Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2017	Oct. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Trading Symbol	GTHX
Entity Registrant Name	G1 THERAPEUTICS, INC.
Entity Central Index Key	0001560241
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		28,345,284

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 118,380	$ 47,305
Prepaid expenses and other current assets	655	596
Total current assets	119,035	47,901
Property and equipment, net	516	311
Total assets	119,551	48,212
Current liabilities
Accounts payable	4,234	2,605
Accrued expenses	6,187	2,853
Warrant liability		167
Total current liabilities	10,421	5,625
Commitments and contingencies
Stockholders’ equity (deficit)
Common stock, $0.0001 par value, 120,000,000 shares and 73,000,000 shares authorized as of September 30, 2017 and December 31, 2016, respectively; 28,369,679 and 1,504,947 shares issued as of September 30, 2017 and December 31, 2016, respectively; 28,343,013 and 1,478,281 shares outstanding as of September 30, 2017 and December 31, 2016, respectively	3
Treasury stock, 26,666 shares	(8)	(8)
Additional paid-in capital	221,272
Accumulated deficit	(112,137)	(64,985)
Total stockholders’ equity (deficit)	109,130	(64,993)
Total liabilities, mezzanine equity and equity	$ 119,551	48,212
Series C Redeemable Convertible Preferred Stock
Mezzanine equity
Redeemable convertible preferred stock		51,424
Series B Redeemable Convertible Preferred Stock
Mezzanine equity
Redeemable convertible preferred stock		40,355
Series A Redeemable Convertible Preferred Stock
Mezzanine equity
Redeemable convertible preferred stock		14,431
Series 1 Redeemable Convertible Preferred Stock
Mezzanine equity
Redeemable convertible preferred stock		$ 1,370

Condensed Consolidated Balance Sheets (Parenthetical) (unaudited) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	120,000,000	73,000,000
Common stock, shares, issued	28,369,679	1,504,947
Common stock, shares, outstanding	28,343,013	1,478,281
Treasury stock, shares	26,666	26,666
Series C Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	17,000,000
Preferred stock, shares issued	0	5,609,398
Preferred stock, shares outstanding	0	5,609,398
Preferred stock, liquidation preference, value		$ 51,673
Series B Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	23,000,000
Preferred stock, shares issued	0	7,642,734
Preferred stock, shares outstanding	0	7,642,734
Preferred stock, liquidation preference, value		$ 35,722
Series A Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	14,996,692
Preferred stock, shares issued	0	4,998,895
Preferred stock, shares outstanding	0	4,998,895
Preferred stock, liquidation preference, value		$ 14,431
Series 1 Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	2,112,025
Preferred stock, shares issued	0	682,026
Preferred stock, shares outstanding	0	682,026
Preferred stock, liquidation preference, value		$ 931

Condensed Consolidated Statements of operations and comprehensive loss (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating expenses
Research and development	$ 14,054	$ 5,695	$ 38,806	$ 16,020
General and administrative	1,875	918	4,881	3,969
Total operating expenses	15,929	6,613	43,687	19,989
Operating loss	(15,929)	(6,613)	(43,687)	(19,989)
Other income (expense)
Other income	328	56	588	118
Change in fair value in warrant liability and other liabilities			(41)	(19)
Total other income, net	328	56	547	99
Net loss	(15,601)	(6,557)	(43,140)	(19,890)
Accretion of redeemable convertible preferred stock		(1,205)	(4,757)	(3,200)
Net loss attributable to common stockholders	$ (15,601)	$ (7,762)	$ (47,897)	$ (23,090)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.55)	$ (5.21)	$ (3.24)	$ (15.55)
Weighted average common shares outstanding, basic and diluted	28,318,656	1,490,552	14,772,621	1,484,713

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities
Net loss	$ (43,140)	$ (19,890)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	59	44
Stock-based compensation	2,357	908
Gain/loss on disposal of property and equipment	6	18
Increase in fair value of warrant activity	41	19
Change in operating assets and liabilities
Prepaid expenses and other assets	(59)	142
Accounts payable and accrued expenses	4,963	2,828
Net cash used in operating activities	(35,773)	(15,931)
Cash flows from investing activities
Purchases of property and equipment	(270)	(209)
Net cash used in investing activities	(270)	(209)
Cash flows from financing activities
Proceeds from stock options and warrants exercised	13	5
Issuance costs for preferred share financings		(249)
Proceeds from initial public offering, net of underwriting fees and commissions	108,503
Payment of public offering costs	(1,398)
Net cash provided by financing activities	107,118	49,756
Net change in cash and cash equivalents	71,075	33,616
Cash and cash equivalents
Beginning of period	47,305	22,938
End of period	118,380	56,554
Non-cash investing and financing activities
Accretion of redeemable convertible preferred stock	4,757	3,200
Conversion of preferred stock and preferred warrants to common stock and common warrants	112,337
Deferred offering costs reclassified to additional paid-in capital	$ 1,398
Series C Preferred Stock
Cash flows from financing activities
Proceeds from Series C preferred stock		$ 50,000

