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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2019	Aug. 05, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	ALRN
Entity Registrant Name	Aileron Therapeutics Inc
Entity Central Index Key	0001420565
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		27,810,358
Entity File Number	001-38130
Entity Tax Identification Number	134196017
Entity Address, Address Line One	490 Arsenal Way
Entity Address, Address Line Two	Suite 210
Entity Address, City or Town	Watertown
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02472
City Area Code	617
Local Phone Number	995-0900
Entity Shell Company	false
Entity Current Reporting Status	Yes

Condensed Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 10,157	$ 10,635
Investments	21,365	10,060
Prepaid expenses and other current assets	1,012	1,055
Restricted cash	25	25
Total current assets	32,559	21,775
Operating lease, right-of-use asset	6,385
Property and equipment, net	379	7,290
Restricted cash, non-current	568	568
Other assets	302	679
Total assets	40,193	30,312
Current liabilities:
Accrued expenses and other current liabilities	3,262	3,639
Accounts payable	1,719	1,731
Operating lease liabilities	406
Total current liabilities	5,387	5,370
Operating lease liabilities, net of current portion	4,822
Construction financing liability		5,342
Total liabilities	10,209	10,712
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized at June 30, 2019 and December 31, 2018, respectively; no shares issued and outstanding at June 30, 2019 and December 31, 2018
Common stock, $0.001 par value; 150,000,000 shares authorized at June 30, 2019 and December 31, 2018; 26,713,617 and 14,748,475 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively; 1,096,741 and 0 pre-funded warrants outstanding at June 30, 2019 and December 31, 2018	28	15
Additional paid-in capital	213,083	188,083
Accumulated other comprehensive loss	24	(5)
Accumulated deficit	(183,151)	(168,493)
Total stockholders’ equity	29,984	19,600
Total liabilities and stockholders’ equity	$ 40,193	$ 30,312

Condensed Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	26,713,617	14,748,475
Common stock, shares outstanding	26,713,617	14,748,475
Pre-funded Warrants [Member]
Warrants outstanding	1,096,741	0

Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development	4,304	5,320	8,478	10,166
General and administrative	3,075	4,339	6,214	7,256
Total operating expenses	7,379	9,659	14,692	17,422
Loss from operations	(7,379)	(9,659)	(14,692)	(17,422)
Interest income	207	168	307	343
Net loss	$ (7,172)	$ (9,491)	$ (14,385)	$ (17,079)
Net loss per share — basic and diluted	$ (0.26)	$ (0.64)	$ (0.68)	$ (1.16)
Weighted average common shares outstanding—basic and diluted	27,526,065	14,737,236	21,206,269	14,734,775
Comprehensive loss:
Net loss	$ (7,172)	$ (9,491)	$ (14,385)	$ (17,079)
Other comprehensive gain (loss):
Unrealized gain (loss) on investments, net of tax of $0	24	38	29	21
Total other comprehensive gain (loss)	24	38	29	21
Total comprehensive loss	$ (7,148)	$ (9,453)	$ (14,356)	$ (17,058)

Condensed Statement of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock and Common Warrants [Member]	Pre-funded Warrants and Common Warrants [Member]	Common Stock [Member]	Common Stock [Member] Common Stock and Common Warrants [Member]	Common Stock [Member] Pre-funded Warrants and Common Warrants [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Common Stock and Common Warrants [Member]	Additional Paid-in Capital [Member] Pre-funded Warrants and Common Warrants [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2017	$ 47,797			$ 15			$ 184,761			$ (33)	$ (136,946)
Beginning balance, shares at Dec. 31, 2017				14,723,818
Exercise of stock options	16						16
Exercise of stock options, shares				10,565
Stock-based compensation expense	767						767
Unrealized gain (loss) on investments	(17)									(17)
Net loss	(7,588)										(7,588)
Ending balance at Mar. 31, 2018	40,975			$ 15			185,544			(50)	(144,534)
Ending balance, shares at Mar. 31, 2018				14,734,383
Beginning balance at Dec. 31, 2017	47,797			$ 15			184,761			(33)	(136,946)
Beginning balance, shares at Dec. 31, 2017				14,723,818
Unrealized gain (loss) on investments	21
Net loss	(17,079)
Ending balance at Jun. 30, 2018	32,868			$ 15			186,890			(12)	(154,025)
Ending balance, shares at Jun. 30, 2018				14,737,402
Beginning balance at Mar. 31, 2018	40,975			$ 15			185,544			(50)	(144,534)
Beginning balance, shares at Mar. 31, 2018				14,734,383
Exercise of stock options	12						12
Exercise of stock options, shares				3,019
Stock-based compensation expense	1,334						1,334
Unrealized gain (loss) on investments	38									38
Net loss	(9,491)										(9,491)
Ending balance at Jun. 30, 2018	32,868			$ 15			186,890			(12)	(154,025)
Ending balance, shares at Jun. 30, 2018				14,737,402
Beginning balance at Dec. 31, 2018	$ 19,600			$ 15			188,083			(5)	(168,493)
Beginning balance, shares at Dec. 31, 2018	14,748,475			14,748,475
Exercise of stock options	$ 165						165
Exercise of stock options, shares				126,560
Stock-based compensation expense	563						563
Adoption of ASC 842, Leases \| ASU No. 2016-02 [Member]	(273)										(273)
Unrealized gain (loss) on investments	5									5
Net loss	(7,213)										(7,213)
Ending balance at Mar. 31, 2019	12,847			$ 15			188,811				(175,979)
Ending balance, shares at Mar. 31, 2019				14,875,035
Beginning balance at Dec. 31, 2018	$ 19,600			$ 15			188,083			(5)	(168,493)
Beginning balance, shares at Dec. 31, 2018	14,748,475			14,748,475
Exercise of stock options, shares	126,560
Unrealized gain (loss) on investments	$ 29
Net loss	(14,385)
Ending balance at Jun. 30, 2019	$ 29,984			$ 28			213,083			24	(183,151)
Ending balance, shares at Jun. 30, 2019	26,713,617			27,810,358
Beginning balance at Mar. 31, 2019	$ 12,847			$ 15			188,811				(175,979)
Beginning balance, shares at Mar. 31, 2019				14,875,035
Stock issued during period, value		$ 21,622	$ 2,203		$ 12	$ 1		$ 21,610	$ 2,202
Stock issued during period, shares					11,838,582	1,096,741
Stock-based compensation expense	460						460
Unrealized gain (loss) on investments	24									24
Net loss	(7,172)										(7,172)
Ending balance at Jun. 30, 2019	$ 29,984			$ 28			$ 213,083			$ 24	$ (183,151)
Ending balance, shares at Jun. 30, 2019	26,713,617			27,810,358

Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
Condensed Statements of Cash Flows - USD ($) $ in Thousands	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net loss	$ (14,385)	$ (17,079)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	58	82
Net amortization of premiums and discounts on investments	(94)	(93)
Stock-based compensation expense	1,023	2,101
Change in deferred rent		(11)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	29	141
Other assets	691	15
Accounts payable	(25)	(22)
Operating lease liabilities	(173)
Accrued expenses and other current liabilities	(317)	481
Net cash used in operating activities	(13,193)	(14,385)
Cash flows from investing activities:
Purchases of property and equipment	(131)	(213)
Purchases of investments	(21,284)	(20,763)
Proceeds from sales or maturities of investments	10,100	35,955
Net cash provided by (used in) investing activities	(11,315)	14,979
Cash flows from financing activities:
Proceeds from issuance of common stock, common warrants and pre-funded warrants, net of issuance costs	23,865
Proceeds from exercise of stock options	165	28
Net cash provided by financing activities	24,030	28
Net decrease in cash, cash equivalents and restricted cash	(478)	622
Cash, cash equivalents and restricted cash at beginning of period	11,228	11,951
Cash, cash equivalents and restricted cash at end of period	$ 10,750	$ 12,573

