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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2018	May 09, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Period Focus	Q1
Document Fiscal Year Focus	2018
Entity Registrant Name	resTORbio, Inc.
Entity Central Index Key	0001720580
Trading Symbol	TORC
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		28,046,315

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 135,705	$ 53,349
Prepaid expenses	986	792
Deferred offering costs		929
Other current assets	154	84
Total current assets	136,845	55,154
Restricted cash	84	0
Property and equipment, net	316	39
Total assets	137,245	55,193
Current liabilities:
Accounts payable (including related party amounts of $37 and $32 as of March 31, 2018 and December 31, 2017, respectively)	1,480	1,515
Accrued liabilities	4,854	3,987
Funding advance	500
Total current liabilities	6,834	5,502
Other liabilities	28
Total liabilities	6,862	5,502
Commitments and contingencies (see Note 9)
Stockholders’ equity (deficit):
Preferred stock, $0.0001 par value, 10,000,000 and no shares authorized as of March 31, 2018 and December 31, 2017, respectively; no shares issued and outstanding as of March 31, 2018 and December 31, 2017
Common stock, $0.0001 par value, 150,000,000 and 30,000,000 shares authorized as of March 31, 2018 and December 31, 2017, respectively; 28,046,315 and 5,659,089 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively; 28,046,315 and 4,562,640 shares vested as of March 31, 2018 and December 31, 2017, respectively	3	1
Additional paid-in capital	174,018	1,849
Accumulated deficit	(43,638)	(33,779)
Total stockholders’ equity (deficit)	130,383	(31,929)
Total liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit)	$ 137,245	55,193
Series A Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock		41,674
Series B Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock		$ 39,946

Condensed Consolidated Balance Sheets (Parenthetical) (unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts payable to related parties	$ 37	$ 32
Preferred stock, shares authorized		20,320,667
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	30,000,000
Common stock, shares issued	28,046,315	5,659,089
Common stock, shares outstanding	28,046,315	5,659,089
Common stock, shares vested	28,046,315	4,562,640
Series A Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	15,527,951
Preferred stock, shares issued	0	15,527,951
Preferred stock, shares outstanding	0	15,527,951
Series B Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	4,792,716
Preferred stock, shares issued	0	4,792,716
Preferred stock, shares outstanding	0	4,792,716

Condensed Consolidated Statements of Operations (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating expenses:
Research and development	$ 8,106	$ 3,294
General and administrative	2,094	63
Total operating expenses	10,200	3,357
Loss from operations	(10,200)	(3,357)
Other income, net	341	0
Loss before income taxes	(9,859)	(3,357)
Net loss	$ (9,859)	$ (3,357)
Net loss per share, basic and diluted	$ (0.46)	$ (1.20)
Weighted-average common shares used in computing net loss per share, basic and diluted	21,523,072	2,789,810

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities:
Net loss	$ (9,859)	$ (3,357)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	9
Stock-based compensation expense	1,181	125
Expense related to acquisition of intellectual property (see Note 5)		3,157
Changes in operating assets and liabilities:
Restricted cash	(84)
Prepaid expenses and other current assets	(264)	(229)
Accounts payable	80	10
Accrued liabilities	1,105
Funding advance	500
Other liabilities	28
Net cash used in operating activities	(7,304)	(294)
Investing activities:
Purchases of property and equipment	(278)
Net cash used in investing activities	(278)
Financing activities:
Proceeds from issuance of Series A redeemable convertible preferred stock		294
Proceeds from initial public offering, net of issuance costs	89,938
Net cash provided by financing activities	89,938	$ 294
Net increase in cash and cash equivalents	82,356
Cash and cash equivalents at beginning of period	53,349
Cash and cash equivalents at end of period	135,705
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable	8
Conversion of redeemable convertible preferred stock into common stock	$ 81,620

Organization	3 Months Ended
Organization	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	1. Organization resTORbio, Inc. (collectively referred to with its wholly-owned, controlled subsidiary, resTORbio Securities Corp. as “resTORbio” or the “Company”) was incorporated in the State of Delaware on July 5, 2016. The Company is a clinical-stage biopharmaceutical company focused on the development and commercialization of novel therapeutics for the treatment of aging-related diseases and conditions. The Company’s principal operations are located in Boston, Massachusetts. Since inception, the Company has been primarily involved in research and development activities. The Company devotes substantially all of its efforts to product research and development, initial market development and raising capital. The Company has not generated any product revenue related to its primary business purpose to date and is subject to a number of risks similar to those of other early stage companies, including dependence on key individuals, competition from other companies, the need for development of commercially viable products and the need to obtain adequate additional financing to fund the development of its product candidates. The Company is also subject to a number of risks similar to other companies in the life sciences industry, including regulatory approval of products, uncertainty of market acceptance of products, competition from substitute products and larger companies, the need to obtain additional financing, compliance with government regulations, protection of proprietary technology, dependence on third parties, product liability and dependence on key individuals. Reverse Stock Split On January 12, 2018, the Company effected a one-for-1.2804 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s redeemable convertible preferred stock (see Note 7). Accordingly, all share and per share amounts for all periods presented in the accompanying condensed consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the preferred stock conversion ratios. Initial Public Offering On January 30, 2018, the Company completed its initial public offering (“IPO”), whereby the Company sold 6,516,667 shares of its common stock (inclusive of 850,000 shares of common stock sold by the Company pursuant to the full exercise of an overallotment option granted to the underwriters in connection with the offering) at a price of $15.00 per share. The shares began trading on The Nasdaq Global Select Market on January 26, 2018. The aggregate net proceeds received by the Company from the offering were approximately $89.4 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company of $8.4 million. Upon the closing of the IPO, all outstanding shares of redeemable convertible preferred stock converted into 15,870,559 shares of common stock and all unvested shares of restricted stock automatically vested. Additionally, the Company is now authorized to issue 150,000,000 shares of common stock and 10,000,000 shares of preferred stock. Liquidity In the course of its development activities, the Company has sustained operating losses and expects such losses to continue over the next several years. The Company’s ultimate success depends on the outcome of its research and development activities. The Company has incurred net losses from operations since inception and has an accumulated deficit of $43.6 million as of March 31, 2018. On January 30, 2018, the Company completed its IPO whereby the Company sold 6,516,667 shares of its common stock for aggregate net proceeds of approximately $89.4 million. As of March 31, 2018, the Company had $135.7 million of cash and cash equivalents, which the Company believes will be sufficient to fund the Company’s current operating plan through at least the next twelve months.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The accompanying condensed consolidated financial statements are unaudited. The unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and, in the opinion of management, reflect all adjustments of a normal recurring nature necessary for a fair statement of the Company's financial position at March 31, 2018 and its results of operations, cash flows, and stockholders' equity (deficit) for the three months ended March 31, 2018 and 2017. The condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 that was filed with the Securities and Exchange Commission (“SEC”) on March 29, 2018 (the “2017 Form 10-K”). Interim results are not necessarily indicative of results for a full year or for any other interim period.