Business Description	9 Months Ended
Business Description	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Business Description	1. Business Description G1 Therapeutics, Inc. (the “Company”) is a clinical-stage biopharmaceutical company based in Research Triangle Park, North Carolina dedicated to the discovery and development of novel therapeutics for the treatment of cancer. The Company was incorporated on May 19, 2008 in the state of Delaware. The Company focuses on cyclin-dependent kinases (CDKs), a family of proteins that plays an important role in the growth and proliferation of all human cells. The Company has focused its CDK research on developing potent and selective inhibitors of the kinases CDK4 and CDK6, collectively known as CDK4/6, a validated and promising class of targets for anti-cancer therapeutics. The Company is currently advancing two CDK4/6 inhibitor product candidates in clinical development, trilaciclib and G1T38, each of which has broad therapeutic potential in many forms of cancer and may serve as the backbone of multiple combination regimens. Trilaciclib, the Company’s most advanced clinical-stage candidate, is a potential first-in-class intravenous CDK4/6 inhibitor designed to preserve hematopoietic stem and progenitor cells and enhance immune system function during chemotherapy. Based on compelling response rates and favorable tolerability shown in early-stage trials, trilaciclib is currently being evaluated in four randomized trials: two Phase 1b/2a trials in patients with small cell lung cancer, or SCLC, an additional Phase 2 trial in combination with Tecentriq in SCLC and a Phase 2 in patients with triple-negative breast cancer, or TNBC. G1T38, the Company’s second clinical-stage candidate, is a potential best-in-class oral CDK4/6 inhibitor, to be used in combination with other targeted therapies to treat multiple cancers. A Phase 1 trial of G1T38 in 75 healthy volunteers showed a favorable safety profile, and the Company is conducting a Phase 1/2 trial in ER+, HER2- breast cancer patients in combination with Faslodex® . In November, G1 submitted an Investigational New Drug (IND) application to the U.S. Food and Drug Administration (FDA) to evaluate G1T38, an oral CDK4/6 inhibitor, in combination with Tagrisso® for the treatment of certain types of non-small cell lung cancer. As part of the Company’s strategy to develop wholly-owned proprietary combinations, the Company is advancing the preclinical development of G1T48, a potential first/best-in-class oral selective estrogen receptor degrader, or SERD, which is targeted for the treatment of ER+, HER2- breast cancer. The Company’s financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business. As of September 30, 2017, the Company had an accumulated deficit of $112.1 million. The Company has reported a net loss in all fiscal periods since inception and expects to incur substantial losses in the future to conduct research and development and pre-commercialization activities. These factors raised substantial doubt about its ability to continue as a going concern prior to the Company’s initial public offering (the “IPO”). On May 22, 2017, the Company closed its IPO of 7,781,564 shares of the Company’s common stock at a public offering price of $15.00 per share, including 781,564 shares of common stock issued upon exercise by the underwriters of their option to purchase additional shares. The gross proceeds from the IPO were $116.7 million and net proceeds were $107.1 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. Upon completion of the Company’s IPO, all outstanding preferred stock was automatically converted into an aggregate of 18.9 million shares of common stock. In connection with the IPO, the Board of Directors and the stockholders of the Company approved a one-for-three reverse stock split of the Company’s common stock. The reverse stock split became effective on May 11, 2017. All share and per share amounts in the condensed consolidated financial statements have been retroactively adjusted for all periods presented to give effect to the reverse stock split, including reclassifying an amount equal to the reduction in par value to accumulated deficit. The authorized number of shares of common stock was increased to 120.0 million to be effective as of the date of effectiveness of the Company’s registration statement for its IPO. As of September 30, 2017, the Company had cash and cash equivalents of $118.4 million. The Company expects that its existing cash and cash equivalents will enable it to fund its operating expenses and capital expenditure requirements for at least 18 months. The failure of the Company to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s results of operations and financial condition.

Basis of Presentation and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	2. Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation and Consolidation The accompanying condensed consolidated financial statements of the Company have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”). In the opinion of management, the Company has made all necessary adjustments, which include normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial position and results of operations for the interim periods presented. The year-end condensed balance sheet data was derived from audited financial statements but does not include all disclosures required by U.S. GAAP. The information presented in the condensed consolidated financial statements and related notes as of September 30, 2017, and for the three and nine months ended September 30, 2017 and 2016, is unaudited. The results for the nine months ended September 30, 2017 are not necessarily indicative of the results expected for the full fiscal year or any future period. These interim financial statements should be read in conjunction with the financial statements and notes set forth in the Company’s registration statement on Form S-1 under the Securities Act of 1933, as amended, declared effective by the SEC on May 16, 2017. The December 31, 2016 condensed consolidated balance sheet included herein was derived from the audited financial statements as of that date, but does not include all disclosures, including notes, required by GAAP for complete financial statements. Use of estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and the accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates which include, but are not limited to, estimates related to accrued expenses, accrued external clinical costs, stock-based compensation expense and deferred tax asset valuation allowance. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances. Actual results could differ from those estimates. Income taxes The Company did not record a federal or state income tax benefit for the three and nine months ended September 30, 2017 due to its conclusion that a full valuation allowance is required against the Company’s deferred tax assets. Income taxes are accounted for using the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to temporary differences between the financial statements carrying amounts of assets and liabilities and their respective tax bases, operating loss carryforwards, and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. In accordance with Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) 740, Accounting for Income Taxes, the Company reflects in the financial statements the benefit of positions taken in a previously filed tax return or expected to be taken in a future tax return only when it is considered ‘more-likely-than-not’ that the position taken will be sustained by a taxing authority. As of September 30, 2017 and December 31, 2016, the Company had no unrecognized income tax benefits and correspondingly there is no impact on the Company’s effective income tax rate associated with these items. The Company’s policy for recording interest and penalties relating to uncertain income tax positions is to record them as a component of income tax expense in the accompanying statements of operations. As of September 30, 2017 and December 31, 2016, the Company had no such accruals. Stock-Based Compensation The primary type of stock-based payments utilized by the Company are stock options. The Company accounts for stock-based employee compensation arrangements by measuring the cost of employee services received in exchange for all equity awards granted based on the fair value of the award on the grant date. The fair value of each employee stock option is estimated on the date of grant using an options pricing model. The Company currently uses the Black-Scholes valuation model to estimate the fair value of its share-based payments. The model requires management to make a number of assumptions including expected volatility, expected life, risk-free interest rate and expected dividends. The Company accounts for stock-based non-employee compensation arrangements by recording the expense of such services based on the fair value of the equity instrument as estimated using the Black-Scholes pricing model. The fair value of the equity instrument is charged to operating expense over the term of the service agreement. Recent Accounting Pronouncements In October 2016, the FASB issued ASU No. 2016-17, Consolidation (Topic 810): Interests Held through Related Parties That Are under Common Control, which amends the consolidation guidance on how a reporting entity that is a single decision maker of a variable interest entity should treat indirect interest in the entity held through related parties that are under common control. This guidance is effective for annual periods beginning after December 15, 2016, including interim periods within those annual periods, with early adoption permitted. The Company adopted this ASU on January 1, 2017. The adoption of this standard did not have a material impact on the Company’s financial statements. In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. The FASB issued ASU 2016-09 to simplify several aspects of the accounting for share-based payment transactions, including the income tax consequences. This ASU is effective for annual and interim periods ending after December 15, 2016, with early adoption permitted. This ASU was adopted by the Company for the year ended December 31, 2016. The adoption of this standard did not have a material impact on the Company’s financial statements. In November 2014, the FASB issued ASU No. 2014-16, Determining Whether the Host Contract in a Hybrid Financial Instrument Issued in the Form of a Share Is More Akin to Debt or to Equity. The guidance requires an entity to determine the nature of the host contract by considering all stated and implied substantive terms and features of the hybrid financial instrument, weighing each term and feature on the basis of the relevant facts and circumstances (commonly referred to as the whole-instrument approach). ASU 2014-16 applies to all entities and is effective for annual periods beginning after December 15, 2015, and interim periods thereafter. The ASU was adopted by the Company for the year ended December 31, 2016. Adoption of this standard did not have material impact on the Company’s financial statements. In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern, requiring management to evaluate whether events or conditions could impact an entity’s ability to continue as a going concern for at least one year after the date that the financial statements are issued and to provide disclosures if necessary. Disclosures will be required if conditions give rise to substantial doubt and the type of disclosure will be determined based on whether management’s plans will be able to alleviate the substantial doubt. The ASU was effective for the first annual period ending after December 15, 2016, and for annual periods and interim periods thereafter with early application permitted. The ASU was adopted by the Company for the fourth quarter ended December 31, 2016. Refer to the disclosures in Note 1 for the impact of this adoption. In June 2014, the FASB issued ASU No. 2014-12, Compensation – Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could be Achieved after the Requisite Service Period, which requires the Company to assess share-based awards with performance targets that could be achieved after the requisite service period for potential treatment as performance conditions. Under the ASU, compensation expense is to be recognized when the performance target is deemed probable and should represent the compensation expense attributable to the periods for which service has already been rendered. If the performance target is reached prior to achievement of the service period, the remaining unrecognized compensation cost should be recognized over the remaining service period. The ASU is effective for annual and interim periods beginning after December 15, 2015 with early adoption permitted. This ASU was adopted by the Company for the year ended December 31, 2016. The adoption of this standard did not have a material impact on the Company’s financial statements. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The FASB issued ASU 2016-09 to improve U.S. GAAP by providing guidance on the cash flow statement classification of eight specific areas where there is existing diversity in practice. The FASB expects that the guidance in this ASU will reduce the current and potential future diversity in practice in such areas. This ASU is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company is currently evaluating the impact of the adoption of this ASU on the Company’s financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This guidance revises the accounting related to leases by requiring lessees to recognize a lease liability and a right-of-use asset for all leases. The new lease guidance also simplifies the accounting for sale and leaseback transactions. This ASU is effective for annual reporting periods beginning after December 15, 2018 and early adoption is permitted. The Company is currently evaluating the impact of the adoption of this ASU on the Company’s financial statements. In May 2014, the FASB and the International Accounting Standards Board jointly issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes the revenue recognition requirements in ASC 605 and most industry-specific guidance. The new standard requires that an entity recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods and services. The update also requires additional disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgements and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 is effective for public entities for annual and interim periods within those annual periods beginning after December 15, 2017. The Company is currently evaluating the method of adoption and the potential impact this standard may have on its financial position and results of operations. The future impact of ASU 2014-09 will be dependent on the nature of the Company’s future revenue contracts and arrangements, if any.