Nature of the Business and Basis of Presentation

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Nature of the Business and Basis of Presentation

1. Nature of the Business and Basis of Presentation

Aileron Therapeutics, Inc. (“Aileron” or the “Company”) is a clinical-stage biopharmaceutical company that is focused on developing and commercializing a novel class of stabilized cell-permeating alpha-helical peptides to address intracellular targets in oncology and other therapeutic areas. The Company’s lead product candidate, ALRN-6924, is a cell-permeating peptide that disrupts the interaction of p53 suppressors MDM2 and MDMX with tumor suppressor p53 to reactivate tumor suppression in non-mutant, or wild-type, p53 cancers. Based on preclinical data and preliminary evidence of safety and anti-tumor activity in the Company’s ongoing clinical trials, the Company believes that there may be a significant opportunity to develop ALRN-6924 in combination with other drugs for a wide variety of cancers. Additionally, preclinical experiments have shown that, in normal, non-cancer cells, ALRN-6924 induces cell cycle arrest when administered using a different schedule and lower doses than those used to induce cell death in cancer cells. Based on this preclinical data, the Company believes that a significant myelopreservation opportunity exists, to protect normal bone marrow cells against chemotherapy-induced toxicity.

The Company’s clinical development program for ALRN-6924 is currently focused on an ongoing Phase 2a expansion cohort studying the combination of ALRN-6924 and palbociclib (Ibrance™), marketed by Pfizer, Inc., for the treatment of MDM2-amplified advanced solid tumors and a planned Phase 1b/2 clinical trial to evaluate ALRN-6924 as a myelopreservative agent, to protect normal bone marrow cells against chemotherapy-induced toxicity.

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

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

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

Liquidity

In accordance with Accounting Standards Update (“ASU”) No. 2014-15, Disclosures of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), management must evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the company’s ability to continue as a going concern within one year after the date that the financial statements are issued. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Generally, to be considered probable of being effectively implemented, the plans must have been approved before the date that the financial statements are issued.

On April 2, 2019, the Company issued and sold in a private placement an aggregate of (i) 11,838,582 units, consisting of 11,838,582 shares of its common stock and associated warrants (the “common warrants”) to purchase an aggregate of 11,838,582 shares of common stock, for a combined price of $2.01 per unit and (ii) 1,096,741 units, consisting of (a) pre-funded warrants to purchase 1,096,741 shares of the Company’s common stock and (b) associated common warrants to purchase 1,096,741 shares of common stock, for a combined price of $2.01 per unit. The pre-funded warrants had an exercise price of $0.01 per share and had no expiration. The common warrants are exercisable at an exercise price of $2.00 per share and expire five years from the date of issuance.

The securities were sold pursuant to a securities purchase agreement entered into with accredited investors on March 28, 2019. The Company received aggregate gross proceeds from the private placement of approximately $26,000, before deducting placement agent fees and offering expenses of $2,175, and excluding the exercise of any warrants. In July 2019, all outstanding pre-funded warrants were exercised for 1,096,741 shares of common stock.

The Company’s interim financial statements have been prepared on a going concern basis, which contemplates the continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. Through June 30, 2019, the Company has funded its operations with net proceeds of $23,825 from its private placement on April 2, 2019, $50,009 from its initial public offering on July 5, 2017, $131,211 from sales of preferred stock, $552 from the exercise of stock options and $34,910 from a collaboration agreement. As of June 30, 2019, the Company had cash, cash equivalents and investments of $31,522. The Company has incurred losses and negative cash flows from operations and had an accumulated deficit of $183,151 as of June 30, 2019. The Company expects to continue to generate losses for the foreseeable future.

On July 12, 2019, the Company received a deficiency letter from the Listing Qualifications Department of the Nasdaq Stock Market notifying it that, for the last 30 consecutive business days, the bid price for the Company’s common stock had closed below the minimum $1.00 per share requirement for continued inclusion on the Nasdaq Global Market, referred to as the minimum bid price rule. In accordance with Nasdaq Listing Rules, the Company has an initial period of 180 calendar days, or until January 8, 2020, to regain compliance with the minimum bid price rule. The Company is actively monitoring its stock price and will consider any and all options available to the Company to maintain compliance. The alternatives to trading on the Nasdaq Capital Market or another national securities exchange are generally considered to be less efficient and less broad-based than the national securities exchanges and the liquidity of the Company’s common stock will likely be reduced if we fail to regain compliance with the minimum bid price rule.

As of August 6, 2019, the date of issuance of these unaudited interim condensed financial statements, the Company expects that its cash, cash equivalents and investments of $31,522 as of June 30, 2019, will be sufficient to fund its operating expenses and capital expenditure requirements into the fourth quarter of 2020. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations. Although the Company has been successful in raising capital in the past, there is no assurance that it will be successful in obtaining such additional financing on terms acceptable to the Company, if at all.

To execute its business plans, the Company will need substantial funding to support its continuing operations and pursue its growth strategy. Until such time as the Company can generate significant revenue from product sales, if ever, it expects to finance its operations through the sale of common stock in public offerings and/or private placements, debt financings or other capital sources, including collaborations with other companies or other strategic transactions. The Company may not be able to obtain financing on acceptable terms or at all. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion plans or commercialization efforts, which could adversely affect its business prospects.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of Estimates

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

Unaudited Interim Financial Information

The accompanying unaudited condensed financial statements as of June 30, 2019 and for the six months ended June 30, 2019 and 2018 have been prepared by the Company, pursuant to the rules and regulations of the SEC for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 that was filed with the SEC on March 29, 2019.

The unaudited interim condensed financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of June 30, 2019, the results of its operations for the three and six months ended June 30, 2019 and 2018 and its cash flows for the six months ended June 30, 2019 and 2018. The financial data and other information disclosed in these notes related to the three and six months ended June 30, 2019 and 2018 are unaudited. The results for the six months ended June 30, 2019 are not necessarily indicative of results to be expected for the year ending December 31, 2019, any other interim periods, or any future year or period. The accompanying balance sheet as of December 31, 2018 has been derived from the Company’s audited financial statements for the year ended December 31, 2018 previously filed with the SEC.

Cash Equivalents

The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market accounts, corporate notes and commercial paper, are stated at fair value.

Restricted Cash

As of June 30, 2019 and December 31, 2018, current restricted cash consisted of $25 of cash deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards. As of June 30, 2019 and December 31, 2018, non-current restricted cash consisted of $568 of cash deposited in a separate restricted bank account as a security deposit for the lease of the Company’s facility (see Note 8).

Investments

The Company classifies its available-for-sale debt security investments as current assets on the balance sheet if they mature within one year from the balance sheet date.

The Company classifies all of its investments as available-for-sale securities. The Company’s investments are measured and reported at fair value using quoted prices in active markets for similar securities or using other inputs that are observable or can be corroborated by observable market data. Unrealized gains and losses on available-for-sale securities are reported as accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity (deficit). The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the statements of operations and comprehensive loss.

The Company evaluates its 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 statements of operations and comprehensive loss. No such adjustments were necessary during the periods presented.

Fair Value Measurements

Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable.

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

•

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The Company’s cash equivalents and investments are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair value due to the short-term nature of these liabilities.

Net Loss per Share

The Company follows the two-class method when computing net loss per share as the Company has issued shares that meet the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed.