The condensed consolidated financial statements include the accounts of resTORbio, Inc. and its wholly owned subsidiary, resTORbio Securities Corp. All inter-company transactions and balances have been eliminated in consolidation.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities, as of the date of the condensed consolidated financial statements, and the reported amounts of any expenses during the reporting period. On an ongoing basis, management evaluates its estimates, including those related to accrued liabilities, fair value of common stock, income taxes and stock-based compensation expense. Management bases its estimates on historical experience, and on various other market-specific relevant assumptions that management believes to be reasonable, under the circumstances. Actual results may differ from those estimates or assumptions.

Summary of Significant Accounting Policies

The significant accounting policies and estimates used in the preparation of the condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2017, and the notes thereto, which are included in the 2017 Form 10-K. There have been no material changes in the Company’s significant accounting policies during the three months ended March 31, 2018.

Restricted Cash

The Company maintains a letter of credit for the benefit of the landlord in connection with the Company’s office lease. As of March 31, 2018 and December 31, 2017, restricted cash (non-current) consisted of $0.1 million and $0, respectively, held for the benefit of the landlord in connection with the Company’s office lease.

Fair Value Measurements

Fair value is defined as the price at which an asset could be exchanged in a current transaction between knowledgeable, willing parties. The authoritative accounting guidance describes a fair value hierarchy based on three levels of inputs that may be used to measure fair value, of which the first two are considered observable and the last is considered unobservable. These levels of inputs are as follows:

Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date.

Level 2—Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable for the asset or liability. These include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active.

Level 3—Unobservable inputs that reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model.

The following table summarizes assets measured at fair value on a recurring basis at March 31, 2018 (in thousands):

			Active		Observable		Unobservable
	March 31,		Markets		Inputs		Inputs
Description	2018		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash equivalents	$	135,705	$	135,705		—		—
Restricted cash		84		84		—		—
Total assets	$	135,789	$	135,789	$	—	$	—

The following table summarizes assets measured at fair value on a recurring basis at December 31, 2017 (in thousands):

			Active		Observable		Unobservable
	December 31,		Markets		Inputs		Inputs
Description	2017		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash equivalents	$	53,349	$	53,349		—		—
Restricted cash		—		—		—		—
Total assets	$	53,349	$	53,349	$	—	$	—

Deferred Offering Costs

The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of proceeds generated as a result of the offering. Should the planned equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations. The Company recorded deferred offering costs of $0 and $0.9 million as of March 31, 2018 and December 31, 2017, respectively.

Property and Equipment

Property and equipment are stated at cost, less accumulated depreciation. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets. Depreciation begins at the time the asset is placed in service. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statements of operations.

The estimated useful lives of property and equipment are as follows:

		Useful Life (in years)
Leasehold improvements		Lesser of useful life or remaining lease term
Laboratory and manufacturing equipment		2-8 years
Computer equipment and software		1-5 years
Furniture and Fixtures		3-5 years
Office Equipment		3-5 years
Software		3-5 years

Recently Adopted Accounting Pronouncements

In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting (“ASU 2017-09”). ASU 2017-09 provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718. The guidance is effective for annual periods beginning after December 15, 2017, with early adoption permitted, including adoption in any interim period for which financial statements have not yet been issued. The Company adopted the provisions of ASU 2017-09 on January 1, 2018. No modifications of share-based payment awards have occurred as of March 31, 2018.

Recently Issued Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02, Leases (“ASU 2016-02”), which requires a lessee to recognize a right-of-use asset and a lease liability for operating leases, initially measured at the present value of the future lease payments, in the balance sheet. ASU 2016-02 also requires a lessee to recognize a single lease cost, calculated so that the cost of the lease is allocated over the lease term, generally on a straight-line basis. This new guidance is effective for fiscal years beginning after December 15, 2019. Early adoption is permitted. The Company is currently evaluating the potential effects of adopting the provisions of ASU 2016-02.

In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (“ASU 2016-18”), which requires that amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for fiscal years beginning after December 15, 2018 and interim periods in fiscal years beginning after December 15, 2019 and should be applied using a retrospective transition method to each period presented. Early adoption is permitted. The Company does not expect the impact of ASU 2016-18 to be material to its consolidated financial statements.