Fair Value Measurements

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The Company provides disclosure of financial assets and financial liabilities that are carried at fair value based on the price that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurements may be classified based on the amount of subjectivity associated with the inputs to fair valuation of these assets and liabilities using the following three levels:

Level 1

Inputs are unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

Level 2

Inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability and inputs that are derived principally from or corroborated by observable market data by correlation or other means.

Level 3

Unobservable inputs that reflect the Company’s estimates of the assumptions that market participants would use in pricing the asset or liability. The Company develops these inputs based on the best information available, including its own data.

The carrying amounts of cash, cash equivalents, accounts payable and accrued liabilities approximate fair value because of their short-term nature.

At September 30, 2017 and December 31, 2016 these financials instruments and respective fair values have been classified as follows (in thousands):

	Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant other unobservable inputs (Level 3)		Balance at September 30, 2017
	(unaudited)		(unaudited)		(unaudited)		(unaudited)
Assets
Money market funds	$	102,147	$	—	$	—	$	102,147
Certificates of Deposit		15,152		—		—		15,152
Total assets at fair value:	$	117,299	$	—	$	—	$	117,299
Liabilities:
Warrant Liability	$	—	$	—	$	—	$	—
Total liabilities at fair value:	$	—	$	—	$	—	$	—

	Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant other unobservable inputs (Level 3)		Balance at December 31, 2016
Assets
Money market funds	$	31,730	$	—	$	—	$	31,730
Certificates of Deposit		15,041		—		—		15,041
Total assets at fair value:	$	46,771	$	—	$	—	$	46,771
Liabilities:
Warrant Liability	$	—	$	—	$	167	$	167
Total liabilities at fair value:	$	—	$	—	$	167	$	167

During the three and nine months ended September 30, 2017 and the year ended December 31, 2016, there were no changes in valuation methodology.

- 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

Property and Equipment

9 Months Ended

Sep. 30, 2017

Property Plant And Equipment [Abstract]

Property and Equipment

4. Property and equipment

Property and equipment consists of the following (in thousands):

	September 30, 2017			December 31, 2016
	(unaudited)
Computer equipment	$	104		$	67
Laboratory equipment		268			207
Furniture and fixtures		174			64
Leasehold improvements		121			80
Construction in progress		—			—
Accumulated depreciation		(151	)		(107	)
Property and equipment, net	$	516		$	311

Depreciation expenses relating to property and equipment were $27 and $59 for the three and nine months ended September 30, 2017, respectively, and $18 and $44 for the three and nine months ended September 30, 2016, respectively.

Patent License Agreement	9 Months Ended
Patent License Agreement	Sep. 30, 2017
Patent License Agreement [Abstract]
Patent License Agreement	5. Patent license agreement On November 23, 2016, the Company entered into a license agreement with the Board of Trustees of the University of Illinois (the University), which was amended on March 24, 2017. Pursuant to the license agreement, as amended, the University licensed patent rights to the Company, with rights of sublicense, to make, have made, use, import, sell and offer for sale products covered by certain patent rights owned by the University. The rights licensed to the Company are exclusive, worldwide, non-transferable rights, for all fields of use. Under the terms of the agreement the Company paid a one-time only, non-refundable license issue fee in the amount of $0.5 million which was charged to research and development expense in the fourth quarter of 2016. The Company is also obligated to pay annual maintenance fees to the University. All annual minimum payments are fully creditable against any royalty payments made by the Company. Under the terms of the agreement, the Company must pay the University a royalty percentage on all net sales of products and a share of sublicensing revenues. The University is eligible to receive milestone payments of up to $2.625 million related to the initiation and execution of clinical trials and first commercial sale of a product in multiple countries. The Company is also responsible for all future patent prosecution costs. The term of the license agreement will continue until the later of (i) the expiration of the last valid claim within the patent rights covering the product in such country, (ii) the expiration of market exclusivity in such country and (iii) the 10th anniversary of the first commercial sale in such country. The University may terminate the agreement in the event (i) the Company fails to pay any amount or make any report when required to be made and fails to cure such failure within thirty (30) days after receipt of notice from the University, (ii) is in breach of any provision of the agreement and fails to remedy within forty-five (45) days after receipt of notice, (iii) makes a report to the University under the agreement that is determine to be materially false, (iv) declares insolvency or bankruptcy or (v) takes an action that causes patent rights or technical information to be subject to lien or encumbrance and fails to remedy any such breach with in forty-five (45) days of receipt of notice from the University. The Company may terminate the agreement at any time on written notice to the University at least ninety (90) days prior to the termination date specified in the notice. Upon expiration or termination of the agreement, all rights revert to the University.