Basic net loss per share is computed by dividing the net loss by the weighted average number of shares of common stock and pre-funded warrants outstanding for the period. Diluted net income (loss) is computed by adjusting income (loss) per share to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share is computed by dividing the diluted net income (loss) by the weighted average number of shares of common stock outstanding for the period, including potential dilutive common shares. For purpose of this calculation, outstanding options to purchase common stock are considered potential dilutive common shares.

Recently Adopted Accounting Pronouncements

The Financial Accounting Standards Board (the “FASB”) issued ASU No. 2016-02, Leases (“ASU 2016-02”), to enhance the transparency and comparability of financial reporting related to leasing arrangements. Under this new lease standard, leases are required to be recognized on the balance sheet as right-of-use assets and operating lease liabilities. Disclosure requirements have been enhanced with the objective of enabling financial statement users to assess the amount, timing, and uncertainty of cash flows arising from leases.

The Company adopted the standard effective January 1, 2019. It has implemented the standard using the required modified retrospective approach and has also elected to utilize the package of practical expedients. The expedients used by the Company are as follows: (1) allowing an entity to not reassess the lease classification for any expired or existing leases, (2) allowing an entity to not reassess the treatment of initial direct costs as they related to existing leases, and (3) allowing an entity to not reassess whether expired or existing contracts are or contain leases. The Company elected to adopt the standard at the beginning of the period of adoption.

As a result of the adoption of ASU 2016-02, the Company de-recognized $7,079 of the building asset and $81 of accumulated depreciation related to its corporate headquarters at 490 Arsenal Way. Prior to the adoption of ASU 2016-02, the Company classified leasehold improvements associated with the 490 Arsenal Way building as building. Subsequent to the adoption of ASU 2016-02, the leasehold improvements associated with the 490 Arsenal Way building are classified as leasehold improvements.

	January 1, 2019 prior to ASC 842 Adoption			ASC 842 Adjustment			January 1, 2019 as adjusted
Operating lease right-of-use assets, net	$	—		$	6,697		$	6,697
Property and equipment, net		7,290			(6,998	)		292
Construction financing liability		5,342			(5,342	)		-
Other liabilities, current		3,639			(87	)		3,552
Operating lease liabilities, current		—			334			334
Operating lease liabilities, net of current portion		—			5,067			5,067
Accumulated deficit		(168,493	)		(273	)		(168,766	)

Recently Issued Accounting Pronouncements

The Company does not expect any accounting standards that have been issued or proposed by the FASB or other standards setting bodies that would require adoption on a future date to have a material impact on the Company’s financial statements upon adoption.

Fair Value of Financial Assets

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets

3. Fair Value of Financial Assets

The following tables present information about the Company’s assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values:

	Fair Value Measurements as of June 30, 2019 using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	5,669	$	—	$	—	$	5,669
Commercial paper		—		3,347		—		3,347
Investments:
Corporate notes		—		13,697		—		13,697
Commercial paper		—		7,668		—		7,668
	$	5,669	$	24,712	$	—	$	30,381

	Fair Value Measurements as of December 31, 2018 using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	6,041	$	—	$	—	$	6,041
Corporate notes		—		998		—		998
Commercial paper		—		2,495		—		2,495
Investments:
Corporate notes		—		3,644		—		3,644
Commercial paper		—		6,416		—		6,416
	$	6,041	$	13,553	$	—	$	19,594

As of June 30, 2019 and December 31, 2018, the Company’s cash equivalents and investments were invested in money market funds, corporate notes and commercial paper and were valued based on Level 1 and Level 2 inputs. In determining the fair value of its corporate notes and commercial paper at each date presented above, the Company relied on quoted prices for similar securities in active markets or using other inputs that are observable or can be corroborated by observable market data. The Company’s cash equivalents have original maturities of less than 90 days from the date of purchase. All available-for-sale investments have contractual maturities of less than one year. During the six months ended June 30, 2019 and the year ended December 31, 2018, there were no transfers between Level 1, Level 2 and Level 3.

- Definition

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

+ References + Details

Investments

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Investments

4. Investments

As of June 30, 2019 and December 31, 2018, the fair value of available-for-sale investments by type of security was as follows:

	June 30, 2019
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
Investments:
Corporate notes	$	13,684	$	13	$	—	$	13,697
Commercial paper		7,657		11		—		7,668
	$	21,341	$	24	$	—	$	21,365

	December 31, 2018
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Corporate notes	$	3,647	$	—	$	(3	)	$	3,644
Commercial paper		6,418		—		(2	)		6,416
	$	10,065	$	—	$	(5	)	$	10,060

Stock-Based Awards

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Awards

7. Stock-Based Awards

2017 Stock Incentive Plan

The Company’s 2017 Stock Incentive Plan (the “2017 Plan”) was approved by the Company’s stockholders on June 16, 2017 and became effective on June 28, 2017. Under the 2017 Plan, the Company may grant incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, awards of restricted stock units and other stock-based awards. The Company’s employees, officers, directors, consultants and advisors are eligible to receive awards under the 2017 Plan; however, incentive stock options may only be granted to employees. The 2017 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The number of shares of common stock covered by options and the date those options become exercisable, type of options to be granted, exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or its committee if so delegated.

Stock options granted under the 2017 Plan with service-based vesting conditions generally vest over four years and may not have a duration in excess of ten years, although options have been granted with vesting terms of less than four years.

The total number of shares of common stock that may be issued under the 2017 Plan was 3,248,607 as of June 30, 2019, of which 64,486 shares remained available for grant. The Company initially reserved 1,244,816 shares of common stock plus the number of shares equal to the sum of the number of shares of common stock then available for issuance under the 2016 plan, which was 424,601 shares, and the number of shares of common stock subject to outstanding awards under the 2006 plan and the 2016 plan that expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by us at their original issuance price pursuant to a contractual repurchase right. The number of shares of common stock that may be issued under the 2017 Plan will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2018 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the least of (i) 1,244,816 shares, (ii) 4% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors. On January 1, 2018 and January 1, 2019, the number of shares issuable under the 2017 Plan automatically increased by 588,953 shares and 589,939 shares, respectively.

During the six months ended June 30, 2019, pursuant to the terms of the 2017 Plan, the Company granted (i) options to employees and directors to purchase 1,692,150 shares of common stock at a weighted average exercise price of $1.63 per share and (ii) 50,000 restricted stock units with a weighted average grant date fair value of $1.75 that vest upon the satisfaction of specified performance milestones.

Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards.

The exercise price for stock options granted may not be less than the fair market value of the common stock as of the date of grant.

2017 Employee Stock Purchase Plan

On June 16, 2017, the Company’s stockholders approved the 2017 Employee Stock Purchase Plan (the “2017 ESPP”), which became effective on June 28, 2017. A total of 150,000 shares of common stock were initially reserved for issuance under this plan. The number of shares of common stock that may be issued under the 2017 ESPP will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2018 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the least of (i) 622,408 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors. On December 13, 2018, the Company’s compensation committee of the board of directors determined that the number of shares of common stock that may be issued under the 2017 ESPP would not be increased on January 1, 2018 or January 1, 2019.

2016 Stock Incentive Plan

The Company’s 2016 Stock Incentive Plan (the “2016 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. The 2016 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated.

Stock options granted under the 2016 Plan with service-based vesting conditions vest over four years and expire after ten years.

As of the effective date of the 2017 Plan, the board of directors determined to grant no further awards under the 2016 Plan. No stock options or other awards have been made under the 2016 Plan since the adoption of the 2017 Plan.

Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards under the 2017 Plan. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards under the 2017 Plan.

2006 Stock Incentive Plan

The Company’s 2006 Stock Incentive Plan, as amended, (the “2006 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. The 2006 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated.