In July 2017, the FASB issued ASU 2017-11, Accounting for Certain Financial Instruments with Down Round Features (“ASU 2017-11”), which updates the guidance related to the classification analysis of certain equity-linked financial instruments (or embedded features) with down round features. Under ASU 2017-11, a down round feature no longer precludes equity classification when assessing whether the instrument is indexed to an entity’s own stock. As a result, a freestanding equity-linked financial instrument (or embedded conversion option) no longer would be accounted for as a derivative liability at fair value as a result of the existence of a down round feature. For freestanding equity classified financial instruments, the amendments require entities that present earnings per share (“EPS”) in accordance with Topic 260 to recognize the effect of the down round feature when it is triggered. That effect is treated as a dividend and as a reduction of income available to common shareholders in basic EPS. ASU 2017-11 is effective for public entities for all annual and interim periods beginning after December 15, 2019. Early adoption is permitted. The Company is currently evaluating the impact that the adoption of ASU 2017-11 will have on its consolidated financial statements.

Property and Equipment, Net

3 Months Ended

Mar. 31, 2018

Property Plant And Equipment [Abstract]

Property and Equipment, Net

3. Property and equipment, net

Property and equipment, net consists of the following:

	As of March 31, 2018			As of December 31, 2017
	(In thousands)
Leasehold improvements	$	60		$	—
Machinery and equipment		38			38
Furniture and fixtures		167			—
Computers		34			6
Office equipment		9			—
Software		22			—
Total property and equipment		330			44
Less: accumulated depreciation		(14	)		(5	)
Property and equipment, net	$	316		$	39

Depreciation expense was $9,000 and $0 for the three months ended March 31, 2018 and 2017, respectively.

Accrued Liabilities

3 Months Ended

Mar. 31, 2018

Payables And Accruals [Abstract]

Accrued Liabilities

4. Accrued Liabilities

Accrued liabilities consist of the following:

	As of March 31, 2018		As of December 31, 2017
	(In thousands)
Accrued payroll and related expenses	$	233	$	394
Accrued research and development expenses		4,418		3,250
Deferred offering costs		—		238
Other		203		105
Total accrued liabilities	$	4,854	$	3,987

License Agreements	3 Months Ended
License Agreements	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
License Agreements	5. License Agreements Novartis License Agreement On March 23, 2017, the Company entered into an exclusive license agreement with Novartis International Pharmaceutical Ltd. (“Novartis”). Under the agreement, Novartis granted the Company an exclusive, field-restricted, worldwide license, to certain intellectual property rights owned or controlled by Novartis, to develop, commercialize and sell one or more therapeutic products comprising RTB101 or RTB101 in combination with everolimus in a fixed dose combination. The exclusive field under the license agreement is for the treatment, prevention and diagnosis of disease and other conditions in all indications in humans and animals. As initial consideration for the licensed rights, the Company issued Novartis Institutes for Biomedical Research (“NIBR”) 2,587,992 shares of the Company’s Series A Preferred Stock. The fair value of the Novartis license was $3.2 million based on the fair value of the Series A Preferred Stock which was determined to be $1.22 per share based on an independent third-party valuation, and is recorded as research and development expenses in the consolidated statements of operations. The agreement may be terminated by either party upon a material breach by the other party that is not cured within 60 days after written notice. The Company may terminate the agreement in its entirety or on a product-by-product or country-by-country basis with or without cause with 60 days’ prior written notice. Novartis may terminate the portion of the agreement related to everolimus if the Company fails to use commercially reasonable efforts to research, develop and commercialize a product utilizing everolimus for a period of three years. Novartis may terminate the license agreement upon the Company’s bankruptcy, insolvency, dissolution or winding up. As additional consideration for the license, the Company is required to pay up to an aggregate of $4.3 million upon the satisfaction of clinical milestones, up to an aggregate of $24 million upon the satisfaction of regulatory milestones for the first indication approved, and up to an aggregate of $18 million upon the satisfaction of regulatory milestones for the second indication approved. In addition, the Company is required to pay up to an aggregate of $125 million upon the satisfaction of commercial milestones, based on the amount of annual net sales. The Company is also required to pay tiered royalties ranging from a mid single-digit percentage to a low teen-digit percentage on annual net sales of products. These royalty obligations last on a product-by-product and country-by-country basis until the latest of (i) the expiration of the last valid claim of a Novartis patent covering a subject product, (ii) the expiration of any regulatory exclusivity for the subject product in a country, or (iii) the 10^th anniversary of the first commercial sale in the country, and are subject to a reduction after the expiration of the last valid claim of a Novartis patent or the introduction of a generic equivalent of a product in a country. In addition, if the Company sublicenses the rights under the license agreement, the Company is required to pay a certain percentage of sublicense revenue to Novartis. Novartis will no longer be entitled to sublicense revenue following the last visit of the 400^th subject in any human clinical trial conducted by the Company or a sublicensee of the Company. Milestone payments to Novartis will be recorded as research and development expenses in the consolidated statements of operations once achievement of each associated milestone has occurred or the achievement is considered probable. In May 2017, the Company initiated a Phase 2b clinical trial for a first indication, triggering the first milestone payment under the agreement. Accordingly, the Company paid the related $0.3 million milestone in May 2017. As of March 31, 2018, none of the remaining development milestones, regulatory milestones, sales milestones, or royalties had been reached or were probable of achievement.