Accrued Expenses

9 Months Ended

Sep. 30, 2017

Payables And Accruals [Abstract]

Accrued Expenses

6. Accrued expenses

Accrued expenses are comprised as follows (in thousands):

	September 30, 2017		December 31, 2016
	(unaudited)
Accrued external research and professional fees	$	913	$	295
Accrued external clinical study costs		4,340		1,897
Accrued compensation expense		854		617
Deferred rent		80		44
Accrued expenses	$	6,187	$	2,853

Common Stock and Preferred Stock

9 Months Ended

Sep. 30, 2017

Class Of Stock Disclosures [Abstract]

Common Stock and Preferred Stock

7. Common Stock and Preferred Stock

Common Stock

The Company is authorized to issue 120.0 million shares of common stock. Holders of common stock are entitled to one vote per share. Holders of common stock are entitled to receive dividends, as, if and when declared by the Company’s Board of Directors.

Preferred Stock

Upon completion of the Company’s IPO, all outstanding preferred stock was automatically converted into an aggregate of 18.9 million shares of common stock. The Company is also authorized to issue 5.0 million shares of undesignated preferred stock in one or more series. As of September 30, 2017, no shares of preferred stock were issued or outstanding.

Shares Reserved for Future Issuance

The Company has reserved for future issuance the following number of shares of common stock:

	September 30, 2017		December 31, 2016
	(unaudited)
Conversion of Series C Preferred Stock on a fully-diluted basis		—		5,609,398
Conversion of Series B Preferred Stock on a fully-diluted basis		—		7,642,734
Conversion of Series A Preferred Stock on a fully-diluted basis		—		4,998,895
Conversion of Series 1 Preferred Stock on a fully-diluted basis		—		682,026
Common stock warrants issued with promissory notes		—		16,666
Other common stock warrants		—		3,466
Series 1 Preferred Stock warrants issued with promissory notes		—		21,978
Common stock options outstanding		3,898,506		3,690,058
Options available for grant under Equity Incentive Plans		1,721,665		176,919
		5,620,171		22,842,140

Stock-based Compensation

9 Months Ended

Sep. 30, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-based Compensation

8. Stock-based Compensation

2011 Equity Incentive Plan

In March 2011, the Company adopted the 2011 Equity Incentive Plan (the “2011 Plan”). The 2011 Plan provided for the direct award or sale of the Company’s common stock and for the grant of stock options to employees, directors, officers, consultants and advisors of the Company. The 2011 Plan was subsequently amended in August 2012, October 2013, February 2015, December 2015, April 2016 and November 2016 to allow for the issuance of additional shares of common stock. In connection with the adoption of the 2017 Plan (as defined below), the 2011 Plan was terminated and no further awards will be made under the 2011 Plan.

2017 Equity Incentive Plan

In May 2017, the Company adopted the 2017 Equity Incentive Plan (the “2017 Plan”). The 2017 Plan provided for the direct award or sale of the Company’s common stock and for the grant of up to 1,932,000 stock options to employees, directors, officers, consultants and advisors of the Company. The 2017 Plan provides for the grant of incentive stock options, non-statutory stock options or restricted stock.

Under both the 2011 Plan and the 2017 Plan, options to purchase the Company’s common stock may be granted at a price no less than the fair market value of a share of common stock on the date of grant. The fair value shall be the closing sales price for a share as quoted on any established securities exchange for such grant date or the last preceding date for which such quotation exists. Vesting terms of options issued are determined by the board of directors or compensation committee of the board. The Company’s stock options vest based on terms in the stock option agreements. Stock options have a maximum term of ten years.

As of September 30, 2017, there were a total of 1,721,665 shares of common stock available for future issuance under the 2017 Plan.

Stock Option Expense

The Company recognizes compensation costs related to stock options granted to employees based on the estimated fair value of the awards on the date of grant, net of estimated forfeitures. The grant date fair value of the stock-based awards is generally recognized on a straight-line basis over the requisite service period, which is generally the vesting period of the respective awards. Share-based awards granted to non-employee directors as compensation for serving on the Company’s Board of Directors are accounted for in the same manner as employee share based compensation awards.

During the three and nine months ended September 30, 2017, the Company recorded employee share-based compensation expense of $501 and $1,175, respectively. During the three and nine months ended September 30, 2016, the Company recorded employee share-based compensation expense of $276 and $610, respectively.

The Company recognizes compensation costs related to stock options granted to non-employees based on the estimated fair value of the awards on the date of grant in the same manner as employees; however, the fair value of the stock options granted to non-employees is re-measured each reporting period until the service is complete, and the resulting increase or decrease in value, if any, is recognized as expense or income, respectively, during the period the related services are rendered.

During the three and nine months ended September 30, 2017, the Company recorded non-employee share-based compensation expense of $539 and $1,182, respectively. During the three and nine months ended September 30, 2016, the Company recorded non-employee share-based compensation expense of $93 and $298, respectively.

The Company calculates the fair value of stock options using the Black-Scholes option pricing model. The Black-Scholes option-pricing model requires the use of subjective assumptions, including the expected volatility of the Company’s common stock, the assumed dividend yield, the expected term of the Company’s stock options and the fair value of the underlying common stock on the date of grant.

