the date of grant using the Black-Scholes option-pricing model. The expense related to awards granted to non-employees was $0.1 million, $65,000 and $24,000 for the years ended December 31, 2018 and 2017 and 2016, respectively. 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, 2017 1,508,124 $ 1.89 7.9 $ 12,328 Granted 801,474 8.57 Exercised (106,879 ) 1.29 Cancelled (61,192 ) 5.73 Outstanding at December 31, 2018 2,141,527 $ 4.32 7.7 $ 4,959 Exercisable at December 31, 2018 1,163,352 $ 2.07 6.9 $ 4,115 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, 2018, 2017 and 2016 was $6.21, $6.16 and $1.13 per share, respectively. The weighted-average fair value of options granted to non-employees during the year ended December 31, 2016 was $1.38 per share. 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, 2018, 2017 and 2016 was $1.2 million, $276,000 and $21,000, respectively. As of December 31, 2018, total unrecognized stock-based compensation expense relating to unvested stock options was $4.4 million. This amount is expected to be recognized over a weighted-average period of 2.8 years. 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. During the year ended December 31, 2018, $35,000 was withheld from employees, on an after-tax basis, in order to purchase 7,488 shares of the Company’s common stock. As of December 31, 2018, 405,742 shares of Company’s common stock remained available for issuance under the ESPP.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes New Tax Legislation On December 22, 2017, the President of the United States signed into law the Tax Cuts and Jobs Act (“TCJA”). This legislation reduced the U.S. corporate tax rate from the current rate of 34% to 21% for tax years beginning after December 31, 2017. As a result of the enacted law, the Company was required to revalue deferred tax assets and liabilities existing as of December 31, 2017 from the 34% federal rate in effect through the end of 2017, to the new 21% rate. The Company has recognized the impact of the Tax Reform Act in these consolidated financial statements and related disclosures. Due to the complexities involved in accounting for the enactment of the Tax Reform Act, the SEC staff issued Staff Accounting Bulletin No. 118 ("SAB 118"), which allows a registrant to record provisional amounts during a measurement period not to extend beyond one year of the enactment date. In accordance with SAB 118, the Company recorded provisional amounts reflecting the impact of the Tax Reform Act in these consolidated financial statements and related disclosures. The impact of the remeasurement of the Company’s U.S. deferred tax assets and liabilities to 21% resulted in the reduction of deferred tax assets of approximately $9.3 million, which is offset by a full valuation allowance. There was no impact to the Company’s income statement due to the reduction in the U.S. corporate tax rate. 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 year ended December 31, 2018, the Company recorded a net loss of approximately $35.6 million and, since it maintains a full valuation allowance on its deferred tax assets, the Company did not record an income tax benefit for the year ended December 31, 2018. 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, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 30,294 $ 21,190 Research and development credits 5,843 4,732 Licenses 21 24 Stock based compensation 369 70 Other 418 300 Total gross deferred tax asset 36,945 26,316 Less: Valuation allowance (36,945 ) (26,316 ) Net deferred tax asset $ — $ — 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, 2018 and 2017, 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 $36.9 million and $26.3 million has been established at December 31, 2018 and 2017, respectively. The valuation allowance increased by approximately $10.6 million during the year ended December 31, 2018 due primarily to the generation of net operating losses and decreased by approximately $0.3 million in the year ended December 31, 2017 due primarily to the revaluation of the deferred tax assets at a 21% Federal tax rate. 