Stock options granted under the 2006 Plan with service-based vesting conditions generally vest over four years and expire after ten years, although options have been granted with vesting terms of less than four years.

The 2006 Plan expired in 2016. Since its expiration No further awards have been made under the 2006 Plan.

Stock Option Valuation

The assumptions that the Company used to determine the grant-date fair value of the stock options granted to employees and directors during the six months ended June 30, 2019 and 2018 were as follows, presented on a weighted average basis:

	Six Months Ended June 30, 2019			Six Months Ended June 30, 2018
Risk-free interest rate		2.35	%		2.75	%
Expected term (in years)		6.3			6.2
Expected volatility		76.0	%		76.0	%
Expected dividend yield		0	%		0	%

Stock Options

The following table summarizes the Company’s stock option activity since January 1, 2019:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding at December 31, 2018		2,528,297		$	6.31		6.7	$	—
Granted		1,692,150			1.63
Exercised		(126,560	)		1.30
Canceled		(66,540	)		3.52
Forfeited		(149,879	)		7.26
Outstanding at June 30, 2019		3,877,468		$	4.44		7.9	$	—
Options exercisable at June 30, 2019		1,299,550		$	6.80		4.8	$	—
Options vested and expected to vest at June 30, 2019		3,784,829		$	6.80		4.8	$	—
Options exercisable at December 31, 2018		1,214,016		$	6.29		3.9	$	—
Options vested and expected to vest at December 31, 2018		2,485,495		$	6.31		6.6	$	—

The weighted average grant-date fair value of stock options granted during the six months ended June 30, 2019 and 2018 was $1.11 and $4.79, respectively.

The aggregate fair value of stock options that vested during the six months ended June 30, 2019 and 2018 was $1,142 and $1,812, respectively.

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of stock options exercised during the six months ended June 30, 2019 and 2018 was $109 and $93, respectively.

Restricted Stock Units

On April 15, 2019, the Company granted restricted stock units under the 2017 Stock Incentive Plan. The following table summarizes the Company’s restricted stock unit activity during the six months ended June 30, 2019:

			Weighted-Average
			Grant Date
	Units		per Unit
Outstanding, non-vested at December 31, 2018		-		-
Issued		50,000	$	1.75
Vested		-		-
Canceled/forfeited		-		-
Outstanding, non-vested at June 30, 2019		50,000	$	1.75

Stock-Based Compensation

The Company recorded stock-based compensation expense related to stock options and restricted stock units in the following expense categories of its statements of operations and comprehensive loss:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development expenses	$	112	$	240	$	193	$	510
General and administrative expenses		348		1,094		830		1,591
	$	460	$	1,334	$	1,023	$	2,101

During the three and six months ended June 30, 2019 the Company recognized stock-based compensation expense of $23 and $23, respectively, included in the table above, related to performance-based awards for which achievement of such performance-based conditions were deemed probable.

The Company used an estimated forfeiture rate of 2.43% to calculate its stock compensation expense for each of the six months ended June 30, 2019 and 2018.

As of June 30, 2019, the Company had an aggregate of $5,449 of unrecognized stock-based compensation expense, which it expects to recognize over a weighted average period of 2.5 years.

Net Loss per Share

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Net Loss per Share

8. Net Loss per Share

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

	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Numerator:
Net loss	$	(7,172	)	$	(9,491	)	$	(14,385	)	$	(17,079	)

Denominator:
Weighted average common shares outstanding—basic and diluted.		26,453,428			14,737,236			20,666,988			14,734,775
Weighted average pre-funded warrants to purchase common stock.		1,072,637			-			539,281			-
Total		27,526,065			14,737,236			21,206,269			14,734,775

Net loss per share —basic and diluted	$	(0.26	)	$	(0.64	)	$	(0.68	)	$	(1.16	)

The Company’s potential dilutive securities, which include stock options and warrants, have been excluded from the computation of diluted net loss per share whenever the effect of including them would be to reduce the net loss per share. In periods where there is a net loss, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share is the same. The following potential shares of common stock, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect:

	Six Months Ended June 30,
	2019		2018
Stock options to purchase common stock		3,877,468		2,037,762
Warrants to purchase common stock		12,935,323		-
Restricted stock units to purchase common stock		50,000		-
Total		16,862,791		2,037,762

Commitments and Contingencies

6 Months Ended

Jun. 30, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

9. Commitments and Contingencies

Operating Lease

490 Arsenal Way

On April 4, 2018, the Company entered into a lease agreement for office and laboratory space located in a building (the “Building”) at 490 Arsenal Way, Watertown, Massachusetts (the “490 Arsenal Way Lease”), which is now the Company’s corporate headquarters. Under the terms of the 490 Arsenal Way Lease, starting on August 21, 2018, the Company leases approximately 18,768 square feet of office and laboratory space at $52.55 per square foot per year, or $986 per year in base rent, which is subject to scheduled annual rent increases plus certain operating expenses and taxes. The Company currently maintains a $568 security deposit related to the 490 Arsenal Way Lease. Pursuant to the 490 Arsenal Way Lease, the landlord contributed an aggregate of $2,419 toward the cost of construction and tenant improvements for the Building.

The Company has occupied the Building beginning on August 21, 2018 and the 490 Arsenal Way Lease will continue until August 31, 2026. The Company has the option to extend the 490 Arsenal Way Lease for one five-year terms. The Company is accounting for this lease under ASC 842 using its initial eight-year term through August 31, 2026 and will reassess the lease term on a quarterly basis.

Due to the Company’s involvement in the construction project, including having responsibility to pay for a portion of the costs of finish work and mechanical, electrical, and plumbing elements of the Building, among other items, the Company was deemed for accounting purposes to be the owner of the Building during the construction period, per ASC 840. Accordingly, under ASC 840, construction costs that were incurred by the landlord directly or indirectly through reimbursement to the Company as part of its tenant improvement allowance were recorded as an asset in Property, plant and equipment, net on the Company’s consolidated balance sheets.

The Company evaluated the 490 Arsenal Way Lease upon occupancy on August 21, 2018 and determined that the 490 Arsenal Way Lease did not meet the criteria for “sale-leaseback” treatment under ASC 840. This determination was based on, among other things, the Company's continuing involvement with the property in the form of non-recourse financing to the lessor. Accordingly, upon occupancy, the Company commenced depreciating the portion of the building in service over a useful life of 30 years and incurred interest expense related to the financing obligation.

As part of its adoption of ASC 842, the Company de-recognized the building asset and corresponding financing obligation recorded on the Company’s consolidated balance sheets as of January 1, 2019, in accordance with the ASC 842 transition guidance. In applying the ASC 842 transition guidance, the Company classified this lease as an operating lease and recorded a right-of-use asset of $6,697 and lease liability of $5,401 on the effective date. The Company is recognizing rent expense on a straight-line basis throughout the remaining term of the lease.

Summary of all lease costs recognized under ASC 842

The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the six months ended June 30, 2019:

	Three Months Ended June 30, 2019			Six Months Ended June 30, 2019
Lease cost (1)
Operating lease cost	$	317		$	634
Total lease cost	$	317		$	634

Other Information
Operating cash flows used for operating leases	$	246		$	493
Weighted average remaining lease term (in years)		7.2			7.2
Weighted average discount rate		12.0	%		12.0	%

(1)

Short-term lease costs and variable lease costs incurred by the Company for the six months ended June 30, 2019 were immaterial.