Stock options— Black-Scholes inputs

The fair value of stock options was estimated using the following weighted-average assumptions for the three and nine months ended September 30, 2017 and September 30, 2016:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	(unaudited)				(unaudited)
Expected volatility	74.6 - 75.1%		78.2 - 78.4%		74.2 - 79.3%		74.7 - 78.4%
Weighted-average risk free rate	1.9 - 2.0%			1.3%	1.9 - 2.1%		1.2 - 1.4%
Dividend yield		—%		—%		—%		—%
Expected term (in years)	5.94		6.05		5.98		6.03

The table below summarizes the stock-based compensation expense recognized in the Company’s statement of operations by classification (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	(unaudited)				(unaudited)
Research and development	$	792	$	222	$	1,796	$	576
General and administrative		248		147		561		332
Total stock-based compensation expense	$	1,040	$	369	$	2,357	$	908

Stock Option Activity

Stock option activity for the nine months ended September 30, 2017 is as follows:

						Weighted average
				Weighted		Remaining
				average		contractual		Aggregate
	Options			exercise		for		intrinsic
	outstanding			price		life (Years)		value
								(in thousands)
Balance as of December 31, 2016		3,690,058		$	2.13		8.4	$	17,463
Cancelled		(31,665	)	$	2.01
Granted		361,997			12.68
Exercised		(121,884	)		1.46
Balance as of September 30, 2017		3,898,506		$	3.14		7.9	$	84,796
Exercisable at December 31, 2016		1,396,191			0.84		7.8	$	8,410
Vested at December 31, 2016 and expected to vest		3,690,058			2.13		8.4	$	17,463
Exercisable at September 30, 2017		2,037,649			1.51		7.4	$	47,634
Vested at September 30, 2017 and expected to vest		3,898,506			3.14		7.9	$	84,796

Net Loss Per Common Share

9 Months Ended

Sep. 30, 2017

Earnings Per Share [Abstract]

Net Loss Per Common Share

9. Net loss per common share

Net loss per common share

Basic net loss per common share is computed using the weighted average number of common shares outstanding during the period including nominal issuances of common stock warrants. Diluted net loss per common share is computed using the sum of the weighted average number of common shares outstanding during the period and, if dilutive, the weighted average number of potential shares of common stock, including the assumed exercise of stock options, stock warrants and unvested restricted common stock. For the three months ended September 30, 2017 and 2016 and for the nine months ended September 30, 2017 and 2016, the following potentially dilutive securities have been excluded from the computations of diluted weighted-average shares outstanding because the effect would be anti-dilutive:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	(unaudited)				(unaudited)
Stock options issued and outstanding		3,894,192		3,544,800		3,805,419		3,085,370
Stock warrants		—		25,444		15,223		25,444
		3,894,192		3,570,244		3,820,642		3,110,814

Amounts in the table above reflect the common stock equivalents of the noted instruments.

The following table summarizes the calculation of the basic and diluted net loss per common share (in thousands, except share and per share amounts):

	Three Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
	(unaudited)						(unaudited)
Numerator:
Loss from operations	$	(15,601	)	$	(6,557	)	$	(43,140	)	$	(19,890	)
Less: accretion of redeemable convertible preferred stock		—			(1,205	)		(4,757	)		(3,200	)
Net loss attributable to common stockholders	$	(15,601	)	$	(7,762	)	$	(47,897	)	$	(23,090	)
Denominator:
Weighted-average basic and diluted common shares		28,318,656			1,490,552			14,772,621			1,484,713
Basic and diluted net loss per common share	$	(0.55	)	$	(5.21	)	$	(3.24	)	$	(15.55	)

Related Party Transactions	9 Months Ended
Related Party Transactions	Sep. 30, 2017
Related Party Transactions [Abstract]
Related Party Transactions	10. Related party transactions Two co-founders and shareholders of the Company had consulting agreements with the Company relating to their continued development work through June 30, 2017. The Company renewed its consulting agreement with one of these founders through June 30, 2019. Combined consulting fees paid to both founders were approximately $5 and $27 for the three months ended September 30, 2017 and September 30, 2016, respectively, and $59 and $81 for the nine months ended September 30, 2017 and September 30, 2016, respectively under the agreements. The Company paid approximately $2 and $3 to the Chairman of the Board of Directors for consulting services during the three months ended September 30, 2017 and September 30, 2016, respectively and $9 and $12 for the nine months ended September 30, 2017 and September 30, 2016, respectively.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying condensed consolidated financial statements of the Company have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”). In the opinion of management, the Company has made all necessary adjustments, which include normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial position and results of operations for the interim periods presented. The year-end condensed balance sheet data was derived from audited financial statements but does not include all disclosures required by U.S. GAAP. The information presented in the condensed consolidated financial statements and related notes as of September 30, 2017, and for the three and nine months ended September 30, 2017 and 2016, is unaudited. The results for the nine months ended September 30, 2017 are not necessarily indicative of the results expected for the full fiscal year or any future period. These interim financial statements should be read in conjunction with the financial statements and notes set forth in the Company’s registration statement on Form S-1 under the Securities Act of 1933, as amended, declared effective by the SEC on May 16, 2017. The December 31, 2016 condensed consolidated balance sheet included herein was derived from the audited financial statements as of that date, but does not include all disclosures, including notes, required by GAAP for complete financial statements.
Use of Estimates	Use of estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and the accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates which include, but are not limited to, estimates related to accrued expenses, accrued external clinical costs, stock-based compensation expense and deferred tax asset valuation allowance. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Income Taxes	Income taxes The Company did not record a federal or state income tax benefit for the three and nine months ended September 30, 2017 due to its conclusion that a full valuation allowance is required against the Company’s deferred tax assets. Income taxes are accounted for using the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to temporary differences between the financial statements carrying amounts of assets and liabilities and their respective tax bases, operating loss carryforwards, and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. In accordance with Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) 740, Accounting for Income Taxes, the Company reflects in the financial statements the benefit of positions taken in a previously filed tax return or expected to be taken in a future tax return only when it is considered ‘more-likely-than-not’ that the position taken will be sustained by a taxing authority. As of September 30, 2017 and December 31, 2016, the Company had no unrecognized income tax benefits and correspondingly there is no impact on the Company’s effective income tax rate associated with these items. The Company’s policy for recording interest and penalties relating to uncertain income tax positions is to record them as a component of income tax expense in the accompanying statements of operations. As of September 30, 2017 and December 31, 2016, the Company had no such accruals.
Stock-Based Compensation	Stock-Based Compensation The primary type of stock-based payments utilized by the Company are stock options. The Company accounts for stock-based employee compensation arrangements by measuring the cost of employee services received in exchange for all equity awards granted based on the fair value of the award on the grant date. The fair value of each employee stock option is estimated on the date of grant using an options pricing model. The Company currently uses the Black-Scholes valuation model to estimate the fair value of its share-based payments. The model requires management to make a number of assumptions including expected volatility, expected life, risk-free interest rate and expected dividends. The Company accounts for stock-based non-employee compensation arrangements by recording the expense of such services based on the fair value of the equity instrument as estimated using the Black-Scholes pricing model. The fair value of the equity instrument is charged to operating expense over the term of the service agreement.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In October 2016, the FASB issued ASU No. 2016-17, Consolidation (Topic 810): Interests Held through Related Parties That Are under Common Control, which amends the consolidation guidance on how a reporting entity that is a single decision maker of a variable interest entity should treat indirect interest in the entity held through related parties that are under common control. This guidance is effective for annual periods beginning after December 15, 2016, including interim periods within those annual periods, with early adoption permitted. The Company adopted this ASU on January 1, 2017. The adoption of this standard did not have a material impact on the Company’s financial statements. In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. The FASB issued ASU 2016-09 to simplify several aspects of the accounting for share-based payment transactions, including the income tax consequences. This ASU is effective for annual and interim periods ending after December 15, 2016, with early adoption permitted. This ASU was adopted by the Company for the year ended December 31, 2016. The adoption of this standard did not have a material impact on the Company’s financial statements. In November 2014, the FASB issued ASU No. 2014-16, Determining Whether the Host Contract in a Hybrid Financial Instrument Issued in the Form of a Share Is More Akin to Debt or to Equity. The guidance requires an entity to determine the nature of the host contract by considering all stated and implied substantive terms and features of the hybrid financial instrument, weighing each term and feature on the basis of the relevant facts and circumstances (commonly referred to as the whole-instrument approach). ASU 2014-16 applies to all entities and is effective for annual periods beginning after December 15, 2015, and interim periods thereafter. The ASU was adopted by the Company for the year ended December 31, 2016. Adoption of this standard did not have material impact on the Company’s financial statements. In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern, requiring management to evaluate whether events or conditions could impact an entity’s ability to continue as a going concern for at least one year after the date that the financial statements are issued and to provide disclosures if necessary. Disclosures will be required if conditions give rise to substantial doubt and the type of disclosure will be determined based on whether management’s plans will be able to alleviate the substantial doubt. The ASU was effective for the first annual period ending after December 15, 2016, and for annual periods and interim periods thereafter with early application permitted. The ASU was adopted by the Company for the fourth quarter ended December 31, 2016. Refer to the disclosures in Note 1 for the impact of this adoption. In June 2014, the FASB issued ASU No. 2014-12, Compensation – Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could be Achieved after the Requisite Service Period, which requires the Company to assess share-based awards with performance targets that could be achieved after the requisite service period for potential treatment as performance conditions. Under the ASU, compensation expense is to be recognized when the performance target is deemed probable and should represent the compensation expense attributable to the periods for which service has already been rendered. If the performance target is reached prior to achievement of the service period, the remaining unrecognized compensation cost should be recognized over the remaining service period. The ASU is effective for annual and interim periods beginning after December 15, 2015 with early adoption permitted. This ASU was adopted by the Company for the year ended December 31, 2016. The adoption of this standard did not have a material impact on the Company’s financial statements. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The FASB issued ASU 2016-09 to improve U.S. GAAP by providing guidance on the cash flow statement classification of eight specific areas where there is existing diversity in practice. The FASB expects that the guidance in this ASU will reduce the current and potential future diversity in practice in such areas. This ASU is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company is currently evaluating the impact of the adoption of this ASU on the Company’s financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This guidance revises the accounting related to leases by requiring lessees to recognize a lease liability and a right-of-use asset for all leases. The new lease guidance also simplifies the accounting for sale and leaseback transactions. This ASU is effective for annual reporting periods beginning after December 15, 2018 and early adoption is permitted. The Company is currently evaluating the impact of the adoption of this ASU on the Company’s financial statements. In May 2014, the FASB and the International Accounting Standards Board jointly issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes the revenue recognition requirements in ASC 605 and most industry-specific guidance. The new standard requires that an entity recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods and services. The update also requires additional disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgements and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 is effective for public entities for annual and interim periods within those annual periods beginning after December 15, 2017. The Company is currently evaluating the method of adoption and the potential impact this standard may have on its financial position and results of operations. The future impact of ASU 2014-09 will be dependent on the nature of the Company’s future revenue contracts and arrangements, if any.