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: 2018 2017 2016 Income tax computed at federal statutory tax rate 21.0 % 34.0 % 34.0 % Permanent differences — % (1.9 )% (0.2 )% State taxes, net of federal benefit 6.2 % 4.8 % 5.1 % Research and development and other tax credits 3.1 % 5.0 % 6.1 % Stock based compensation (0.5 )% (0.5 )% (0.3 )% Federal rate change — % (42.7 )% — % Change in deferred tax asset valuation allowance (29.8 )% 1.3 % (44.7 )% — % — % — % As of December 31, 2018 and 2017, the Company had U.S. federal net operating loss carryforwards of approximately $111.1 million and $77.9 million, respectively, which may be available to offset future income tax liabilities and expire at various dates through 2037. As of December 31, 2018 and 2017, the Company also had U.S. state net operating loss carryforwards of approximately $110.3 million and $76.5 million, respectively, which may be available to offset future income tax liabilities and expire at various dates through 2038. As of December 31, 2018 and 2017, the Company had federal research and development tax credit carryforwards of approximately $4.0 million and $3.3 million, respectively, available to reduce future tax liabilities which expire at various dates through 2038. As of December 31, 2018 and 2017, the Company had state research and development tax credit carryforwards of approximately $2.2 million and $1.9 million, respectively, available to reduce future tax liabilities which expire at various dates through 2033. 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, 2018. 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, 2018 and 2017, 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.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	10. Related Party Transactions From September 2015 to June 2017, the Company received consulting and management services from one of its investors, Third Rock Ventures LLP (“Third Rock Ventures”). The Company paid Third Rock Ventures $2,000 and $69,000 for these services during the years ended December 31, 2017 and 2016, respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies In August 2011 and October 2013, the Company and an independent third party entered into operating leases for approximately 6,055 square feet of office space in Newton, MA (“Newton Lease”) and approximately 3,170 square feet of laboratory space in Natick, MA, respectively. Base rent for the office space during the initial rent period was approximately $0.1 million per year and increased annually. Base rent for the lab space was approximately $59,000 annually. Rent expense, inclusive of the escalating rent payments and free rent period, was recognized on a straight-line basis over the term of each lease agreement. The Company and the independent third party were each jointly and severally liable for the obligations under both leases. In October 2016, the Newton lease was amended to extend the term one year to May 2018 and, effective June 1, 2017 removed the independent third party from the lease and all related obligations of the lease. In December 2017, the Newton lease was amended again to increase the amount of office space to approximately 7,795 square feet and extend the term to December 31, 2020. The amended lease for laboratory space expired October 31, 2017. In August 2016, the Company entered into an operating lease for approximately 3,890 square feet of laboratory space in Sudbury, MA. This lease was to expire in August 2017. In February 2017, the Company amended this lease to extend the term to February 2019 and increase the amount of rentable space to approximately 5,133 square feet, with an option to lease another 2,029 square feet. In March 2018, this lease was amended again to reduce rentable space to approximately 4,636 square feet and extend the term to February 2021. The Company accounted for these amendments as modifications to the original lease agreement. In August 2018, this lease was again amended to add approximately 2,928 square feet of office space. Base rent for this space is approximately $0.2 million annually. Rent expense includes the Company’s allocated portion of rental obligations under the leases. The Company recorded $0.5 million, $0.4 million and $0.2 million, of rent expense for the years ended December 31, 2018, 2017 and 2016, respectively. The minimum aggregate future operating lease commitments at December 31, 2018 are as follows (in thousands): December 31, 2018 2019 $ 487 2020 539 2021 30 $ 1,056