As of June 30, 2019, future minimum commitments under ASC 842 under the Company’s operating leases were as follows:

	As of June 30, 2019
2019 (excluding the six months ended June 30, 2019)	$	504
2020		1,026
2021		1,058
2022		1,089
2023		1,122
2024 and thereafter		3,126
Total lease payments		7,925
Less: imputed interest		(2,697	)
Total operating lease liabilities	$	5,228

As of December 31, 2018, future minimum commitments under ASC 840 under the Company’s operating leases were as follows:

	As of December 31, 2018
2019	$	997
2020		1,026
2021		1,058
2022		1,089
2023		1,122
2024 and thereafter		3,126
Total lease payments		8,418

Intellectual Property Licenses

Harvard and Dana-Farber Agreement

In August 2006, the Company entered into an exclusive license agreement with President and Fellows of Harvard College (“Harvard”) and Dana-Farber Cancer Institute (“DFCI”). The agreement granted the Company an exclusive worldwide license, with the right to sublicense, under specified patents and patent applications to develop, obtain regulatory approval for and commercialize specified product candidates based on cell-permeating peptides. Under the agreement, the Company is obligated to use commercially reasonable efforts to develop and commercialize one or more licensed products and to achieve specified milestone events by specified dates. In connection with entering into the agreement, the Company paid an upfront license fee and issued to Harvard and DFCI shares of its common stock.

In February 2010, the agreement was amended and restated (the “Harvard/DFCI agreement”) under which additional patent rights were added to the scope of the license agreement and the annual license maintenance fees were increased. Under the Harvard/DFCI agreement, the Company is obligated to make aggregate milestones payments of up to $7,700 per licensed therapeutic product upon the Company’s achievement of specified clinical, regulatory and sales milestones with respect to such product and up to $700 per licensed diagnostic product upon the Company’s achievement of specified regulatory and sales milestones with respect to such product. In addition, the Company is obligated to pay royalties of low single-digit percentages on annual net sales of licensed products sold by the Company, its affiliates or its sublicensees. The royalties are payable on a product-by-product and country-by-country basis, and may be reduced in specified circumstances. In addition, the agreement obligates the Company to pay a percentage, up to the mid-twenties, of fees received by the Company in connection with its sublicense of the licensed products. In accordance with the terms of the agreement, the Company’s sublicense payment obligations may be subject to specified reductions.

The Harvard/DFCI agreement requires the Company to pay annual license maintenance fees of $145 each year. Any payments made in connection with the annual license maintenance fees will be credited against any royalties due.

The Company incurred license fees of $145 during each of the six months ended June 30, 2019 and 2018. In addition, the Company did not make any milestone payments during the three and six months ended June 30, 2019 and 2018. As of June 30, 2019, no additional milestones had been achieved and no liabilities for additional milestone payments had been recorded in the Company’s financial statements. Through June 30, 2019 and December 31, 2018, the Company had made non-refundable cash payments, consisting of license and maintenance fees, milestone payments and sublicense fees, totaling $4,718 and $4,573, respectively.

As of June 30, 2019, the Company had not developed a commercial product using the licensed technologies and no royalties under the agreement had been paid or were due.

Under the Harvard/DFCI agreement, the Company is responsible for all patent expenses related to the prosecution and maintenance of the licensed patents and applications in-licensed under the agreement as well as cost reimbursement of amounts incurred for all documented patent-related expenses. The agreement will expire on a product-by-product and country-by-country basis upon the last to expire of any valid patent claim pertaining to licensed products covered under the agreement.

Umicore Agreement

In December 2006, the Company entered into a license agreement with Materia, Inc. (“Materia”), under which it was granted a non-exclusive worldwide license, with the right to sublicense, under specified patent and patent applications to utilize Materia’s catalysts to develop, obtain regulatory approval for and commercialize specified peptides owned or controlled by Materia and the right to manufacture specified compositions owned or controlled by Materia. In February 2017, Materia assigned the license agreement (the “Umicore agreement”) to Umicore Precious Metals Chemistry USA, LLC (“Umicore”), and Umicore agreed to continue to supply the Company under the agreement.

Under the Umicore agreement, the Company is obligated to make aggregate milestone payments to Umicore of up to $6,400 upon the Company’s achievement of specified clinical, regulatory and sales milestones with respect to each licensed product. In addition, the Company is obligated to pay tiered royalties ranging in the low single-digit percentages on annual net sales of licensed products sold by the Company or its sublicensees. The royalties are payable on a product-by-product and country-by-country basis and may be reduced in specified circumstances.

The Umicore agreement requires the Company to pay annual license fees of $50. The Company incurred license fees of $50 during the six months ended June 30, 2019 and did not incur any license fees during the six months ended June 30, 2018. In addition, the Company did not make any milestone payments during the three and six months ended June 30, 2019 and 2018. As of June 30, 2019, no additional milestones had been achieved and no liabilities for additional milestone payments had been recorded in the Company’s financial statements.

The agreement expires upon the expiration of the Company’s obligation to pay royalties in each territory covered under the agreement.

Scripps Agreement

In October 2010, the Company entered into a patent license agreement (the “Scripps agreement”) with The Scripps Research Institute (“Scripps”) under which it was granted a license, with the right to sublicense, for the exclusive worldwide rights to utilize Scripps’ “Click” chemistry for therapeutics and non-exclusive worldwide rights for diagnostics with the Company’s stabilized peptide and protein technology platforms.

Under the agreement, the Company is obligated to make aggregate milestone payments to Scripps of up to $1,900 for each licensed peptide product and up to $950 for each licensed protein product upon achieving of specified clinical, regulatory and commercial milestones. In addition, the Company is obligated to pay tiered royalties ranging in the low single-digit percentages on annual net sales of licensed products sold by the Company or its sublicensees. The royalties are payable on a product-by-product and country-by-country basis. The Scripps agreement requires the Company to pay annual license fees of $50. The Company did not incur any license fees during the three and six months ended June 30, 2019 and 2018, respectively.

As of June 30, 2019, no milestones had been achieved and no liabilities for milestone payments had been recorded in the Company’s financial statements. As of June 30, 2019, the Company had not developed a commercial product using the licensed technologies and no royalties under the agreement had been paid or were due.

The agreement expires upon expiration of the last of any patent rights covered under the agreement.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it had not accrued any liabilities related to such obligations in its financial statements as of June 30, 2019 or December 31, 2018.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Use of Estimates

Unaudited Interim Financial Information

Cash Equivalents

Restricted Cash

Investments

The Company classifies its available-for-sale debt security investments as current assets on the balance sheet if they mature within one year from the balance sheet date.

Fair Value Measurements

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Net Loss per Share

Recently Adopted Accounting Pronouncements

	January 1, 2019 prior to ASC 842 Adoption			ASC 842 Adjustment			January 1, 2019 as adjusted
Operating lease right-of-use assets, net	$	—		$	6,697		$	6,697
Property and equipment, net		7,290			(6,998	)		292
Construction financing liability		5,342			(5,342	)		-
Other liabilities, current		3,639			(87	)		3,552
Operating lease liabilities, current		—			334			334
Operating lease liabilities, net of current portion		—			5,067			5,067
Accumulated deficit		(168,493	)		(273	)		(168,766	)

Recently Issued Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2019

ASU No. 2016-02 [Member]

Schedule of Impact of Adoption of ASC 842

	January 1, 2019 prior to ASC 842 Adoption			ASC 842 Adjustment			January 1, 2019 as adjusted
Operating lease right-of-use assets, net	$	—		$	6,697		$	6,697
Property and equipment, net		7,290			(6,998	)		292
Construction financing liability		5,342			(5,342	)		-
Other liabilities, current		3,639			(87	)		3,552
Operating lease liabilities, current		—			334			334
Operating lease liabilities, net of current portion		—			5,067			5,067
Accumulated deficit		(168,493	)		(273	)		(168,766	)

Fair Value of Financial Assets (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Summary of Assets Measured at Fair Value on Recurring Basis