- Definition

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.

+ References + Details

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Summary of Financials Instruments and Respective Fair Values

At September 30, 2017 and December 31, 2016 these financials instruments and respective fair values have been classified as follows (in thousands):

	Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant other unobservable inputs (Level 3)		Balance at September 30, 2017
	(unaudited)		(unaudited)		(unaudited)		(unaudited)
Assets
Money market funds	$	102,147	$	—	$	—	$	102,147
Certificates of Deposit		15,152		—		—		15,152
Total assets at fair value:	$	117,299	$	—	$	—	$	117,299
Liabilities:
Warrant Liability	$	—	$	—	$	—	$	—
Total liabilities at fair value:	$	—	$	—	$	—	$	—

	Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant other unobservable inputs (Level 3)		Balance at December 31, 2016
Assets
Money market funds	$	31,730	$	—	$	—	$	31,730
Certificates of Deposit		15,041		—		—		15,041
Total assets at fair value:	$	46,771	$	—	$	—	$	46,771
Liabilities:
Warrant Liability	$	—	$	—	$	167	$	167
Total liabilities at fair value:	$	—	$	—	$	167	$	167

Property and Equipment (Tables)

9 Months Ended

Sep. 30, 2017

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consists of the following (in thousands):

	September 30, 2017			December 31, 2016
	(unaudited)
Computer equipment	$	104		$	67
Laboratory equipment		268			207
Furniture and fixtures		174			64
Leasehold improvements		121			80
Construction in progress		—			—
Accumulated depreciation		(151	)		(107	)
Property and equipment, net	$	516		$	311

Accrued expenses (Tables)

9 Months Ended

Sep. 30, 2017

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses are comprised as follows (in thousands):

	September 30, 2017		December 31, 2016
	(unaudited)
Accrued external research and professional fees	$	913	$	295
Accrued external clinical study costs		4,340		1,897
Accrued compensation expense		854		617
Deferred rent		80		44
Accrued expenses	$	6,187	$	2,853

Common Stock and Preferred Stock (Tables)

9 Months Ended

Sep. 30, 2017

Class Of Stock Disclosures [Abstract]

Summary of common stock shares reserved for future issuance

The Company has reserved for future issuance the following number of shares of common stock:

	September 30, 2017		December 31, 2016
	(unaudited)
Conversion of Series C Preferred Stock on a fully-diluted basis		—		5,609,398
Conversion of Series B Preferred Stock on a fully-diluted basis		—		7,642,734
Conversion of Series A Preferred Stock on a fully-diluted basis		—		4,998,895
Conversion of Series 1 Preferred Stock on a fully-diluted basis		—		682,026
Common stock warrants issued with promissory notes		—		16,666
Other common stock warrants		—		3,466
Series 1 Preferred Stock warrants issued with promissory notes		—		21,978
Common stock options outstanding		3,898,506		3,690,058
Options available for grant under Equity Incentive Plans		1,721,665		176,919
		5,620,171		22,842,140