License Agreement

License Agreement	12 Months Ended
	Dec. 31, 2018
License Agreement [Abstract]
License Agreement	12. 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 $56.0 million. The Company may terminate the agreement at any time with 60 days prior written notice.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2018
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Employee Benefit Plan	13. 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 will match 100% of employee contributions up to a maximum of 4% of employees’ salary. Matching contributions are fully vested at the time of contribution.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	14. Selected Quarterly Financial Data (Unaudited) The following table contains quarterly financial information for 2018 and 2017. 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. 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 ) 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Total (in thousands, except per share amounts) Total operating expenses $ 5,542 $ 4,475 $ 4,362 $ 6,571 $ 20,950 Loss from operations (5,542 ) (4,475 ) (4,362 ) (6,571 ) (20,950 ) Net loss (5,671 ) (4,632 ) (4,670 ) (6,677 ) (21,650 ) Net loss attributable to common stockholders - basic and diluted $ (4.24 ) $ (3.46 ) $ (3.49 ) $ (0.48 ) $ (4.80 )

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
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, fair value of common stock prior to the closing of the Company’s IPO, valuation of share-based awards and the fair value of warrants prior to the conversion into warrants for the purchase of common stock upon the closing of the IPO. Actual results could differ from those estimates. The Company utilized significant estimates and assumptions in determining the fair value of its common stock prior to the Company’s IPO. The Company utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation
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, 2018 and 2017. The Company recognized other comprehensive loss of $2,000 for the year ended December 31, 2016 related to unrealized loss on available-for-sale investments.
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 market value. Cash and cash equivalents consist of the following at December 31, 2018 and 2017 (in thousands): December 31, 2018 2017 Cash and cash equivalents: Cash $ 228 $ 749 Money market funds 61,415 93,745 $ 61,643 $ 94,494
Investments	Investments The Company invests available cash primarily in U.S. and foreign corporate debt securities and United States government treasury securities. 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, 2018 and 2017. 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, 2018, 2017 and 2016.
Warrants to Purchase Shares Subject to Redemption	Warrants to Purchase Shares Subject to Redemption Prior to the closing of the IPO, the Company accounted for warrant instruments that either conditionally or unconditionally obligate the issuer to transfer assets as liabilities regardless of the timing of the redemption feature or price, even though the underlying shares may be classified as equity. These warrants were subject to revaluation at each balance sheet date, and any changes in fair value were recorded as a component of other income (expense) in the statements of operations and comprehensive loss. Upon the closing of the IPO, the warrants met the criteria to be classified in stockholders’ equity and the fair value of the warrant liability as of the IPO date was reclassified to stockholders’ equity (deficit).
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 In the first quarter of 2017, the Company made an accounting policy election to recognize forfeitures as they occur upon adoption of guidance per ASU No. 2016-09, Compensation – Stock Compensation The Company expenses the fair value of its share-based compensation awards to employees on a straight-line basis over the requisite service period, which is generally the vesting period. Stock-based compensation awards to non-employees are adjusted through stock-based compensation expense at each reporting period end to reflect the current fair value of such awards and are expensed on a straight-line basis.
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, 2018 2017 2016 Numerator: Net loss $ (35,648 ) $ (21,650 ) $ (24,507 ) Accretion of convertible preferred stock — (58 ) (69 ) Net loss attributable to common stockholders $ (35,648 ) $ (21,708 ) $ (24,576 ) Denominator: Weighted-average common shares – basic and diluted 20,741,226 4,520,337 1,339,254 Net loss per share attributable to common stockholders –basic and diluted $ (1.72 ) $ (4.80 ) $ (18.35 ) 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, 2018 2017 2016 Series A convertible preferred stock — — 4,400,410 Series B convertible preferred stock — — 4,753,536 Series C convertible preferred stock — — 4,791,563 Warrants 9,040 9,040 43,265 Stock options 2,141,527 1,508,124 1,348,845 Total 2,150,567 1,517,164 15,337,619
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, 2018 and 2017, 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 August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash In May 2017, the FASB issued ASU No. 2017-09, Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606)
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements 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 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

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Cash and Cash Equivalents	Cash and cash equivalents consist of the following at December 31, 2018 and 2017 (in thousands): December 31, 2018 2017 Cash and cash equivalents: Cash $ 228 $ 749 Money market funds 61,415 93,745 $ 61,643 $ 94,494
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, 2018 2017 2016 Numerator: Net loss $ (35,648 ) $ (21,650 ) $ (24,507 ) Accretion of convertible preferred stock — (58 ) (69 ) Net loss attributable to common stockholders $ (35,648 ) $ (21,708 ) $ (24,576 ) Denominator: Weighted-average common shares – basic and diluted 20,741,226 4,520,337 1,339,254 Net loss per share attributable to common stockholders –basic and diluted $ (1.72 ) $ (4.80 ) $ (18.35 )
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, 2018 2017 2016 Series A convertible preferred stock — — 4,400,410 Series B convertible preferred stock — — 4,753,536 Series C convertible preferred stock — — 4,791,563 Warrants 9,040 9,040 43,265 Stock options 2,141,527 1,508,124 1,348,845 Total 2,150,567 1,517,164 15,337,619

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 and indicates the fair value hierarchy of the valuation inputs utilized to determine such fair value (in thousands): 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 $ — $ — Description December 31, 2017 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 $ 93,745 $ 93,745 $ — $ — Total assets $ 93,745 $ 93,745 $ — $ —
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, 2018
Property Plant And Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment includes the following at December 31, 2017 and 2016 (in thousands): December 31, 2018 2017 Property and equipment: Laboratory equipment $ 728 $ 263 Computer equipment 6 6 Software 39 39 773 308 Less: Accumulated depreciation (259 ) (181 ) Property and equipment, net $ 514 $ 127

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2018
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): December 31, 2018 2017 Payroll and employee-related expenses $ 1,690 $ 1,132 Third-party research and development expenses 1,514 135 Professional fees 299 420 Loan interest 46 40 IPO-related costs — 111 Other 76 111 Total accrued expenses $ 3,625 $ 1,949