	Fair Value Measurements as of June 30, 2019 using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	5,669	$	—	$	—	$	5,669
Commercial paper		—		3,347		—		3,347
Investments:
Corporate notes		—		13,697		—		13,697
Commercial paper		—		7,668		—		7,668
	$	5,669	$	24,712	$	—	$	30,381

	Fair Value Measurements as of December 31, 2018 using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	6,041	$	—	$	—	$	6,041
Corporate notes		—		998		—		998
Commercial paper		—		2,495		—		2,495
Investments:
Corporate notes		—		3,644		—		3,644
Commercial paper		—		6,416		—		6,416
	$	6,041	$	13,553	$	—	$	19,594

Investments (Tables)

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Summary of Fair Value of Available for Sale Investments

As of June 30, 2019 and December 31, 2018, the fair value of available-for-sale investments by type of security was as follows:

	June 30, 2019
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
Investments:
Corporate notes	$	13,684	$	13	$	—	$	13,697
Commercial paper		7,657		11		—		7,668
	$	21,341	$	24	$	—	$	21,365

	December 31, 2018
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Corporate notes	$	3,647	$	—	$	(3	)	$	3,644
Commercial paper		6,418		—		(2	)		6,416
	$	10,065	$	—	$	(5	)	$	10,060

Stock-Based Awards (Tables)

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Valuation Assumptions of Stock Options Granted

	Six Months Ended June 30, 2019			Six Months Ended June 30, 2018
Risk-free interest rate		2.35	%		2.75	%
Expected term (in years)		6.3			6.2
Expected volatility		76.0	%		76.0	%
Expected dividend yield		0	%		0	%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity since January 1, 2019:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding at December 31, 2018		2,528,297		$	6.31		6.7	$	—
Granted		1,692,150			1.63
Exercised		(126,560	)		1.30
Canceled		(66,540	)		3.52
Forfeited		(149,879	)		7.26
Outstanding at June 30, 2019		3,877,468		$	4.44		7.9	$	—
Options exercisable at June 30, 2019		1,299,550		$	6.80		4.8	$	—
Options vested and expected to vest at June 30, 2019		3,784,829		$	6.80		4.8	$	—
Options exercisable at December 31, 2018		1,214,016		$	6.29		3.9	$	—
Options vested and expected to vest at December 31, 2018		2,485,495		$	6.31		6.6	$	—

Summary of Restricted Stock Unit Activity

			Weighted-Average
			Grant Date
	Units		per Unit
Outstanding, non-vested at December 31, 2018		-		-
Issued		50,000	$	1.75
Vested		-		-
Canceled/forfeited		-		-
Outstanding, non-vested at June 30, 2019		50,000	$	1.75

Summary of Stock Based Compensation Expense

The Company recorded stock-based compensation expense related to stock options and restricted stock units in the following expense categories of its statements of operations and comprehensive loss:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development expenses	$	112	$	240	$	193	$	510
General and administrative expenses		348		1,094		830		1,591
	$	460	$	1,334	$	1,023	$	2,101

Net Loss per Share (Tables)

6 Months Ended

Jun. 30, 2019

Earnings Per Share [Abstract]

Basic and Diluted Net Loss per Share

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

	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Numerator:
Net loss	$	(7,172	)	$	(9,491	)	$	(14,385	)	$	(17,079	)

Denominator:
Weighted average common shares outstanding—basic and diluted.		26,453,428			14,737,236			20,666,988			14,734,775
Weighted average pre-funded warrants to purchase common stock.		1,072,637			-			539,281			-
Total		27,526,065			14,737,236			21,206,269			14,734,775

Net loss per share —basic and diluted	$	(0.26	)	$	(0.64	)	$	(0.68	)	$	(1.16	)

Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share

The following potential shares of common stock, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect:

	Six Months Ended June 30,
	2019		2018
Stock options to purchase common stock		3,877,468		2,037,762
Warrants to purchase common stock		12,935,323		-
Restricted stock units to purchase common stock		50,000		-
Total		16,862,791		2,037,762

Commitments and Contingencies (Tables)

6 Months Ended

Jun. 30, 2019

Commitments And Contingencies Disclosure [Abstract]

Summary of Lease Costs Recognized Under ASC 842 and Other Information Pertaining to Operating Leases

The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the six months ended June 30, 2019:

	Three Months Ended June 30, 2019			Six Months Ended June 30, 2019
Lease cost (1)
Operating lease cost	$	317		$	634
Total lease cost	$	317		$	634

Other Information
Operating cash flows used for operating leases	$	246		$	493
Weighted average remaining lease term (in years)		7.2			7.2
Weighted average discount rate		12.0	%		12.0	%

(1)

Short-term lease costs and variable lease costs incurred by the Company for the six months ended June 30, 2019 were immaterial.

Future Minimum Commitments Under ASC 842 Under Operating Leases

As of June 30, 2019, future minimum commitments under ASC 842 under the Company’s operating leases were as follows:

	As of June 30, 2019
2019 (excluding the six months ended June 30, 2019)	$	504
2020		1,026
2021		1,058
2022		1,089
2023		1,122
2024 and thereafter		3,126
Total lease payments		7,925
Less: imputed interest		(2,697	)
Total operating lease liabilities	$	5,228

Future Minimum Commitments Under ASC 840 Under Operating Leases

As of December 31, 2018, future minimum commitments under ASC 840 under the Company’s operating leases were as follows:

	As of December 31, 2018
2019	$	997
2020		1,026
2021		1,058
2022		1,089
2023		1,122
2024 and thereafter		3,126
Total lease payments		8,418

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands					6 Months Ended
	Jul. 12, 2019	Apr. 02, 2019	Mar. 28, 2019	Jul. 05, 2017	Jun. 30, 2019	Jul. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Proceeds from exercise of stock options					$ 552
Proceeds from collaboration agreement					34,910
Cash, cash equivalents and investments					31,522
Accumulated deficit					(183,151)		$ (168,493)
Net proceeds from issuance of private placement		$ 23,825
Subsequent Event [Member]
Class Of Stock [Line Items]
Stock market bidding requirements, description	On July 12, 2019, the Company received a deficiency letter from the Listing Qualifications Department of the Nasdaq Stock Market notifying it that, for the last 30 consecutive business days, the bid price for the Company’s common stock had closed below the minimum $1.00 per share requirement for continued inclusion on the Nasdaq Global Market, referred to as the minimum bid price rule. In accordance with Nasdaq Listing Rules, the Company has an initial period of 180 calendar days, or until January 8, 2020, to regain compliance with the minimum bid price rule. The Company is actively monitoring its stock price and will consider any and all options available to the Company to maintain compliance. The alternatives to trading on the Nasdaq Capital Market or another national securities exchange are generally considered to be less efficient and less broad-based than the national securities exchanges and the liquidity of the Company’s common stock will likely be reduced if we fail to regain compliance with the minimum bid price rule.
Minimum closing bid requirement, price per share	$ 1.00
Common Stock [Member]
Class Of Stock [Line Items]
Net proceeds from issuance of initial public offering				$ 50,009
Common Stock [Member] \| Subsequent Event [Member]
Class Of Stock [Line Items]
Pre-funded warrants, exercised						1,096,741
Preferred Stock [Member]
Class Of Stock [Line Items]
Proceeds from sales of stock					$ 131,211
Private Placement [Member]
Class Of Stock [Line Items]
Aggregate gross proceeds from private placement		26,000	$ 26,000
Placement agent fees		$ 2,175	$ 2,175
Private Placement [Member] \| Stock Units [Member] \| Purchase Agreement One [Member]
Class Of Stock [Line Items]
Issue and sale of aggregate shares		11,838,582
Sale of stock, combined price per unit		$ 2.01
Private Placement [Member] \| Stock Units [Member] \| Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Issue and sale of aggregate shares		1,096,741
Sale of stock, combined price per unit		$ 2.01
Private Placement [Member] \| Common Warrants [Member] \| Purchase Agreement One [Member]
Class Of Stock [Line Items]
Aggregate shares purchase for warrants		11,838,582
Warrants exercisable, exercise price		$ 2.00
Warrants and Rights Outstanding, Term		5 years
Private Placement [Member] \| Common Stock [Member] \| Purchase Agreement One [Member]
Class Of Stock [Line Items]
Stock repurchase program, number of shares to be purchased		11,838,582
Private Placement [Member] \| Common Stock [Member] \| Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Stock repurchase program, number of shares to be purchased		1,096,741
Private Placement [Member] \| Pre-funded Warrants [Member] \| Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Aggregate shares purchase for warrants		1,096,741
Warrants exercisable, exercise price		$ 0.01

