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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2020	Jul. 31, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
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		38,014,603
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	Jun. 30, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 234,267	$ 269,208
Restricted cash	63	63
Prepaid expenses and other current assets	5,761	1,732
Total current assets	240,091	271,003
Property and equipment, net	3,213	3,538
Restricted cash	437	437
Operating lease assets	8,495	9,853
Other assets	1,361
Total assets	253,597	284,831
Current liabilities
Accounts payable	2,816	3,684
Accrued expenses	18,306	15,403
Other current liabilities	802	682
Total current liabilities	21,924	19,769
Loan payable	19,453
Operating lease liabilities	8,375	9,535
Total liabilities	49,752	29,304
Stockholders’ equity
Common stock, $0.0001 par value, 120,000,000 shares authorized as of June 30, 2020 and December 31, 2019, respectively; 37,939,066 and 37,638,260 shares issued as of June 30, 2020 and December 31, 2019, respectively; 37,912,400 and 37,611,594 shares outstanding as of June 30, 2020 and December 31, 2019, respectively	4	4
Treasury stock, 26,666 shares	(8)	(8)
Additional paid-in capital	602,935	592,384
Accumulated deficit	(399,086)	(336,853)
Total stockholders’ equity	203,845	255,527
Total liabilities and stockholders' equity	$ 253,597	$ 284,831

Condensed Balance Sheets (Parenthetical) (unaudited) - $ / shares	Jun. 30, 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	37,939,066	37,638,260
Common stock, shares, outstanding	37,912,400	37,611,594
Treasury stock, shares	26,666	26,666

Condensed Statements of Operations (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
License revenue - related party	$ 2,140		$ 2,140
Revenue, Product and Service [Extensible List]	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 18,531	$ 23,489	$ 38,965	$ 41,569
General and administrative	14,431	9,094	25,818	16,896
Total operating expenses	32,962	32,583	64,783	58,465
Loss from operations	(30,822)	(32,583)	(62,643)	(58,465)
Other income (expense):
Interest income	91	1,893	872	3,809
Interest expense	(265)		(265)
Other income (expense)	(214)		(197)	14
Total other income (expense), net	(388)	1,893	410	3,823
Net loss	$ (31,210)	$ (30,690)	$ (62,233)	$ (54,642)
Net loss per share, basic and diluted	$ (0.83)	$ (0.82)	$ (1.65)	$ (1.46)
Weighted average common shares outstanding, basic and diluted	37,786,208	37,470,926	37,722,965	37,434,156

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, 2018	358,820	$ 4	$ (8)	573,230	(214,406)
Balance (in shares) at Dec. 31, 2018		37,268,792	(26,666)
Net loss during quarter	(54,642)
Balance at Jun. 30, 2019	312,670	$ 4	$ (8)	581,722	(269,048)
Balance (in shares) at Jun. 30, 2019		37,530,607	(26,666)
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)
Exercise of common stock options	678			678
Exercise of common stock options (in shares)		42,925
Stock-based compensation	3,741			3,741
Net loss during quarter	(30,690)				(30,690)
Balance at Jun. 30, 2019	312,670	$ 4	$ (8)	581,722	(269,048)
Balance (in shares) at Jun. 30, 2019		37,530,607	(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
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)
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 (in shares)	300,806
Net loss during quarter	$ (62,233)
Balance at Jun. 30, 2020	203,845	$ 4	$ (8)	602,935	(399,086)
Balance (in shares) at Jun. 30, 2020		37,939,066	(26,666)
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)
Exercise of common stock options	1,238			1,238
Exercise of common stock options (in shares)		175,140
Stock-based compensation	4,367			4,367
Net loss during quarter	(31,210)				(31,210)
Balance at Jun. 30, 2020	$ 203,845	$ 4	$ (8)	$ 602,935	$ (399,086)
Balance (in shares) at Jun. 30, 2020		37,939,066	(26,666)

- Definition

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

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+ Details

- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

+ References + Details

Condensed Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net loss	$ (62,233)	$ (54,642)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation	9,094	7,545
Depreciation and amortization	317	129
Loss on disposal of fixed assets	8
Amortization of debt issuance costs	88
Non-cash interest expense	177
Non-cash equity interest, net	(926)
Change in operating assets and liabilities
Prepaid expenses and other assets	(622)	(1,828)
Accounts payable	(868)	(713)
Accrued expenses and other liabilities	(908)	5,075
Net cash used in operating activities	(55,873)	(44,434)
Cash flows from investing activities
Purchases of property and equipment		(392)
Net cash used in investing activities		(392)
Cash flows from financing activities
Proceeds from stock options exercised	1,457	947
Proceeds from loan agreement	20,000
Payments of debt issuance costs	(525)
Net cash provided by financing activities	20,932	947
Net change in cash, cash equivalents and restricted cash	(34,941)	(43,879)
Cash, cash equivalents and restricted cash
Beginning of period	269,708	369,290
End of period	234,767	325,411
Non-cash operating, investing and financing activities
Upfront project costs and other current assets in accounts payable and accrued expenses	2,500	522
Purchases of equipment in accounts payable		$ 106
Debt issuance costs included in accrued expenses	$ 95

Business Description

6 Months Ended

Jun. 30, 2020

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 focused on the discovery, development and commercialization of novel small molecule therapeutics for the treatment of patients with cancer. The Company was incorporated on May 19, 2008 in the state of Delaware.