Loan and Security Agreement (Ta

Loan and Security Agreement (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Summary of Minimum Aggregate Future Loan and Interest Payments	The minimum aggregate future loan and interest payments at December 31, 2018 are as follows (in thousands): Years Ending December 31, 2019 $ 550 2020 4,450 2021 4,229 2022 2,032 Total minimum payments 11,261 Less: Amount representing interest (1,261 ) Less: Discount (20 ) Less: Current portion — Loan payable, net of current portion $ 9,980

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017: December 31, 2018 December 31, 2017 Warrants 9,040 9,040 Stock options 4,262,341 3,538,345 Employee stock purchase plan 405,742 206,284 Total 4,677,123 3,753,669

Stock Incentive Plans (Tables)

Stock Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 2016 Research and development $ 584 $ 147 $ 68 General and administrative 1,465 370 183 Total $ 2,049 $ 517 $ 251
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, 2017 1,508,124 $ 1.89 7.9 $ 12,328 Granted 801,474 8.57 Exercised (106,879 ) 1.29 Cancelled (61,192 ) 5.73 Outstanding at December 31, 2018 2,141,527 $ 4.32 7.7 $ 4,959 Exercisable at December 31, 2018 1,163,352 $ 2.07 6.9 $ 4,115
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, 2018, 2017 and 2016: Years Ended December 31, 2018 2017 2016 Risk-free interest rate 2.3% – 3.1% 1.9% – 2.3% 1.3% – 1.7% Expected dividend yield —% —% —% Expected term (in years) 5.5 – 6.1 5.6 – 6.3 5.4 – 6.4 Expected volatility 81% 81% 77%

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 30,294 $ 21,190 Research and development credits 5,843 4,732 Licenses 21 24 Stock based compensation 369 70 Other 418 300 Total gross deferred tax asset 36,945 26,316 Less: Valuation allowance (36,945 ) (26,316 ) Net deferred tax asset $ — $ —
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: 2018 2017 2016 Income tax computed at federal statutory tax rate 21.0 % 34.0 % 34.0 % Permanent differences — % (1.9 )% (0.2 )% State taxes, net of federal benefit 6.2 % 4.8 % 5.1 % Research and development and other tax credits 3.1 % 5.0 % 6.1 % Stock based compensation (0.5 )% (0.5 )% (0.3 )% Federal rate change — % (42.7 )% — % Change in deferred tax asset valuation allowance (29.8 )% 1.3 % (44.7 )% — % — % — %

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Commitments for Operating Leases	The minimum aggregate future operating lease commitments at December 31, 2018 are as follows (in thousands): December 31, 2018 2019 $ 487 2020 539 2021 30 $ 1,056

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	The following table contains quarterly financial information for 2018 and 2017. The Company believes that the following information reflects all normal recurring adjustments necessary for the fair statement of the information for the periods presented. 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 ) 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Total (in thousands, except per share amounts) Total operating expenses $ 5,542 $ 4,475 $ 4,362 $ 6,571 $ 20,950 Loss from operations (5,542 ) (4,475 ) (4,362 ) (6,571 ) (20,950 ) Net loss (5,671 ) (4,632 ) (4,670 ) (6,677 ) (21,650 ) Net loss attributable to common stockholders - basic and diluted $ (4.24 ) $ (3.46 ) $ (3.49 ) $ (0.48 ) $ (4.80 )

Organization and Basis of Pre_2

Organization and Basis of Presentation - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ 117,605	$ 81,957
Cash and cash equivalents	$ 61,643	$ 94,494

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
Entity incorporated date	Dec. 31, 2014
Change in unrealized gain (loss) on available for sale investments		$ 2,000	$ (2,000)
Impairment losses	$ 0	$ 0	$ 0
Income tax positions recognized, minimum percentage	50.00%
Subsequent Event
Summary Of Significant Accounting Policies [Line Items]
Operating lease, right-of-use assets				$ 1,000,000
Operating lease, liabilities				$ 1,000,000
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, 2018	Dec. 31, 2017
Cash and cash equivalents:
Cash	$ 228	$ 749
Money market funds	61,415	93,745
Cash and Cash Equivalents, at Carrying Value	$ 61,643	$ 94,494