Summary of Significant Accounting Policies - Schedule of Impact of Adoption of ASC 842 (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease right-of-use assets, net	$ 6,385
Property and equipment, net	379		$ 7,290
Construction financing liability			5,342
Operating lease liabilities, current	406
Operating lease liabilities, net of current portion	4,822
Accumulated deficit	$ (183,151)		(168,493)
Prior to ASC 842 Adoption [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Property and equipment, net			7,290
Construction financing liability			5,342
Other liabilities, current			3,639
Accumulated deficit			$ (168,493)
ASU No. 2016-02 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease right-of-use assets, net		$ 6,697
Property and equipment, net		292
Other liabilities, current		3,552
Operating lease liabilities, current		334
Operating lease liabilities, net of current portion		5,067
Accumulated deficit		(168,766)
ASU No. 2016-02 [Member] \| ASC 842 Adjustment [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease right-of-use assets, net		6,697
Property and equipment, net		(6,998)
Construction financing liability		(5,342)
Other liabilities, current		(87)
Operating lease liabilities, current		334
Operating lease liabilities, net of current portion		5,067
Accumulated deficit		$ (273)

Fair Value of Financial Assets - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	$ 21,365	$ 10,060
Corporate Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	13,697	3,644
Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	7,668	6,416
Recurring [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	30,381	19,594
Recurring [Member] \| Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	5,669	6,041
Recurring [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	24,712	13,553
Recurring [Member] \| Corporate Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	13,697	3,644
Recurring [Member] \| Corporate Notes [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	13,697	3,644
Recurring [Member] \| Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	7,668	6,416
Recurring [Member] \| Commercial Paper [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	7,668	6,416
Recurring [Member] \| Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	5,669	6,041
Recurring [Member] \| Money Market Funds [Member] \| Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	5,669	6,041
Recurring [Member] \| Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	3,347	2,495
Recurring [Member] \| Commercial Paper [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	$ 3,347	2,495
Recurring [Member] \| Corporate Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents		998
Recurring [Member] \| Corporate Notes [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents		$ 998

Stockholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Thousands			6 Months Ended
	Apr. 02, 2019 USD ($) $ / shares shares	Mar. 28, 2019 USD ($)	Jun. 30, 2019 USD ($) $ / shares
Class Of Stock [Line Items]
Grant date fair value of the common warrants, per share \| $ / shares			$ 1.78
Grant date fair value of the common warrants \| $			$ 23,025
Risk Free Rate [Member]
Class Of Stock [Line Items]
Warrants and rights, measurement input			2.23
Expected Term [Member]
Class Of Stock [Line Items]
Warrants and Rights Outstanding, Term			5 years
Volatility [Member]
Class Of Stock [Line Items]
Warrants and rights, measurement input			76
Private Placement [Member]
Class Of Stock [Line Items]
Aggregate gross proceeds from private placement \| $	$ 26,000	$ 26,000
Placement agent fees \| $	$ 2,175	$ 2,175
Private Placement [Member] \| Stock Units [Member] \| Purchase Agreement One [Member]
Class Of Stock [Line Items]
Issue and sale of aggregate shares	11,838,582
Sale of stock, combined price per unit \| $ / shares	$ 2.01
Private Placement [Member] \| Stock Units [Member] \| Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Issue and sale of aggregate shares	1,096,741
Sale of stock, combined price per unit \| $ / shares	$ 2.01
Private Placement [Member] \| Common Warrants [Member] \| Purchase Agreement One [Member]
Class Of Stock [Line Items]
Aggregate shares purchase for warrants	11,838,582
Warrants exercisable, exercise price \| $ / shares	$ 2.00
Warrants and Rights Outstanding, Term	5 years
Private Placement [Member] \| Common Stock [Member] \| Purchase Agreement One [Member]
Class Of Stock [Line Items]
Stock repurchase program, number of shares to be purchased	11,838,582
Private Placement [Member] \| Common Stock [Member] \| Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Stock repurchase program, number of shares to be purchased	1,096,741
Private Placement [Member] \| Pre-funded Warrants [Member] \| Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Aggregate shares purchase for warrants	1,096,741
Warrants exercisable, exercise price \| $ / shares	$ 0.01

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended			6 Months Ended
	Jan. 01, 2019	Jan. 01, 2018	Jun. 16, 2017	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted							1,692,150
Options granted, weighted average exercise price per share							$ 1.63
Weighted average grant-date fair value of stock options							$ 1.11	$ 4.79
Aggregate fair value of stock options vested							$ 1,142	$ 1,812
Aggregate intrinsic value of stock options exercised							$ 109	93
Share based compensation expense estimated forfeiture rate							2.43%
Aggregate unrecognized stock-based compensation expense				$ 5,449			$ 5,449
Unrecognized stock-based compensation expense, weighted average period expects for recognition							2 years 6 months
Recognized stock-based compensation expense				460		$ 1,334	$ 1,023	$ 2,101
Performance-based Awards [[Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized stock-based compensation expense				$ 23			$ 23
2017 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period							4 years
Number of shares, available for grant				3,248,607			3,248,607
Number of shares remained available for grant				64,486			64,486
Stock reserved for future issuance				1,244,816			1,244,816
Maximum annual increase in common stock reserved for future issuance							1,244,816
Percentage of common stock shares outstanding							4.00%
Increase to shares authorized for issuance	589,939	588,953
Options granted							1,692,150
Options granted, weighted average exercise price per share							$ 1.63
2017 Stock Incentive Plan [Member] \| Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units granted							50,000
Units granted, weighted average grant date fair value							$ 1.75
2016 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period							4 years
Stock option expiration period							10 years
Number of shares issued							0
2016 Stock Incentive Plan [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance				424,601			424,601
2017 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance			150,000
Maximum annual increase in common stock reserved for future issuance			622,408
Percentage of common stock shares outstanding			1.00%
Increase to shares authorized for issuance	0	0
Stock incentive plan description					On June 16, 2017, the Company’s stockholders approved the 2017 Employee Stock Purchase Plan (the “2017 ESPP”), which became effective on June 28, 2017. A total of 150,000 shares of common stock were initially reserved for issuance under this plan. The number of shares of common stock that may be issued under the 2017 ESPP will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2018 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the least of (i) 622,408 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors. On December 13, 2018, the Company’s compensation committee of the board of directors determined that the number of shares of common stock that may be issued under the 2017 ESPP would not be increased on January 1, 2018 or January 1, 2019.
2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period							4 years
Stock option expiration period							10 years
Number of shares issued							0
Stock incentive plan termination year							2016
Maximum [Member] \| 2017 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period							4 years
Stock option expiration period							10 years
Maximum [Member] \| 2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period							4 years

