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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	Apr. 30, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Trading Symbol	GTHX
Entity Registrant Name	G1 THERAPEUTICS, INC.
Entity Central Index Key	0001560241
Current Fiscal Year End Date	--12-31
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		37,737,260
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-38096
Entity Address, Address Line One	700 Park Offices Drive
Entity Address, Address Line Two	Suite 200
Entity Address, City or Town	Research Triangle Park
Entity Address, State or Province	NC
Entity Address, Postal Zip Code	27709
City Area Code	919
Local Phone Number	213-9835
Entity Tax Identification Number	26-3648180
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes

Condensed Balance Sheets (unaudited) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 242,402	$ 269,208
Restricted cash	63	63
Prepaid expenses and other current assets	1,124	1,732
Total current assets	243,589	271,003
Property and equipment, net	3,371	3,538
Restricted cash	437	437
Operating lease assets	9,117	9,853
Total assets	256,514	284,831
Current liabilities
Accounts payable	4,703	3,684
Accrued expenses	12,682	15,403
Other current liabilities	1,063	682
Total current liabilities	18,448	19,769
Operating lease liabilities	8,616	9,535
Total liabilities	27,064	29,304
Stockholders’ equity
Common stock, $0.0001 par value, 120,000,000 shares authorized as of March 31, 2020 and December 31, 2019, respectively; 37,763,926 and 37,638,260 shares issued as of March 31, 2020 and December 31, 2019, respectively; 37,737,260 and 37,611,594 shares outstanding as of March 31, 2020 and December 31, 2019, respectively	4	4
Treasury stock, 26,666 shares	(8)	(8)
Additional paid-in capital	597,330	592,384
Accumulated deficit	(367,876)	(336,853)
Total stockholders’ equity	229,450	255,527
Total liabilities and stockholders' equity	$ 256,514	$ 284,831

Condensed Balance Sheets (Parenthetical) (unaudited) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares, issued	37,763,926	37,638,260
Common stock, shares, outstanding	37,737,260	37,611,594
Treasury stock, shares	26,666	26,666

Condensed Statements of Operations (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating expenses
Research and development	$ 20,434	$ 18,080
General and administrative	11,387	7,801
Total operating expenses	31,821	25,881
Operating loss	(31,821)	(25,881)
Other income (expense)
Other income	798	1,929
Total other income, net	798	1,929
Net loss	(31,023)	(23,952)
Net loss attributable to common stockholders	$ (31,023)	$ (23,952)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.82)	$ (0.64)
Weighted average common shares outstanding, basic and diluted	37,659,722	37,396,980

Condensed Statements of Stockholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2018	$ 358,820	$ 4	$ (8)	$ 573,230	$ (214,406)
Balance (in shares) at Dec. 31, 2018		37,268,792	(26,666)
Exercise of common stock options	269			269
Exercise of common stock options (in shares)		218,890
Stock-based compensation	3,804			3,804
Net loss during quarter	(23,952)				(23,952)
Balance at Mar. 31, 2019	338,941	$ 4	$ (8)	577,303	(238,358)
Balance (in shares) at Mar. 31, 2019		37,487,682	(26,666)
Balance at Dec. 31, 2019	255,527	$ 4	$ (8)	592,384	(336,853)
Balance (in shares) at Dec. 31, 2019		37,638,260	(26,666)
Exercise of common stock options	$ 219			219
Exercise of common stock options (in shares)	125,666	125,666
Stock-based compensation	$ 4,727			4,727
Net loss during quarter	(31,023)				(31,023)
Balance at Mar. 31, 2020	$ 229,450	$ 4	$ (8)	$ 597,330	$ (367,876)
Balance (in shares) at Mar. 31, 2020		37,763,926	(26,666)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Condensed Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net loss	$ (31,023)	$ (23,952)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	159	64
Stock-based compensation	4,727	3,804
Loss on disposal of fixed assets	8
Change in operating assets and liabilities
Prepaid expenses and other assets	1,371	156
Accounts payable	992	(631)
Accrued expenses and other liabilities	(3,259)	(987)
Net cash used in operating activities	(27,025)	(21,546)
Cash flows from investing activities
Purchases of property and equipment		(216)
Net cash used in investing activities		(216)
Cash flows from financing activities
Proceeds from stock options and warrants exercised	219	269
Net cash provided by financing activities	219	269
Net change in cash and cash equivalents	(26,806)	(21,493)
Cash and cash equivalents and restricted cash
Beginning of period	269,708	369,290
End of period	242,902	347,797
Non-cash investing and financing activities
Upfront project costs and other current assets in accounts payable	$ 27	315
Purchases of equipment in accounts payable and accrued expenses		$ 54