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Assets (Details)	12 Months Ended
	Dec. 31, 2018
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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net loss	$ (9,611)	$ (9,510)	$ (8,647)	$ (7,880)	$ (6,677)	$ (4,670)	$ (4,632)	$ (5,671)	$ (35,648)	$ (21,650)	$ (24,507)
Accretion of convertible preferred stock										(58)	(69)
Net loss attributable to common stockholders									$ (35,648)	$ (21,708)	$ (24,576)
Denominator:
Weighted-average common shares – basic and diluted									20,741,226	4,520,337	1,339,254
Net loss per share attributable to common stockholders — basic and diluted	$ (0.46)	$ (0.46)	$ (0.42)	$ (0.38)	$ (0.48)	$ (3.49)	$ (3.46)	$ (4.24)	$ (1.72)	$ (4.80)	$ (18.35)

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of loss per share	2,150,567	1,517,164	15,337,619
Series A Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of loss per share			4,400,410
Series B Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of loss per share			4,753,536
Series C Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of loss per share			4,791,563
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	43,265
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of loss per share	2,141,527	1,508,124	1,348,845

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	$ 61,415	$ 93,745
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets	61,415	93,745
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	61,415	93,745
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	$ 61,415	$ 93,745

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
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, 2018	Dec. 31, 2017
Property and equipment:
Property and equipment, gross	$ 773	$ 308
Less: Accumulated depreciation	(259)	(181)
Property and equipment, net	514	127
Laboratory Equipment
Property and equipment:
Property and equipment, gross	728	263
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Depreciation expense	$ 78,000	$ 73,000	$ 46,000

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Payroll and employee-related expenses	$ 1,690	$ 1,132
Third-party research and development expenses	1,514	135
Professional fees	299	420
Loan interest	46	40
IPO-related costs		111
Other	76	111
Total accrued expenses	$ 3,625	$ 1,949

Loan and Security Agreement - A

Loan and Security Agreement - Additional Information (Details) - USD ($)	Jun. 29, 2018	Dec. 31, 2016	May 31, 2016	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
Loan agreement, stated interest rate		4.00%	4.00%
Loan agreement, interest rate above prime rate		0.50%	0.50%
Principal payments due				2020-05
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, interest rate above prime rate	5.00%
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, term	48 months
Loan agreement, interest only payment period	18 months
Loan agreement, extended interest only payment period	6 months
Expiration of initial interest only period	Dec. 31, 2019
Loan agreement, number of monthly payments	30 months
Loan agreement, frequency of payments				monthly
Loan agreement, extended additional interest only payment period	6 months
Loan agreement, number of additional monthly payments	24 months
Aggregate gross proceeds for success fee to be paid	$ 25,000,000
Success fee if gross proceeds received before June 30, 2019	200,000
Success fee if gross proceeds received after June 30, 2019	300,000
Loan Agreement | PWB | Minimum
Debt Instrument [Line Items]
Gross proceeds from sale of equity securities or upfront cash payment	$ 50,000,000

Loan and Security Agreement - S

Loan and Security Agreement - Summary of Minimum Aggregate Future Loan and Interest Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
2,019	$ 550
2,020	4,450
2,021	4,229
2,022	2,032
Total minimum payments	11,261
Less: Amount representing interest	(1,261)
Less: Discount	(20)
Less: Current portion		$ (3,870)
Loan payable, net of current portion	$ 9,980	$ 5,516

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 01, 2017	Nov. 06, 2017	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
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
Initial Public Offering
Class of Stock [Line Items]
Common stock, shares issued and sold		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]
Common stock, shares issued and sold	16,969
Gross proceeds from issuance of common stock	$ 0.2

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Shares of Common Stock Reserved (Details) - shares	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Shares of common stock reserved for future issuances	4,677,123	3,753,669
Warrants
Class of Stock [Line Items]
Shares of common stock reserved for future issuances	9,040	9,040
Stock Options
Class of Stock [Line Items]
Shares of common stock reserved for future issuances	4,262,341	3,538,345
Employee Stock Purchase Plan
Class of Stock [Line Items]
Shares of common stock reserved for future issuances	405,742	206,284