Research Funding Agreements	3 Months Ended
Research Funding Agreements	Mar. 31, 2018
Research Funding Agreement [Abstract]
Research Funding Agreement	6. Research Funding Agreement On March 6, 2018, the Company and the Silverstein Foundation for Parkinson’s with GBA (the “Silverstein Foundation”) entered into a research funding agreement (the “Funding Agreement”). One of the Company’s directors is a co-founder and current trustee of the Silverstein Foundation. Under the terms of the Funding Agreement, the Silverstein Foundation will partially fund the preclinical research, development work, and Phase 2 clinical trial expenses (the “Research”) to be conducted and borne by the Company in connection with the development of RTB101 product, alone or in combination with other products (the “Product”). Upon execution of the Funding Agreement, the Silverstein Foundation paid the Company an upfront sum of $0.5 million (the “Funding Amount”). The Company is entitled to use the Funding Amount solely to conduct the Research and is obligated to repay the Funding Amount in full to the Silverstein Foundation if it successfully conducts a positive Phase 3 clinical trial of the Product for Parkinson’s Disease. The Company is solely responsible for commencing and conducting the Research and will furnish periodic progress updates to the Silverstein Foundation throughout the term of the Funding Agreement. After completing the Research, the Company must provide the Silverstein Foundation with a formal report describing the work performed and the results of the Research. The Company recognizes proceeds received from the Silverstein Foundation as a reduction to research and development expenses, rather than as revenue, in the condensed consolidated statements of operations because the corresponding Funding Agreement does not contain specified performance obligations other than to conduct research on a particular program or in a particular field and contain no obligations to deliver specified products or technology. For funds received under the agreement with the Silverstein Foundation, the Company recognizes a reduction in research and development expenses in an amount equal to the qualifying expenses incurred in each period, up to the amount funded by the Silverstein Foundation. Funding that has been received by the Company in advance of incurring qualifying expenses is recorded in the condensed consolidated balance sheet as funding advance. As of March 31, 2018, no qualifying expenses have been incurred.

Redeemable Convertible Preferred Stock and Common Stock

3 Months Ended

Mar. 31, 2018

Temporary Equity Disclosure [Abstract]

Redeemable Convertible Preferred Stock and Common Stock

7. Redeemable Convertible Preferred Stock and Common Stock

As of March 31, 2018, the Company had 10,000,000 shares of preferred stock authorized and none issued and outstanding. As of December 31, 2017, the Company had 20,320,667 shares of preferred stock authorized, of which 15,527,951 shares were issued and outstanding and were designated as $0.0001 par value Series A Preferred Stock and 4,792,716 shares were issued and outstanding and were designated as $0.0001 par value Series B Preferred Stock.

Upon completion of the Company’s initial public offering in January 2018, all the outstanding preferred stock of the Company automatically converted into 15,870,559 shares of the Company’s common stock. As of March 31, 2018, no shares of preferred stock were outstanding.

Reserve for future issuance

The Company has reserved the following number of shares of common stock for future issuance upon the conversion of preferred stock, exercise of options or grant of equity awards:

	As of March 31, 2018		As of December 31, 2017
Redeemable convertible preferred stock, on an as-converted basis		—		15,870,559
Options issued and outstanding		667,590		195,668
Options available for future grants		1,839,658		1,670,341
Shares available for issuance under the 2018 ESPP		275,030		—
Total		2,782,278		17,736,568

On January 12, 2018, the Company effected a one-for-1.2804 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s preferred stock (see Note 1).

Stock-Based Compensation

3 Months Ended

Mar. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

8. Stock-based Compensation

In 2017, the Company adopted the 2017 Stock Incentive Plan (the “2017 Plan”). Under the 2017 Plan, shares of the Company’s common stock have been reserved for the issuance of stock options to employees, directors, and consultants under terms and provisions established by the Board of Directors. A total of 537,914 shares were reserved for issuance under the 2017 Plan. Under the terms of the 2017 Plan, options may be granted at an exercise price not less than fair market value. The terms of options granted under the 2017 Plan may not exceed ten years. The Board shall determine the terms and conditions of a Restricted Stock Award, including the conditions for vesting and repurchase (or forfeiture) and the issue price, if any. On October 11, 2017, the Company increased the number of shares of common stock available for issuance under the 2017 Plan from 537,914 shares to 630,662 shares. On November 29, 2017, the Company increased the number of shares of common stock available for issuance under the 2017 Plan from 630,662 shares to 1,866,009 shares.

In connection with the Company’s IPO, the Company’s Board of Directors adopted and the Company’s stockholders approved the 2018 stock incentive plan (“2018 Plan”), which became effective immediately prior to the closing of the Company’s IPO. The 2018 Plan provides for the grant of incentive stock options, nonstatutory stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock-based awards. The Company’s employees, officers, directors, consultants and advisors are eligible to receive awards under the 2018 Plan. The number of shares of common stock that are reserved for issuance under the 2018 Plan are 2,200,260 shares. The 2018 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2019, by 4% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Board of Directors.

On and after the effective date of the 2018 Plan, the Company will not grant any further awards under the 2017 Plan. However, any shares of common stock subject to awards under the 2017 Plan that expire, terminate, or otherwise are surrendered, canceled, forfeited or repurchased without having been fully exercised or resulting in any common stock being issued will become available for issuance under the 2018 Plan.

Stock-based Compensation Expense

Total stock-based compensation expense is recognized for stock options granted to employees and non-employees and has been reported in the Company’s consolidated statements of operations as follows:

	Three Months Ended March 31,
	2018		2017
Research and development	$	625	$	62
General and administrative		556		63
Total stock-based compensation expense	$	1,181	$	125

Stock Options

The following table summarizes stock option activity under the Plans:

	Shares Available for Grant			Number of Options Outstanding		Weighted- Average Exercise Price per Option		Weighted- Average Remaining Contract Term	Aggregate Intrinsic Value
									(In thousands)
Outstanding, December 31, 2017		1,670,341			195,668	$	4.49	9.67
Shares reserved for issuance		641,239
Options granted⁽¹⁾		(471,922	)		471,922		14.60
Outstanding, March 31, 2018		1,839,658			667,590		11.63	9.71	$	1,048
Exercisable, March 31, 2018					—		—
Vested and expected to vest, March 31, 2018					667,590		11.63	9.71	$	1,048

(1)	The Company granted 7,200 stock options to non-employees during the three months ended March 31, 2018.