Stock-Based Awards - Summary of Stock Option Activity (Detail) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance	2,528,297
Number of Shares, Granted	1,692,150
Number of Shares, Exercised	(126,560)
Number of Shares, Canceled	(66,540)
Number of Shares, Forfeited	(149,879)
Number of Shares, Ending balance	3,877,468	2,528,297
Number of Shares, Options exercisable	1,299,550	1,214,016
Number of Shares, Options vested and expected to vest	3,784,829	2,485,495
Weighted Average Exercise Price, Beginning balance	$ 6.31
Weighted Average Exercise Price, Granted	1.63
Weighted Average Exercise Price, Exercised	1.30
Weighted Average Exercise Price,Canceled	3.52
Weighted Average Exercise Price, Forfeited	7.26
Weighted Average Exercise Price, Ending balance	4.44	$ 6.31
Weighted Average Exercise Price, Options exercisable	6.80	6.29
Weighted Average Exercise Price, Options vested and expected to vest	$ 6.80	$ 6.31
Weighted-Average Remaining Contractual Term, Outstanding	7 years 10 months 24 days	6 years 8 months 12 days
Weighted Average Remaining Contractual Term, Options exercisable	4 years 9 months 18 days	3 years 10 months 24 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	4 years 9 months 18 days	6 years 7 months 6 days

Commitments and Contingencies - Additional Information (Detail)		1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 04, 2018 USD ($) ft² $ / ft²	Oct. 31, 2010 USD ($)	Feb. 28, 2010 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Option Milestone	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2006 USD ($)
Other Commitments [Line Items]
Operating lease, right-of-use asset				$ 6,385,000		$ 6,385,000
Operating lease, liability				5,228,000		$ 5,228,000
ASU No. 2016-02 [Member]
Other Commitments [Line Items]
Operating lease, right-of-use asset									$ 6,697,000
Operating lease, liability									$ 5,401,000
Operating Lease Agreements [Member] \| Building [Member]
Other Commitments [Line Items]
Lessee, Operating Lease, Existence of Option to Extend [true false]						true
Lessee Operating Lease Option To Extend						The Company has the option to extend the 490 Arsenal Way Lease for one five-year terms.
Harvard and Dana-Farber Agreement [Member]
Other Commitments [Line Items]
Milestone payments				0	$ 0	$ 0	$ 0
Milestones achieved \| Milestone						0
Additional liabilities for milestone payments				0		$ 0
Non-refundable cash payment						4,718,000		$ 4,573,000
Payments for royalties						0
Harvard and Dana-Farber Agreement [Member] \| Therapeutic Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments			$ 7,700,000
Harvard and Dana-Farber Agreement [Member] \| Diagnostic Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments			700,000
Harvard and Dana-Farber Agreement [Member] \| License and Maintenance [Member]
Other Commitments [Line Items]
Annual license maintenance fees			$ 145,000
Harvard and Dana-Farber Agreement [Member] \| License [Member]
Other Commitments [Line Items]
Annual license maintenance fees						145,000	145,000
Umicore Agreement [Member]
Other Commitments [Line Items]
Aggregate milestones payments										$ 6,400,000
Milestone payments				0	0	$ 0	0
Milestones achieved \| Milestone						0
Additional liabilities for milestone payments				0		$ 0
Umicore Agreement [Member] \| License and Maintenance [Member]
Other Commitments [Line Items]
Annual license maintenance fees						50,000
Umicore Agreement [Member] \| License [Member]
Other Commitments [Line Items]
Annual license maintenance fees						$ 50,000	0
Scripps Agreement [Member]
Other Commitments [Line Items]
Milestones achieved \| Milestone						0
Additional liabilities for milestone payments				0		$ 0
Payments for royalties						0
Scripps Agreement [Member] \| License and Maintenance [Member]
Other Commitments [Line Items]
Annual license maintenance fees		$ 50,000
Scripps Agreement [Member] \| License [Member]
Other Commitments [Line Items]
Annual license maintenance fees				$ 0	$ 0	$ 0	$ 0
Scripps Agreement [Member] \| Peptide Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments		1,900,000
Scripps Agreement [Member] \| Protein Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments		$ 950,000
Watertown, Massachusetts [Member] \| Operating Lease Agreements [Member] \| 490 Arsenal Way [Member] \| Building [Member]
Other Commitments [Line Items]
Area of Land \| ft²	18,768
Operating lease price per square foot per year \| $ / ft²	52.55
Base rent per year	$ 986,000
Security deposit	568,000
Cost of construction and tenant improvements	$ 2,419,000
Period of contract						Aug. 31, 2026
Number of option to extend \| Option						1
Lease initial term				8 years		8 years
Lease extension term				5 years		5 years
Building in service over a useful life						30 years

Commitments and Contingencies - Future Minimum Commitments Under ASC 842 Under Operating Leases (Detail) $ in Thousands	Jun. 30, 2019 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019 (excluding the six months ended June 30, 2019)	$ 504
2020	1,026
2021	1,058
2022	1,089
2023	1,122
2024 and thereafter	3,126
Total lease payments	7,925
Less: imputed interest	(2,697)
Total operating lease liabilities	$ 5,228

Commitments and Contingencies - Future Minimum Commitments Under ASC 840 Under Operating Leases (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 997
2020	1,026
2021	1,058
2022	1,089
2023	1,122
2024 and thereafter	3,126
Total lease payments	$ 8,418

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current	$ 25	$ 25
Restricted cash, non-current	568	568
490 Arsenal Way [Member] \| Operating Lease Agreements [Member] \| ASU No. 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
De-recognized building asset	7,079
De-recognition of accumulated depreciation	81
Security Deposit Related to Credit Card Accounts [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current	25	25
Security Deposit Related to Lease Facility [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, non-current	$ 568	$ 568

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
External research and development services	$ 1,243	$ 1,307
Payroll and payroll-related costs	994	1,473
Professional fees	663	436
Other	362	423
Total accrued expenses and other current liabilities	$ 3,262	$ 3,639

Stock-Based Awards - Valuation Assumptions of Stock Options Granted (Detail)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	2.35%	2.75%
Expected term (in years)	6 years 3 months 18 days	6 years 2 months 12 days
Expected volatility	76.00%	76.00%
Expected dividend yield	0.00%	0.00%

Stock-Based Awards - Summary of Restricted Stock Unit Activity (Detail) - 2017 Stock Incentive Plan [Member] - Restricted Stock Units [Member]	6 Months Ended
	Jun. 30, 2019 $ / shares shares
Units
Issued \| shares	50,000
Ending balance \| shares	50,000
Weighted-Average Grant Date per Unit
Issued \| $ / shares	$ 1.75
Ending balance \| $ / shares	$ 1.75

Net Loss per Share - Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	16,862,791	2,037,762
Stock Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	3,877,468	2,037,762
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	12,935,323
Restricted Stock Units to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	50,000

Condensed Statement of Stockholders' Equity (Deficit) (Unaudited) (Parenthetical) $ in Thousands	3 Months Ended
	Jun. 30, 2019 USD ($)
Common Stock and Common Warrants [Member]
Sale of common stock and common warrants, Issuance costs	$ 2,175

Investments - Summary of Fair Value of Available for Sale Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	$ 21,341	$ 10,065
Investments, Gross Unrealized Gain	24
Investments, Gross Unrealized Loss		(5)
Investments, Fair Value	21,365	10,060
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	13,684	3,647
Investments, Gross Unrealized Gain	13
Investments, Gross Unrealized Loss		(3)
Investments, Fair Value	13,697	3,644
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	7,657	6,418
Investments, Gross Unrealized Gain	11
Investments, Gross Unrealized Loss		(2)
Investments, Fair Value	$ 7,668	$ 6,416