Stock Incentive Plans - Additio

Stock Incentive Plans - Additional Information (Details) - USD ($)	Jan. 01, 2019	Jan. 01, 2018	Oct. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expense related to awards granted				$ 2,049,000	$ 517,000	$ 251,000
Total intrinsic value of options exercised				$ 1,200,000	$ 276,000	$ 21,000
Shares of common stock reserved for future issuances				4,677,123	3,753,669
Employees and Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average fair value of options granted				$ 6.21	$ 6.16	$ 1.13
Non-Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expense related to awards granted				$ 100,000	$ 65,000	$ 24,000
Number of stock options granted				0	0
Weighted-average fair value of options granted						$ 1.38
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock reserved for future issuances				4,262,341	3,538,345
Stock Options | Employees and Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expense related to awards granted				$ 1,900,000	$ 500,000	$ 200,000
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 and 2019, the shares available for grant under the 2017 Plan was automatically increased by 827,786 and 832,361 shares, respectively.
Percentage criteria for additional shares granted			4.00%
Additional shares available for grant		827,786
2017 Plan | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future grant				2,120,814
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	832,361
2017 And 2011 Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock options granted				801,474
Unrecognized stock-based compensation expense related to unvested employee stock options				$ 4,400,000
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. No shares were added to the ESPP on January 1, 2019.
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	405,742
Amount withheld from employees for purchase of common stock shares under plan				$ 35,000
Common stock shares available for purchase under plan				7,488
2017 Employee Stock Purchase Plan | Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional shares available for grant	0

Stock Incentive Plans - Summary

Stock Incentive Plans - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 2,049	$ 517	$ 251
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	584	147	68
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 1,465	$ 370	$ 183

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) - Stock Options - Employees and Directors	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	2.30%	1.90%	1.30%
Risk-free interest rate, maximum	3.10%	2.30%	1.70%
Expected volatility, minimum	81.00%	81.00%	77.00%
Expected volatility, maximum	89.00%	87.00%	84.00%
Minimum
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	5 years 4 months 24 days
Maximum
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	6 years 4 months 24 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, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Outstanding, Beginning balance	1,508,124
Shares, Granted	801,474
Shares, Exercised	(106,879)
Shares, Cancelled	(61,192)
Shares, Outstanding, Ending balance	2,141,527	1,508,124
Shares, Exercisable	1,163,352
Weighted-Average Exercise Price, Outstanding, Beginning balance	$ 1.89
Weighted-Average Exercise Price, Granted	8.57
Weighted-Average Exercise Price, Exercised	1.29
Weighted-Average Exercise Price, Cancelled	5.73
Weighted-Average Exercise Price, Outstanding, Ending balance	4.32	$ 1.89
Weighted-Average Exercise Price, Exercisable	$ 2.07
Weighted-Average Remaining Contractual Life (in years), Outstanding	7 years 8 months 12 days	7 years 10 months 24 days
Weighted-Average Remaining Contractual Life (in years), Exercisable	6 years 10 months 24 days
Aggregate Intrinsic Value, Outstanding	$ 4,959	$ 12,328
Aggregate Intrinsic Value, Exercisable	$ 4,115

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Federal statutory tax rate									21.00%	34.00%	34.00%
Reduction in deferred tax assets										$ 9,300,000
Net loss	$ (9,611,000)	$ (9,510,000)	$ (8,647,000)	$ (7,880,000)	$ (6,677,000)	$ (4,670,000)	$ (4,632,000)	$ (5,671,000)	$ (35,648,000)	(21,650,000)	$ (24,507,000)
Income tax benefit									0
Valuation allowance	36,945,000				26,316,000				36,945,000	26,316,000
Valuation allowances period increase (decrease)									10,600,000	(300,000)
Accrued interest and penalties related to uncertain tax positions	0				0				0	0
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	111,100,000				77,900,000				$ 111,100,000	77,900,000
Operating loss carryforwards expiration period									2,037
Federal | Research and Development
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	4,000,000				3,300,000				$ 4,000,000	3,300,000
Tax credit carryforward expiration period									2,038
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	110,300,000				76,500,000				$ 110,300,000	76,500,000
Operating loss carryforwards expiration period									2,038
State | Research and Development
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	$ 2,200,000				$ 1,900,000				$ 2,200,000	$ 1,900,000
Tax credit carryforward expiration period									2,033