The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock as of March 31, 2018. No options were exercised, cancelled or forfeited during the three months ended March 31, 2018.

During the three months ended March 31, 2018, the Company granted options to employees and directors to purchase an aggregate of 464,722 common shares with a weighted-average grant date fair value of $9.88 per share. During the three months ended March 31, 2018, the Company granted options to non-employees to purchase an aggregate of 7,200 common shares with a weighted-average grant date fair value of $12.51 per share. The expense related to options granted to employees and directors and non-employees was $0.3 million and $3,000, respectively, for the three months ended March 31, 2018. There were no stock options granted to employees or non-employees during the three months ended March 31, 2017.

As of March 31, 2018, the total unrecognized compensation expense related to unvested employee options was $5.0 million, which the Company expects to recognize over an estimated weighted-average period of 3.68 years. As of March 31, 2018, the total unrecognized compensation expense related to unvested non-employee options was $0.3 million, which the Company expects to recognize over an estimated weighted-average period of 3.43 years.

The fair value of stock options for employees and non-employees was estimated using a Black-Scholes option pricing model with the following assumptions:

	Three Months Ended March 31, 2018
Employees:
Fair value of common stock	$13.17 - $15.45
Expected term (in years)	5.8-6.6
Expected volatility	76.1%-77.7%
Risk-free interest rate	2.4%-2.7%
Expected dividend yield	0.0%
Non-employees:
Fair value of common stock	$	15.45
Expected term (in years)		10.0
Expected volatility	77.9%
Risk-free interest rate	2.7%
Expected dividend yield	0.0%

Restricted Stock

On July 11, 2016, certain founders purchased 3,772,726 common shares that are subject to a repurchase right upon termination or cessation of services at the original purchase price of $0.0001 per share, or $483. The repurchase right lapses as vesting occurs. Compensation expense of such unvested shares was remeasured at fair value until vested at each reporting date. On April 4, 2017, the non-employee directors became employees of the Company and as a result, compensation expense of the unvested shares was remeasured at fair value and fixed and was being recognized over the remaining vesting period. Upon the closing of the Series A preferred financing, a portion of the unvested shares accelerated and vested in full. Upon the Company’s IPO, the remaining unvested shares accelerated and vested in full. The summary of restricted stock activity and related information follows:

	Number of Restricted Shares Outstanding
Unvested shares — December 31, 2017		1,096,449
Vested		(1,096,449	)
Unvested shares — March 31, 2018		—

The Company recognized $0.9 million and $125,000 of stock-based compensation expense related to restricted shares during the three months ended March 31, 2018 and 2017, respectively. As of March 31, 2018, there was no unrecognized stock-based compensation expense related to unvested restricted stock.

2018 Employee Stock Purchase Plan

The Company’s Board of Directors adopted and the Company’s stockholders approved the 2018 employee stock purchase plan (“2018 ESPP”), which will become effective on a date determined by the Company’s Board of Directors. Once effective, the 2018 ESPP will enable eligible employees to purchase shares of the Company’s Common Stock at a discount. The number of shares of common stock that are reserved for issuance under the 2018 ESPP are 275,030 shares. The 2018 ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2019 and increasing each January 1 thereafter through January 1, 2028, by the least of (i) 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31; (ii) 543,926 shares or (iii) such number of shares as determined by the ESPP administrator.

Commitments and Contingences	3 Months Ended
Commitments and Contingences	Mar. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingences	9. Commitments and Contingences Litigation The Company is not a party to any litigation and does not have contingency reserves established for any litigation liabilities as of March 31, 2018 and December 31, 2017.

Net Loss Per Share

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Net Loss per Share

10. Net Loss per Share

The Company computes basic and diluted earnings (losses) per share using a methodology that gives effect to the impact of outstanding participating securities (the “two-class” method). Basic net loss per share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period and excludes any dilutive effects of share-based awards. Diluted net loss per share is computed giving effect to all potential dilutive common shares, including common stock issuable upon exercise of stock options, convertible preferred stock, and unvested restricted common stock. As the Company had net losses for the three months ended March 31, 2018 and 2017, there is no income allocation required under the two-class method or dilution attributed to weighted average shares outstanding in the calculation of diluted loss per share.

The following potentially dilutive securities have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive effect (in common stock equivalent shares):

	Three Months Ended March 31,
	2018		2017
Redeemable convertible preferred stock		—		2,021,237
Options issued and outstanding		667,590		—
Total		667,590		2,021,237

Related Party Transactions	3 Months Ended
Related Party Transactions	Mar. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	11. Related Party Transactions Since the Company’s incorporation in July 2016, the Company has engaged in transactions with related parties. The Company is a party to an intellectual property license agreement with Novartis. In addition, NIBR is a shareholder of the Company (See Note 5). No payments were made to Novartis during the three months ended March 31, 2018 and 2017. The Company is a party to a Funding Agreement with the Silverstein Foundation, an entity in which one of the Company’s directors is a co-founder and current trustee (See Note 6). The Company received $0.5 million from the Silverstein Foundation during the three months ended March 31, 2018. No funds were received during the three months ended March 31, 2017.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Summary of Significant Accounting Policies

Restricted Cash

Fair Value Measurements

Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date.