Fair Value Measurements

3 Months Ended

Mar. 31, 2020

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 March 31, 2020 and December 31, 2019 these financial 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 March 31, 2020

Assets
Money market funds	$	225,886	$	—	$	—	$	225,886
Certificates of Deposit		15,942		—		—		15,942
Total assets at fair value:	$	241,828	$	—	$	—	$	241,828

	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, 2019
Assets
Money market funds	$	252,563	$	—	$	—	$	252,563
Certificates of Deposit		15,873		—		—		15,873
Total assets at fair value:	$	268,436	$	—	$	—	$	268,436

During the three months ended March 31, 2020 and the year ended December 31, 2019, 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

3 Months Ended

Mar. 31, 2020

Property Plant And Equipment [Abstract]

Property and Equipment

4. Property and equipment

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

	March 31, 2020			December 31, 2019

Computer equipment	$	330		$	332
Laboratory equipment		865			871
Furniture and fixtures		1,071			1,071
Leasehold improvements		1,941			1,941
Accumulated depreciation		(836	)		(677	)
Property and equipment, net	$	3,371		$	3,538

Depreciation expense relating to property and equipment was $159 thousand for the three months ended March 31, 2020 and $64 thousand for the three months ended March 31, 2019.

Patent License Agreement

3 Months Ended

Mar. 31, 2020

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 royalty percentage on all net sales of products and a share of sublicensing revenues. In addition, the University is eligible to receive milestone payments of up to $2.6 million related to the initiation and execution of clinical trials and the first commercial sale of a product in another country. To date, the Company has made milestone payments totaling $0.6 million, of which $0 was incurred during the first quarter of 2020. The Company will be responsible for any future patent prosecution costs that may arise.

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 determined 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 within 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

3 Months Ended

Mar. 31, 2020

Payables And Accruals [Abstract]

Accrued Expenses

6. Accrued expenses

Accrued expenses are comprised as follows (in thousands):

	March 31, 2020		December 31, 2019

Accrued external research	$	2,216	$	2,737
Accrued professional fees and other		1,914		1,487
Accrued external clinical study costs		7,596		7,996
Accrued compensation expense		956		3,183
Accrued expenses	$	12,682	$	15,403

Stockholders' Equity

3 Months Ended

Mar. 31, 2020

Equity [Abstract]

Stockholders' Equity

7. Stockholders’ Equity

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, if and when, declared by the Company’s Board of Directors.

Preferred Stock

The Company is authorized to issue 5.0 million shares of undesignated preferred stock in one or more series. As of March 31, 2020, 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:

	March 31, 2020		December 31, 2019
	(unaudited)
Common stock options outstanding		6,766,589		5,744,036
Options available for grant under Equity Incentive Plans		1,187,072		938,738
		7,953,661		6,682,774

Stock-based Compensation

3 Months Ended

Mar. 31, 2020

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. Effective January 1, 2020, and in accordance with the “evergreen” provision of the 2017 plan, an additional 1,096,553 shares were made available for issuance.

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 March 31, 2020, there were a total of 1,187,072 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 months ended March 31, 2020, the Company recorded employee share-based compensation expense of $4.7 million. During the three months ended March 31, 2019, the Company recorded employee share-based compensation expense of $3.7 million.

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. During the three months ended March 31, 2020, the Company did not have any non-employee share-based compensation expense. During the three months ended March 31, 2019, the Company recorded non-employee share-based compensation expense of $0.1 million.

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 months ended March 31, 2020 and March 31, 2019:

	Three Months Ended March 31,
	2020	2019
	(unaudited)
Expected volatility	74.8 - 78.3%	77.8 - 82.1%
Weighted-average risk free rate	0.4 - 1.7%	2.5 - 2.6%
Dividend yield	—%	—%
Expected term (in years)	6.06	6.08

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

	Three Months Ended March 31,
	2020		2019
	(unaudited)
Research and development	$	1,800	$	1,494
General and administrative		2,927		2,310
Total stock-based compensation expense	$	4,727	$	3,804

Stock Option Activity

Stock option activity for the three months ended March 31, 2020 is as follows:

						Weighted average
				Weighted
				average		Remaining		Aggregate
	Options			exercise		contractual		intrinsic
	outstanding			price		life (Years)		value
								(in thousands)
Balance as of December 31, 2019		5,744,036		$	16.88		7.5	$	72,251
Cancelled		(247,818	)	$	33.67
Granted		1,396,037			18.67
Exercised		(125,666	)		1.74
Balance as of March 31, 2020		6,766,589		$	16.92		7.8	$	19,809
Exercisable at December 31, 2019		3,001,179			8.93		6.1	$	58,797
Vested at December 31, 2019 and expected to vest		5,744,036			16.88		7.5	$	72,251
Exercisable at March 31, 2020		3,260,268			10.60		6.2	$	19,545
Vested at March 31, 2020 and expected to vest		6,766,589			16.92		7.8	$	19,809

Net Loss Per Common Share

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

Net Loss Per Common Share

9. 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 March 31, 2020 and 2019, 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 March 31,
	2020		2019
	(unaudited)
Stock options issued and outstanding		6,276,155		5,156,076
		6,276,155		5,156,076

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

Related Party Transactions

3 Months Ended

Mar. 31, 2020

Related Party Transactions

10. Related party transactions

The Company maintains a consulting agreement with a member of the Board of Directors for scientific advisory services outside of his role on the Board of Directors that expires on June 30, 2020.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed 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 financial position and results of operations for the interim periods presented. The information presented in the condensed financial statements and related notes as of March 31, 2020, and for the three months ended March 31, 2020 and 2019, is unaudited. The results for the three months ended March 31, 2020 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 Annual Report on Form 10-K for the year ended December 31, 2019 filed with the SEC on February 26, 2020 (collectively, “2019 Form 10-K”). The December 31, 2019 condensed 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 U.S. 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.
Research and Development	Research and Development Research and development expenses consist of costs incurred to further the Company’s research and development activities and include salaries and related employee benefits, manufacturing of pharmaceutical active ingredients and drug products, costs associated with clinical trials, nonclinical activities, regulatory activities, research-related overhead expenses and fees paid to expert consultants, external service providers and contract research organizations which conduct certain research and development activities on behalf of the Company. Costs incurred in the research and development of products are charged to research and development expense as incurred. Each reporting period, management estimated and accrued research and development expenses, including external clinical study costs associated with clinical trial activities. The process of estimating and accruing expenses involves reviewing contracts and purchase orders, identifying services that have been provided on the Company’s behalf, and estimating the level of service performed and the associated cost incurred for the service when the Company has not yet been invoiced or otherwise notified of the actual costs. Costs for clinical trial activities were estimated based on an evaluation of vendors’ progress towards completion of specific tasks, using data such as patient enrollment, clinical site activations or information provided by vendors regarding their actual costs incurred. Payments for these activities are based on the terms of individual contracts and payment timing may differ significantly from the period in which the services were performed. The Company determines accrual estimates through reports from and discussions with applicable personnel and outside service providers as to the progress or state of completion of trials, or the services completed. The estimates of accrued external clinical study costs as of each balance sheet date are based on the facts and circumstances known at the time.
Income Taxes	Income taxes The Company did not record a federal or state income tax benefit for the three months ended March 31, 2020 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 March 31, 2020 and December 31, 2019, 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 March 31, 2020 and December 31, 2019, 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.
Coronoavirus (COVID-19) Impact on Operations	Coronavirus (COVID-19) impact on operations The Company has implemented business continuity plans to address the COVID-19 pandemic and minimize disruptions to ongoing operations. The timeline for filing the trilaciclib NDA has not been impacted by COVID-19, and the Company expects to complete the NDA filing in the second quarter of 2020. Initiation of two clinical trials, the rintodestrant/palbociclib combination trial and the I-SPY 2 trial, is on track to begin in the second quarter of 2020. Initial enrollment of these trials is likely to be impacted by COVID-19. The Company does not anticipate significant supply chain delays or shortages as a result of the COVID-19 pandemic.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Adopted Accounting Standards In August 2018, the FASB issued ASU No. 2018-15, Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”). The FASB issued ASU 2018-15 to align the requirements for capitalizing implementation costs incurred in a cloud-based hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). ASU 2018-15 became effective for annual and interim reporting periods beginning after December 15, 2019. The Company adopted ASU 2018-15 on January 1, 2020 using the prospective method of adoption, and the adoption did not have a material impact to the financial statements.