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Paragraph 1
-Subparagraph (SX 210.4-08(d))
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Subparagraph (SX 210.5-02(29))
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-Name Accounting Standards Codification
-Topic 505
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-SubTopic 10
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-Paragraph 1
-Subparagraph (SX 210.5-02(28))
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65888546&loc=d3e21300-112643

Reference 10: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-SubTopic 10
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-Subparagraph (SX 210.5-02(27))
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+ Details

Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2017

Summary of Stock Option Activity

Stock Option Activity

Stock option activity for the nine months ended September 30, 2017 is as follows:

						Weighted average
				Weighted		Remaining
				average		contractual		Aggregate
	Options			exercise		for		intrinsic
	outstanding			price		life (Years)		value
								(in thousands)
Balance as of December 31, 2016		3,690,058		$	2.13		8.4	$	17,463
Cancelled		(31,665	)	$	2.01
Granted		361,997			12.68
Exercised		(121,884	)		1.46
Balance as of September 30, 2017		3,898,506		$	3.14		7.9	$	84,796
Exercisable at December 31, 2016		1,396,191			0.84		7.8	$	8,410
Vested at December 31, 2016 and expected to vest		3,690,058			2.13		8.4	$	17,463
Exercisable at September 30, 2017		2,037,649			1.51		7.4	$	47,634
Vested at September 30, 2017 and expected to vest		3,898,506			3.14		7.9	$	84,796

Employee and Non-employee Stock Options

Summary of Fair Value of Stock Options Granted Using Black-Scholes Options Pricing Model

The fair value of stock options was estimated using the following weighted-average assumptions for the three and nine months ended September 30, 2017 and September 30, 2016:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	(unaudited)				(unaudited)
Expected volatility	74.6 - 75.1%		78.2 - 78.4%		74.2 - 79.3%		74.7 - 78.4%
Weighted-average risk free rate	1.9 - 2.0%			1.3%	1.9 - 2.1%		1.2 - 1.4%
Dividend yield		—%		—%		—%		—%
Expected term (in years)	5.94		6.05		5.98		6.03

Summary of Stock-Based Compensation Expense Recognized in Statement of Operations by Classification

The table below summarizes the stock-based compensation expense recognized in the Company’s statement of operations by classification (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	(unaudited)				(unaudited)
Research and development	$	792	$	222	$	1,796	$	576
General and administrative		248		147		561		332
Total stock-based compensation expense	$	1,040	$	369	$	2,357	$	908

Net Loss Per Common Share (Tables)

9 Months Ended

Sep. 30, 2017

Earnings Per Share [Abstract]

Schedule of Potentially Dilutive Securities Excluded from Computations of Diluted Weighted-average Shares Outstanding

For the three months ended September 30, 2017 and 2016 and for the nine months ended September 30, 2017 and 2016, the following potentially dilutive securities have been excluded from the computations of diluted weighted-average shares outstanding because the effect would be anti-dilutive:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	(unaudited)				(unaudited)
Stock options issued and outstanding		3,894,192		3,544,800		3,805,419		3,085,370
Stock warrants		—		25,444		15,223		25,444
		3,894,192		3,570,244		3,820,642		3,110,814

Summary of Calculation of Basic and Diluted Net Loss Per Common Shares

The following table summarizes the calculation of the basic and diluted net loss per common share (in thousands, except share and per share amounts):

	Three Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
	(unaudited)						(unaudited)
Numerator:
Loss from operations	$	(15,601	)	$	(6,557	)	$	(43,140	)	$	(19,890	)
Less: accretion of redeemable convertible preferred stock		—			(1,205	)		(4,757	)		(3,200	)
Net loss attributable to common stockholders	$	(15,601	)	$	(7,762	)	$	(47,897	)	$	(23,090	)
Denominator:
Weighted-average basic and diluted common shares		28,318,656			1,490,552			14,772,621			1,484,713
Basic and diluted net loss per common share	$	(0.55	)	$	(5.21	)	$	(3.24	)	$	(15.55	)

Business Description - Additional Information (Details) $ / shares in Units, $ in Thousands		9 Months Ended
	May 22, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Description Of Business [Line Items]
Accumulated deficit		$ 112,137	$ 64,985
Proceeds from initial public offering, net of underwriting fees and commissions		$ 108,503
Reverse stock split description		In connection with the IPO, the Board of Directors and the stockholders of the Company approved a one-for-three reverse stock split of the Company’s common stock.
Reverse stock split ratio		0.33
Reverse stock split effective date		May 11, 2017
Common stock, shares authorized \| shares		120,000,000	73,000,000
Cash and cash equivalents		$ 118,380	$ 47,305	$ 56,554	$ 22,938
Minimum
Description Of Business [Line Items]
Expected period to fund operations by existing cash resources		18 months
IPO
Description Of Business [Line Items]
Common stock, shares issued \| shares	7,781,564
Common stock, price per share \| $ / shares	$ 15.00
Gross proceeds from issuance of common stock	$ 116,700
Proceeds from initial public offering, net of underwriting fees and commissions	$ 107,100
IPO \| Convertible Preferred Stock
Description Of Business [Line Items]
Conversion of outstanding preferred stock to common stock \| shares	18,900,000	18,900,000
Underwriters Option to Purchase
Description Of Business [Line Items]
Common stock, shares issued \| shares	781,564

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Unrecognized income tax benefits	$ 0	$ 0
Accrued income taxes	$ 0	$ 0

Fair Value Measurements - Summary of Financials Instruments and Respective Fair Values (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets
Assets at fair value	$ 117,299	$ 46,771
Liabilities:
Liabilities at fair value		167
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Assets at fair value	117,299	46,771
Significant Other Unobservable Inputs (Level 3)
Liabilities:
Liabilities at fair value		167
Money Market Funds
Assets
Assets at fair value	102,147	31,730
Money Market Funds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Assets at fair value	102,147	31,730
Certificates of Deposit
Assets
Assets at fair value	15,152	15,041
Certificates of Deposit \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Assets at fair value	$ 15,152	15,041
Warrant Liability
Liabilities:
Liabilities at fair value		167
Warrant Liability \| Significant Other Unobservable Inputs (Level 3)
Liabilities:
Liabilities at fair value		$ 167

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Accumulated depreciation	$ (151)	$ (107)
Property and equipment, net	516	311
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	104	67
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	268	207
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	174	64
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 121	$ 80

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Property Plant And Equipment [Abstract]
Depreciation expenses relating to property and equipment	$ 27	$ 18	$ 59	$ 44