The following table summarizes assets measured at fair value on a recurring basis at March 31, 2018 (in thousands):

			Active		Observable		Unobservable
	March 31,		Markets		Inputs		Inputs
Description	2018		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash equivalents	$	135,705	$	135,705		—		—
Restricted cash		84		84		—		—
Total assets	$	135,789	$	135,789	$	—	$	—

The following table summarizes assets measured at fair value on a recurring basis at December 31, 2017 (in thousands):

			Active		Observable		Unobservable
	December 31,		Markets		Inputs		Inputs
Description	2017		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash equivalents	$	53,349	$	53,349		—		—
Restricted cash		—		—		—		—
Total assets	$	53,349	$	53,349	$	—	$	—

Deferred Offering Costs

Property and Equipment

The estimated useful lives of property and equipment are as follows:

		Useful Life (in years)
Leasehold improvements		Lesser of useful life or remaining lease term
Laboratory and manufacturing equipment		2-8 years
Computer equipment and software		1-5 years
Furniture and Fixtures		3-5 years
Office Equipment		3-5 years
Software		3-5 years

Recently Adopted Accounting Pronouncements

Recently Issued Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2018

Accounting Policies [Abstract]

Summary of Assets Measured at Fair Value on Recurring Basis

The following table summarizes assets measured at fair value on a recurring basis at March 31, 2018 (in thousands):

			Active		Observable		Unobservable
	March 31,		Markets		Inputs		Inputs
Description	2018		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash equivalents	$	135,705	$	135,705		—		—
Restricted cash		84		84		—		—
Total assets	$	135,789	$	135,789	$	—	$	—

The following table summarizes assets measured at fair value on a recurring basis at December 31, 2017 (in thousands):

			Active		Observable		Unobservable
	December 31,		Markets		Inputs		Inputs
Description	2017		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash equivalents	$	53,349	$	53,349		—		—
Restricted cash		—		—		—		—
Total assets	$	53,349	$	53,349	$	—	$	—

Schedule of Estimated Useful Lives of Property and Equipment

The estimated useful lives of property and equipment are as follows:

		Useful Life (in years)
Leasehold improvements		Lesser of useful life or remaining lease term
Laboratory and manufacturing equipment		2-8 years
Computer equipment and software		1-5 years
Furniture and Fixtures		3-5 years
Office Equipment		3-5 years
Software		3-5 years

- Definition

Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances.

+ References + Details

Property and Equipment, Net (Tables)

3 Months Ended

Mar. 31, 2018

Property Plant And Equipment [Abstract]

Summary of Property and Equipment, Net

Property and equipment, net consists of the following:

	As of March 31, 2018			As of December 31, 2017
	(In thousands)
Leasehold improvements	$	60		$	—
Machinery and equipment		38			38
Furniture and fixtures		167			—
Computers		34			6
Office equipment		9			—
Software		22			—
Total property and equipment		330			44
Less: accumulated depreciation		(14	)		(5	)
Property and equipment, net	$	316		$	39

Accrued Liabilities (Tables)

3 Months Ended

Mar. 31, 2018

Payables And Accruals [Abstract]

Summary of Accrued Liabilities

Accrued liabilities consist of the following:

	As of March 31, 2018		As of December 31, 2017
	(In thousands)
Accrued payroll and related expenses	$	233	$	394
Accrued research and development expenses		4,418		3,250
Deferred offering costs		—		238
Other		203		105
Total accrued liabilities	$	4,854	$	3,987

Redeemable Convertible Preferred Stock and Common Stock (Tables)

3 Months Ended

Mar. 31, 2018

Temporary Equity Disclosure [Abstract]

Schedule of Number of Shares of Common Stock Reserved for Future Issuance

The Company has reserved the following number of shares of common stock for future issuance upon the conversion of preferred stock, exercise of options or grant of equity awards:

	As of March 31, 2018		As of December 31, 2017
Redeemable convertible preferred stock, on an as-converted basis		—		15,870,559
Options issued and outstanding		667,590		195,668
Options available for future grants		1,839,658		1,670,341
Shares available for issuance under the 2018 ESPP		275,030		—
Total		2,782,278		17,736,568

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-Based Compensation Expense

	Three Months Ended March 31,
	2018		2017
Research and development	$	625	$	62
General and administrative		556		63
Total stock-based compensation expense	$	1,181	$	125

Summary of Stock Option Activity

The following table summarizes stock option activity under the Plans:

	Shares Available for Grant			Number of Options Outstanding		Weighted- Average Exercise Price per Option		Weighted- Average Remaining Contract Term	Aggregate Intrinsic Value
									(In thousands)
Outstanding, December 31, 2017		1,670,341			195,668	$	4.49	9.67
Shares reserved for issuance		641,239
Options granted⁽¹⁾		(471,922	)		471,922		14.60
Outstanding, March 31, 2018		1,839,658			667,590		11.63	9.71	$	1,048
Exercisable, March 31, 2018					—		—
Vested and expected to vest, March 31, 2018					667,590		11.63	9.71	$	1,048

(1)	The Company granted 7,200 stock options to non-employees during the three months ended March 31, 2018.