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32847-109319

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
-SubTopic 740
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6491622&loc=d3e9504-115650

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 17
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32809-109319

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=116657188&loc=SL116659661-227067

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Summary of Financial Instruments and Respective Fair Values

At March 31, 2020 and December 31, 2019 these financial 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 March 31, 2020

Assets
Money market funds	$	225,886	$	—	$	—	$	225,886
Certificates of Deposit		15,942		—		—		15,942
Total assets at fair value:	$	241,828	$	—	$	—	$	241,828

	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, 2019
Assets
Money market funds	$	252,563	$	—	$	—	$	252,563
Certificates of Deposit		15,873		—		—		15,873
Total assets at fair value:	$	268,436	$	—	$	—	$	268,436

Property and Equipment (Tables)

3 Months Ended

Mar. 31, 2020

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

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

	March 31, 2020			December 31, 2019

Computer equipment	$	330		$	332
Laboratory equipment		865			871
Furniture and fixtures		1,071			1,071
Leasehold improvements		1,941			1,941
Accumulated depreciation		(836	)		(677	)
Property and equipment, net	$	3,371		$	3,538

Accrued Expenses (Tables)

3 Months Ended

Mar. 31, 2020

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses are comprised as follows (in thousands):

	March 31, 2020		December 31, 2019

Accrued external research	$	2,216	$	2,737
Accrued professional fees and other		1,914		1,487
Accrued external clinical study costs		7,596		7,996
Accrued compensation expense		956		3,183
Accrued expenses	$	12,682	$	15,403

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2020

Equity [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:

	March 31, 2020		December 31, 2019
	(unaudited)
Common stock options outstanding		6,766,589		5,744,036
Options available for grant under Equity Incentive Plans		1,187,072		938,738
		7,953,661		6,682,774

- 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://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 11: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 12: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 210
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-Section S99
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-Subparagraph (SX 210.5-02(27))
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Reference 13: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 14: http://fasb.org/us-gaap/role/ref/legacyRef
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+ Details

Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Summary of Stock Option Activity

Stock option activity for the three months ended March 31, 2020 is as follows:

						Weighted average
				Weighted
				average		Remaining		Aggregate
	Options			exercise		contractual		intrinsic
	outstanding			price		life (Years)		value
								(in thousands)
Balance as of December 31, 2019		5,744,036		$	16.88		7.5	$	72,251
Cancelled		(247,818	)	$	33.67
Granted		1,396,037			18.67
Exercised		(125,666	)		1.74
Balance as of March 31, 2020		6,766,589		$	16.92		7.8	$	19,809
Exercisable at December 31, 2019		3,001,179			8.93		6.1	$	58,797
Vested at December 31, 2019 and expected to vest		5,744,036			16.88		7.5	$	72,251
Exercisable at March 31, 2020		3,260,268			10.60		6.2	$	19,545
Vested at March 31, 2020 and expected to vest		6,766,589			16.92		7.8	$	19,809

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 months ended March 31, 2020 and March 31, 2019:

	Three Months Ended March 31,
	2020	2019
	(unaudited)
Expected volatility	74.8 - 78.3%	77.8 - 82.1%
Weighted-average risk free rate	0.4 - 1.7%	2.5 - 2.6%
Dividend yield	—%	—%
Expected term (in years)	6.06	6.08

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 March 31,
	2020		2019
	(unaudited)
Research and development	$	1,800	$	1,494
General and administrative		2,927		2,310
Total stock-based compensation expense	$	4,727	$	3,804

Net Loss Per Common Share (Tables)

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

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

For the three months ended March 31, 2020 and 2019, 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 March 31,
	2020		2019
	(unaudited)
Stock options issued and outstanding		6,276,155		5,156,076
		6,276,155		5,156,076

Business Description - Additional Information (Details)	3 Months Ended
Business Description - Additional Information (Details)	Mar. 31, 2020 Product
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of clinical-stage product candidates from pipeline	3

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended
	Mar. 31, 2020 USD ($) Trial	Dec. 31, 2019 USD ($)
Accounting Policies [Abstract]
Federal, state income tax benefit	$ 0
Unrecognized income tax benefits	0	$ 0
Accrued income taxes	$ 0	$ 0
Number of clinical trials initiated related to COVID-19 \| Trial	2

Fair Value Measurements - Summary of Financial Instruments and Respective Fair Values (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets
Assets at fair value	$ 241,828	$ 268,436
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Assets at fair value	241,828	268,436
Money Market Funds
Assets
Assets at fair value	225,886	252,563
Money Market Funds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Assets at fair value	225,886	252,563
Certificates of Deposit
Assets
Assets at fair value	15,942	15,873
Certificates of Deposit \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Assets at fair value	$ 15,942	$ 15,873

Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Changes in valuation methodology	$ 0	$ 0

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Accumulated depreciation	$ (836)	$ (677)
Property and equipment, net	3,371	3,538
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	330	332
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	865	871
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,071	1,071
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,941	$ 1,941

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation expenses relating to property and equipment	$ 159	$ 64

Patent License Agreement - Additional Information (Details) - USD ($)	3 Months Ended			40 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2016	Mar. 31, 2020
Patent License Agreement [Line Items]
Non-refundable license issue fee	$ 20,434,000	$ 18,080,000
University
Patent License Agreement [Line Items]
License agreement date	Nov. 23, 2016
License agreement amendment date	Mar. 24, 2017
Milestone payments	$ 0			$ 600,000
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 determined 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 within 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
University \| Maximum
Patent License Agreement [Line Items]
Milestone payments	$ 2,600,000
University \| License
Patent License Agreement [Line Items]
Non-refundable license issue fee			$ 500,000

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued external research	$ 2,216	$ 2,737
Accrued professional fees and other	1,914	1,487
Accrued external clinical study costs	7,596	7,996
Accrued compensation expense	956	3,183
Accrued expenses	$ 12,682	$ 15,403

Stockholders' Equity - Additional Information (Details) - shares	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Equity [Abstract]
Common stock, shares authorized	120,000,000	120,000,000
Common stock, voting rights	Holders of common stock are entitled to one vote per share.
Undesignated preferred stock, shares authorized to issue	5,000,000.0
Preferred stock, shares issued	0
Preferred stock, shares outstanding	0

Stockholders' Equity - Summary of Common Stock Shares Reserved for Future Issuance (Details) - shares	Mar. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance	7,953,661	6,682,774
Common Stock Options Outstanding
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance	6,766,589	5,744,036
Options Available For Grant Under Equity Incentive Plan
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance	1,187,072	938,738

Stock-based Compensation - Additional Information (Details) - USD ($)		3 Months Ended
	Jan. 01, 2020	Mar. 31, 2020	Mar. 31, 2019	May 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense		$ 4,727,000	$ 3,804,000
Employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options, maximum term		10 years
Share-based compensation expense		$ 4,700,000	3,700,000
Non-employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense		$ 0	$ 100,000
2011 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant under equity incentive plan		0
2017 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant under equity incentive plan		1,187,072
Number of shares approved for grant under equity incentive plan				1,932,000
Number of additional shares approved for grant under equity incentive plan	1,096,553

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
	Mar. 31, 2020	Mar. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	74.80%	77.80%
Expected volatility, maximum	78.30%	82.10%
Weighted-average risk free rate, minimum	0.40%	2.50%
Weighted-average risk free rate, maximum	1.70%	2.60%
Expected term (in years)	6 years 21 days	6 years 29 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
	Mar. 31, 2020	Mar. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 4,727	$ 3,804
Research and development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	1,800	1,494
General and administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 2,927	$ 2,310

Stock-based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Options outstanding
Beginning balance	5,744,036
Cancelled	(247,818)
Granted	1,396,037
Exercised	(125,666)
Ending balance	6,766,589	5,744,036
Exercisable	3,260,268	3,001,179
Vested and expected to vest	6,766,589	5,744,036
Weighted average exercise price
Beginning balance	$ 16.88
Cancelled	33.67
Granted	18.67
Exercised	1.74
Ending balance	16.92	$ 16.88
Exercisable	10.60	8.93
Vested and expected to vest	$ 16.92	$ 16.88
Weighted average, Remaining contractual for life (Years)
Balance	7 years 9 months 18 days	7 years 6 months
Exercisable	6 years 2 months 12 days	6 years 1 month 6 days
Vested and expected to vest	7 years 9 months 18 days	7 years 6 months
Weighted average, Aggregate intrinsic value
Balance	$ 19,809	$ 72,251
Exercisable	19,545	58,797
Vested and expected to vest	$ 19,809	$ 72,251

Net Loss Per Common Share - Schedule of Potentially Dilutive Securities Excluded from Computations of Diluted Weighted-average Shares Outstanding (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computations of diluted weighted-average shares outstanding	6,276,155	5,156,076
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	6,276,155	5,156,076

Related Party Transactions - Additional Information (Details)	3 Months Ended
	Mar. 31, 2020
Scientific Advisory \| Chairman of the Board of Directors
Related Party Transaction [Line Items]
Consulting agreements expiration date	Jun. 30, 2020