Patent License Agreement - Additional Information (Details) - University - USD ($)	3 Months Ended	9 Months Ended
	Dec. 31, 2016	Sep. 30, 2017
Patent License Agreement [Line Items]
License agreement date		Nov. 23, 2016
License agreement amendment date		Mar. 24, 2017
Non-refundable license issue fee	$ 500,000
Term of license agreement description		The term of the license agreement will continue until the later of (i) the expiration of the last valid claim within the patent rights covering the product in such country, (ii) the expiration of market exclusivity in such country and (iii) the 10th anniversary of the first commercial sale in such country. The University may terminate the agreement in the event (i) the Company fails to pay any amount or make any report when required to be made and fails to cure such failure within thirty (30) days after receipt of notice from the University, (ii) is in breach of any provision of the agreement and fails to remedy within forty-five (45) days after receipt of notice, (iii) makes a report to the University under the agreement that is determine to be materially false, (iv) declares insolvency or bankruptcy or (v) takes an action that causes patent rights or technical information to be subject to lien or encumbrance and fails to remedy any such breach with in forty-five (45) days of receipt of notice from the University. The Company may terminate the agreement at any time on written notice to the University at least ninety (90) days prior to the termination date specified in the notice. Upon expiration or termination of the agreement, all rights revert to the University.
License agreement termination notice period		90 days
Maximum [Member]
Patent License Agreement [Line Items]
Milestone payments		$ 2,625,000

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued external research and professional fees	$ 913	$ 295
Accrued external clinical study costs	4,340	1,897
Accrued compensation expense	854	617
Deferred rent	80	44
Accrued expenses	$ 6,187	$ 2,853

Common Stock and Preferred Stock - Additional Information (Details) - shares		9 Months Ended
	May 22, 2017	Sep. 30, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Common stock, shares authorized		120,000,000	73,000,000
Common stock, voting rights		Holders of common stock are entitled to one vote per share.
Undesignated preferred stock, shares authorized to issue		5,000,000
Preferred stock, shares issued		0
Preferred stock, shares outstanding		0
IPO \| Convertible Preferred Stock
Class Of Stock [Line Items]
Conversion of outstanding preferred stock to common stock	18,900,000	18,900,000

Common Stock and Preferred Stock - Summary of common stock shares reserved for future issuance (Details) - shares	Sep. 30, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance	5,620,171	22,842,140
Conversion of Series C Preferred Stock On A Fully-Diluted Basis
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance		5,609,398
Conversion of Series B Preferred Stock On A Fully-Diluted Basis
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance		7,642,734
Conversion of Series A Preferred Stock On A Fully-Diluted Basis
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance		4,998,895
Conversion of Series 1 Preferred Stock On A Fully-Diluted Basis
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance		682,026
Common Stock Warrants Issued With Promissory Notes
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance		16,666
Other Common Stock Warrants
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance		3,466
Series 1 Preferred Stock Warrants Issued With Promissory Notes
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance		21,978
Common Stock Options Outstanding
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance	3,898,506	3,690,058
Options Available For Grant Under Equity Incentive Plan
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance	1,721,665	176,919

Stock-based Compensation - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	May 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense			$ 2,357	$ 908
Employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 501	$ 276	1,175	610
Non-employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 539	$ 93	$ 1,182	$ 298
2017 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares approved for grant under equity incentive plan					1,932,000
Common stock available for future issuance	1,721,665		1,721,665

Stock-based Compensation - Fair Value of Stock Options Granted Using Black-Scholes Options Pricing Model (Details) - Employee and Non-employee Stock Options	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	74.60%	78.20%	74.20%	74.70%
Expected volatility, maximum	75.10%	78.40%	79.30%	78.40%
Weighted-average risk free rate		1.30%
Weighted-average risk free rate, minimum	1.90%		1.90%	1.20%
Weighted-average risk free rate, maximum	2.00%		2.10%	1.40%
Expected term (in years)	5 years 11 months 8 days	6 years 18 days	5 years 11 months 23 days	6 years 11 days

Stock-based Compensation - Summary of Stock-Based Compensation Expense Recognized in Statement of Operations by Classification (Details) - Employee and Non-employee Stock Options - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,040	$ 369	$ 2,357	$ 908
Research and development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	792	222	1,796	576
General and administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 248	$ 147	$ 561	$ 332

Stock-based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Options outstanding
Beginning balance	3,690,058
Cancelled	(31,665)
Granted	361,997
Exercised	(121,884)
Ending balance	3,898,506	3,690,058
Exercisable	2,037,649	1,396,191
Vested and expected to vest	3,898,506	3,690,058
Weighted average exercise price
Beginning balance	$ 2.13
Cancelled	2.01
Granted	12.68
Exercised	1.46
Ending balance	3.14	$ 2.13
Exercisable	1.51	0.84
Vested and expected to vest	$ 3.14	$ 2.13
Weighted average, Remaining contractual for life (Years)
Balance	7 years 10 months 25 days	8 years 4 months 24 days
Exercisable	7 years 4 months 24 days	7 years 9 months 18 days
Vested and expected to vest	7 years 10 months 25 days	8 years 4 months 24 days
Weighted average, Aggregate intrinsic value
Balance	$ 84,796	$ 17,463
Exercisable	47,634	8,410
Vested and expected to vest	$ 84,796	$ 17,463

Net Loss Per Common Share - Schedule of Potentially Dilutive Securities Excluded from Computations of Diluted Weighted-average Shares Outstanding (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computations of diluted weighted-average shares outstanding	3,894,192	3,570,244	3,820,642	3,110,814
Stock Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computations of diluted weighted-average shares outstanding	3,894,192	3,544,800	3,805,419	3,085,370
Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computations of diluted weighted-average shares outstanding		25,444	15,223	25,444

Net Loss Per Common Share - Summary of Calculation of Basic and Diluted Net Loss Per Common Shares (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Loss from operations	$ (15,601)	$ (6,557)	$ (43,140)	$ (19,890)
Less: accretion of redeemable convertible preferred stock		(1,205)	(4,757)	(3,200)
Net loss attributable to common stockholders	$ (15,601)	$ (7,762)	$ (47,897)	$ (23,090)
Denominator:
Weighted-average basic and diluted common shares	28,318,656	1,490,552	14,772,621	1,484,713
Basic and diluted net loss per common share	$ (0.55)	$ (5.21)	$ (3.24)	$ (15.55)

Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Founders
Related Party Transaction [Line Items]
Consulting fees	$ 5	$ 27	$ 59	$ 81
One of the Founders
Related Party Transaction [Line Items]
Consulting agreement renewed expiry date			Jun. 30, 2019
Consulting Services \| Chairman of the Board of Directors
Related Party Transaction [Line Items]
Consulting fees	$ 2	$ 3	$ 9	$ 12