Schedule of Assumptions to Estimate Fair Value of Stock Options for Employees and Non-Employees Using Black-Scholes Option Pricing Model

The fair value of stock options for employees and non-employees was estimated using a Black-Scholes option pricing model with the following assumptions:

	Three Months Ended March 31, 2018
Employees:
Fair value of common stock	$13.17 - $15.45
Expected term (in years)	5.8-6.6
Expected volatility	76.1%-77.7%
Risk-free interest rate	2.4%-2.7%
Expected dividend yield	0.0%
Non-employees:
Fair value of common stock	$	15.45
Expected term (in years)		10.0
Expected volatility	77.9%
Risk-free interest rate	2.7%
Expected dividend yield	0.0%

Summary of Restricted Stock Activity

The summary of restricted stock activity and related information follows:

	Number of Restricted Shares Outstanding
Unvested shares — December 31, 2017		1,096,449
Vested		(1,096,449	)
Unvested shares — March 31, 2018		—

Net Loss Per Share (Tables)

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Schedule of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share

	Three Months Ended March 31,
	2018		2017
Redeemable convertible preferred stock		—		2,021,237
Options issued and outstanding		667,590		—
Total		667,590		2,021,237

Organization - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Jan. 30, 2018	Jan. 12, 2018	Mar. 31, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Entity incorporation date			Jul. 05, 2016
Reverse stock split effective date		Jan. 12, 2018
Reverse stock split description		one-for-1.2804	one-for-1.2804
Net proceeds received from offering			$ 89,938
Common stock, shares authorized			150,000,000	30,000,000
Preferred stock, shares authorized			10,000,000	0
Accumulated deficit			$ 43,638	$ 33,779
Cash and cash equivalents			$ 135,705	$ 53,349
Initial Public Offering
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of common stock shares sold	6,516,667
Issuance price per shares	$ 15.00
Net proceeds received from offering	$ 89,400
Payments for initial public offering after deducting underwriting discounts and commissions and other offering expenses	$ 8,400
Convertible preferred stock converted into common stock	15,870,559
Common stock, shares authorized	150,000,000
Preferred stock, shares authorized	10,000,000
Over-allotment Option
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of common stock shares sold	850,000

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Restricted cash (non-current)	$ 84	$ 0
Deferred offering costs	$ 0	$ 900

Summary of Significant Accounting Policies - Summary of Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	$ 135,705	$ 53,349
Restricted cash	84
Total assets	135,789	53,349
Active Markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	135,705	53,349
Restricted cash	84
Total assets	$ 135,789	$ 53,349

Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Property and Equipment (Details)	3 Months Ended
	Mar. 31, 2018
Laboratory and Manufacturing Equipment \| Minimum
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	2 years
Laboratory and Manufacturing Equipment \| Maximum
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	8 years
Computer Equipment and Software \| Minimum
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	1 year
Computer Equipment and Software \| Maximum
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	5 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	Lesser of useful life or remaining lease term
Furniture and Fixtures \| Minimum
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	3 years
Furniture and Fixtures \| Maximum
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	5 years
Office Equipment \| Minimum
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	3 years
Office Equipment \| Maximum
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	5 years
Software \| Minimum
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	3 years
Software \| Maximum
Property Plant And Equipment [Line Items]
Estimated useful lives of property and equipment	5 years

Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Total property and equipment	$ 330	$ 44
Less: accumulated depreciation	(14)	(5)
Property and equipment, net	316	39
Machinery and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	38	38
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	60
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	167
Computers
Property Plant And Equipment [Line Items]
Total property and equipment	34	$ 6
Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	9
Software
Property Plant And Equipment [Line Items]
Total property and equipment	$ 22

Property and Equipment, Net - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property Plant And Equipment [Abstract]
Depreciation expense	$ 9,000	$ 0

Accrued Liabilities - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued payroll and related expenses	$ 233	$ 394
Accrued research and development expenses	4,418	3,250
Deferred offering costs		238
Other	203	105
Total accrued liabilities	$ 4,854	$ 3,987

License Agreements - Additional Information (Details) - Novartis International Pharmaceutical Ltd. - License Agreement - USD ($)	1 Months Ended	3 Months Ended
	May 31, 2017	Mar. 31, 2018	Mar. 23, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement termination description		The agreement may be terminated by either party upon a material breach by the other party that is not cured within 60 days after written notice. The Company may terminate the agreement in its entirety or on a product-by-product or country-by-country basis with or without cause with 60 days’ prior written notice.
Milestone payment	$ 300,000
Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Aggregate amount payable upon satisfaction of clinical milestones			$ 4,300,000
Aggregate amount payable upon satisfaction of regulatory milestones for first indication approved			24,000,000
Aggregate amount payable upon satisfaction of regulatory milestones for second indication approved			18,000,000
Aggregate amount payable upon satisfaction of commercial milestones			$ 125,000,000
Series A Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued			2,587,992
Fair value of license agreement			$ 3,200,000
Fair value of shares issued			$ 1.22

Research Funding Agreement - Additional Information (Details) - Silverstein Foundation - Funding Agreement - USD ($)	Mar. 06, 2018	Mar. 31, 2018
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront sum of funding amount	$ 500,000
Qualifying expenses		$ 0

Redeemable Convertible Preferred Stock and Common Stock - Additional Information (Details)		3 Months Ended
	Jan. 12, 2018	Mar. 31, 2018 $ / shares shares	Jan. 31, 2018 shares	Jan. 30, 2018 shares	Dec. 31, 2017 $ / shares shares
Temporary Equity [Line Items]
Preferred stock, shares authorized		10,000,000			0
Preferred stock, shares authorized					20,320,667
Preferred stock, shares issued		0			0
Preferred stock, shares outstanding		0			0
Reverse stock split description	one-for-1.2804	one-for-1.2804
Reverse stock split ratio	0.781
Initial Public Offering
Temporary Equity [Line Items]
Preferred stock, shares authorized				10,000,000
Convertible preferred stock converted into common stock				15,870,559
Initial Public Offering \| Common Stock
Temporary Equity [Line Items]
Convertible preferred stock converted into common stock			15,870,559
Series A Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Preferred stock, shares authorized		0			15,527,951
Preferred stock, shares issued		0			15,527,951
Preferred stock, shares outstanding		0			15,527,951
Preferred stock, par value \| $ / shares		$ 0.0001			$ 0.0001
Series B Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Preferred stock, shares authorized		0			4,792,716
Preferred stock, shares issued		0			4,792,716
Preferred stock, shares outstanding		0			4,792,716
Preferred stock, par value \| $ / shares		$ 0.0001			$ 0.0001