Income Taxes - Summary of Defer

Income Taxes - Summary of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 30,294	$ 21,190
Research and development credits	5,843	4,732
Licenses	21	24
Stock based compensation	369	70
Other	418	300
Total gross deferred tax asset	36,945	26,316
Less: Valuation allowance	$ (36,945)	$ (26,316)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Taxes Computed at Statutory Federal Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory tax rate	21.00%	34.00%	34.00%
Permanent differences		(1.90%)	(0.20%)
State taxes, net of federal benefit	6.20%	4.80%	5.10%
Research and development and other tax credits	3.10%	5.00%	6.10%
Stock based compensation	(0.50%)	(0.50%)	(0.30%)
Federal rate change		(42.70%)
Change in deferred tax asset valuation allowance	(29.80%)	1.30%	(44.70%)

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - Third Rock Ventures LLP - Consulting and Management Services - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Related Party Transaction [Line Items]
Services received from related party	$ 2,000	$ 69,000
Due to related party	$ 0		$ 0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)

Jun. 01, 2017

Aug. 31, 2018USD ($)ft²

Mar. 31, 2018ft²

Dec. 31, 2017ft²

Feb. 28, 2017ft²

Oct. 31, 2016

Aug. 31, 2016ft²

Oct. 31, 2013USD ($)ft²

Aug. 31, 2011USD ($)ft²

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Operating Leased Assets [Line Items]

Operating lease expiration date

Oct. 31, 2017

Operating leases, rent expense, net | $

$ 500,000

$ 400,000

$ 200,000

Newton, MA

Operating Leased Assets [Line Items]

Rentable office space under operating lease

6,055

Base rent for office space | $

$ 100,000

Natick, MA

Operating Leased Assets [Line Items]

Rentable laboratory space under operating lease

3,170

Base rent for lab space | $

$ 59,000

Sudbury, MA

Operating Leased Assets [Line Items]

Rentable office space under operating lease

2,928

Rentable laboratory space under operating lease

4,636

5,133

3,890

Base rent for lab space | $

$ 200,000

Operating lease extended period

2021-02

2019-02

Operating lease expiration period

2017-08

Option to lease other, rentable laboratory space under operating lease

2,029

Lease Amendment One | Newton, MA

Operating Leased Assets [Line Items]

Operating lease extended period

2016-10

Operating lease extended term

1 year

Lease Amendment Two | Newton, MA

Operating Leased Assets [Line Items]

Rentable office space under operating lease

7,795

Operating lease extended period

2018-05

Operating lease effective removal period

Jun. 1, 2017

Operating lease amendment period

2017-12

Operating lease expiration date

Dec. 31, 2020

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Commitments for Operating Leases (Details) $ in Thousands	Dec. 31, 2018USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2,019	$ 487
2,020	539
2,021	30
Total future operating lease commitment	$ 1,056

License Agreement - Additional

License Agreement - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018USD ($)shares
License Agreement [Line Items]
Type of Cost, Good or Service [Extensible List]	us-gaap:LicenseMember
Althea Technologies, Inc
License Agreement [Line Items]
Contract termination period	60 days
Althea Technologies, Inc | Maximum | License Agreement
License Agreement [Line Items]
Potential milestone payable	$ 56,000,000
Patents | Althea Technologies, Inc | License Agreement
License Agreement [Line Items]
Fees and costs incurred	$ 100,000
Issuance of common stock, net of issuance costs, shares | shares	88,186

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Details)	Jan. 01, 2019	Dec. 31, 2018
Defined Contribution Plan Disclosure [Line Items]
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.
Subsequent Event
Defined Contribution Plan Disclosure [Line Items]
Employer contribution percentage	100.00%
Employer matching contribution, percent of employees' salary	4.00%

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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Total operating expenses	$ 9,780	$ 9,705	$ 8,135	$ 7,973	$ 6,571	$ 4,362	$ 4,475	$ 5,542	$ 35,593	$ 20,950	$ 24,186
Loss from operations	(9,780)	(9,705)	(8,135)	(7,973)	(6,571)	(4,362)	(4,475)	(5,542)	(35,593)	(20,950)
Net loss	$ (9,611)	$ (9,510)	$ (8,647)	$ (7,880)	$ (6,677)	$ (4,670)	$ (4,632)	$ (5,671)	$ (35,648)	$ (21,650)	$ (24,507)
Net loss attributable to common stockholders - basic and diluted	$ (0.46)	$ (0.46)	$ (0.42)	$ (0.38)	$ (0.48)	$ (3.49)	$ (3.46)	$ (4.24)	$ (1.72)	$ (4.80)	$ (18.35)