Redeemable Convertible Preferred Stock and Common Stock -Schedule of Number of Shares of Common Stock Reserved for Future Issuance (Details) - shares	Mar. 31, 2018	Dec. 31, 2017
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	2,782,278	17,736,568
Redeemable Convertible Preferred Stock, on an as-converted Basis
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance		15,870,559
Options Issued and Outstanding
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	667,590	195,668
Options Available for Future Grants
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	1,839,658	1,670,341
Shares Available for Issuance under the 2018 ESPP
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	275,030

Stock-Based Compensation - Additional Information (Details) - USD ($)				3 Months Ended
	Nov. 29, 2017	Oct. 11, 2017	Jul. 11, 2016	Mar. 31, 2018	Mar. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Recognized stock-based compensation expense				$ 1,181,000	$ 125,000
Options Issued and Outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options exercised				0
Number of options cancelled or forfeited				0
Stock options granted				471,922
Options Issued and Outstanding \| Employees and Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted to purchase aggregate common shares				464,722
Weighted-average grant date fair value of options granted				$ 9.88
Expense related to options granted				$ 300,000
Options Issued and Outstanding \| Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted					0
Unrecognized compensation expense				$ 5,000,000
Unrecognized compensation expense, estimated weighted-average period for recognition				3 years 9 months 10 days
Options Issued and Outstanding \| Non-employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted to purchase aggregate common shares				7,200
Weighted-average grant date fair value of options granted				$ 12.51
Expense related to options granted				$ 3,000
Stock options granted				7,200	0
Unrecognized compensation expense				$ 300,000
Unrecognized compensation expense, estimated weighted-average period for recognition				3 years 5 months 12 days
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Recognized stock-based compensation expense				$ 900,000	$ 125,000
Unrecognized stock-based compensation expense				$ 0
Restricted Stock \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common shares issued, subject to repurchase right upon termination or cessation of service			3,772,726
Issuance price per shares			$ 0.0001
Common shares issued, value			$ 483
2017 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance	630,662	537,914		537,914
Number of additional shares reserved for issuance	1,866,009	630,662
2017 Stock Incentive Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Terms of stock based options granted				10 years
2018 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance				2,200,260
Percentage of additional shares added on outstanding shares				4.00%
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance				275,030
Number of additional shares reserved for issuance				543,926
Percentage of additional shares added on outstanding shares				1.00%

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - Employees And Non Employees - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,181	$ 125
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	625	62
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 556	$ 63

Stock-Based Compensation - Summary of Stock Option Activity (Details) - Options Issued and Outstanding - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, beginning, Shares Available for Grant	1,670,341
Shares reserved for issuance, Shares Available for Grant	641,239
Options granted, Shares Available for Grant	(471,922)
Outstanding, ending, Shares Available for Grant	1,839,658	1,670,341
Outstanding, beginning, Number of Options	195,668
Options granted, Number of Options	471,922
Outstanding, ending, Number of Options	667,590	195,668
Vested and expected to vest, Number of Options	667,590
Outstanding, beginning, Weighted-Average Exercise Price per Option	$ 4.49
Options granted, Weighted-Average Exercise Price per Option	14.60
Outstanding, ending, Weighted-Average Exercise Price per Option	11.63	$ 4.49
Vested and expected to vest, Weighted-Average Exercise Price per Option	$ 11.63
Outstanding, beginning, Weighted-Average Remaining Contract Term	9 years 8 months 16 days	9 years 8 months 1 day
Vested and expected to vest, Weighted-Average Remaining Contract Term	9 years 8 months 16 days
Outstanding, ending, Aggregate Intrinsic Value	$ 1,048
Vested and expected to vest, Aggregate Intrinsic Value	$ 1,048

Stock-Based Compensation - Summary of Stock Option Activity (Parenthetical) (Details) - Options Issued and Outstanding - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted	471,922
Non-employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted	7,200	0

Stock-Based Compensation - Schedule of Assumptions to Estimate Fair Value of Stock Options for Employees and Non-Employees Using Black-Scholes Option Pricing Model (Details) - Options Issued and Outstanding	3 Months Ended
	Mar. 31, 2018 $ / shares
Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	76.10%
Expected volatility, maximum	77.70%
Risk-free interest rate, minimum	2.40%
Risk-free interest rate, maximum	2.70%
Expected dividend yield	0.00%
Non-employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 15.45
Expected term (in years)	10 years
Expected dividend yield	0.00%
Expected volatility	77.90%
Risk-free interest rate	2.70%
Minimum \| Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 13.17
Expected term (in years)	5 years 9 months 18 days
Maximum \| Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 15.45
Expected term (in years)	6 years 7 months 6 days

Stock-Based Compensation - Summary of Restricted Stock Activity (Details) - Restricted Stock	3 Months Ended
	Mar. 31, 2018 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Restricted Shares Outstanding, Unvested shares — December 31, 2017	1,096,449
Number of Restricted Shares Outstanding, Vested	(1,096,449)

Commitment and Contingencies - Additional Information (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Estimated litigation liability	$ 0	$ 0

Net Loss Per Share - Schedule of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	667,590	2,021,237
Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		2,021,237
Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	667,590

Related Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Novartis
Related Party Transaction [Line Items]
Payments to related parties	$ 0	$ 0
Silverstein Foundation \| Funding Agreement
Related Party Transaction [Line Items]
Fund received from related parties	$ 500,000	$ 0