The Company is advancing three clinical-stage programs. Trilaciclib is a first-in-class therapy designed to improve outcomes for patients who are treated with chemotherapy. Rintodestrant is a potential best-in-class oral selective estrogen receptor degrader (SERD) for the treatment of estrogen receptor-positive (ER+) breast cancer. Lerociclib is a differentiated oral CDK4/6 inhibitor designed to enable more effective combination treatment strategies across multiple oncology indications, including ER+, HER2-negative (HER2-) breast cancer. The Company also has intellectual property focused on cyclin-dependent kinase targets.

Trilaciclib, the Company’s most advanced clinical-stage candidate, is a first-in-class therapy designed to preserve bone marrow and immune system function during chemotherapy and improve patient outcomes. The U.S. Food and Drug Administration (FDA) has granted Breakthrough Therapy Designation for trilaciclib based on myelopreservation data from three randomized, double-blind, placebo-controlled small cell lung cancer (SCLC) clinical trials, as well as safety data collected across all completed and ongoing clinical trials. The Breakthrough Therapy program is designed to expedite development and review of drugs intended for serious or life-threatening conditions. In June 2020, the Company submitted a New Drug Application (NDA) for trilaciclib in small cell lung cancer to the FDA. The Company entered into a three-year co-promotion agreement for trilaciclib in the United States and Puerto Rico with Boehringer Ingelheim in June 2020. Under the terms of the agreement, G1 will book revenue in the United States and Puerto Rico and retain development and commercialization rights to trilaciclib. G1 will lead marketing, market access and medical engagement initiatives; Boehringer Ingelheim will lead sales force engagements. The agreement is limited to support for small cell lung cancer. In addition, discussions with European regulatory authorities have indicated existing data is sufficient to support a Marketing Authorization Application (MAA) to the European Medicines Agency (EMA) for trilaciclib for myelopreservation in SCLC, which the Company plans to pursue in collaboration with a partner. In September 2019, the Company presented updated data from a randomized Phase 2 trial of trilaciclib in combination with chemotherapy in metastatic triple-negative breast cancer (mTNBC). The results of the trial demonstrated significant improvement in overall survival, or (OS) (preliminary). Though the trial did not meet the primary myelopreservation endpoints, patients receiving trilaciclib were able to receive approximately 50% more cycles of chemotherapy, without additional hematological toxicity. These data were presented at the 2019 European Society for Medical Oncology (ESMO) Congress and were concurrently published in The Lancet Oncology. In January 2020, the Company announced that trilaciclib is being included in a new randomized, investigational treatment arm for the ongoing I-SPY 2 TRIAL™ for neoadjuvant treatment of locally advanced breast cancer. The trial, which was initiated in the second quarter of 2020, and run by the non-profit Quantum Leap Healthcare Collaborative, is designed to rapidly screen promising experimental treatments and identify those most effective in specific patient subgroups based on molecular characteristics (biomarker signatures). The Company is planning to initiate a randomized, placebo-controlled Phase 3 trial of trilaciclib in colorectal cancer in the fourth quarter of 2020. In August 2020, the Company entered into an exclusive license agreement with Nanjing Simcere Dongyuan Pharmaceutical Co., Ltd (“Simcere”) for development and commercialization rights for trilaciclib in all indications in Greater China (mainland China, Hong Kong, Macau and Taiwan). Under the terms of the agreement, the Company will receive an upfront payment of $14.0 million and be eligible to receive up to $156.0 million in development and commercial milestone payments. Simcere will also pay the Company tiered low double-digit royalties on annual net sales of trilaciclib in Greater China. As part of this agreement, Simcere will participate in global clinical trials of trilaciclib and the companies will be responsible for all development and commercialization costs in their respective territories.

The Company is developing rintodestrant, a potential best-in-class oral SERD, as a monotherapy and in combination with the CDK4/6 inhibitors, initially Ibrance® (palbociclib), for the treatment of ER+ breast cancer. In 2018, the Company initiated a Phase 1/2a (dose escalation/dose expansion) clinical trial in ER+, HER2- breast cancer. Preliminary data from the Phase 1 potion of this trial were presented at the 2019 ESMO Congress, showing that rintodestrant was well tolerated and demonstrated evidence of anti-tumor activity in heavily pre-treated patients. The Company has completed enrollment of the dose escalation and dose expansion portions of the trial, and based on these findings the Company plans to advance an 800 mg dose of rintodestrant in future trials. The Company plans to present additional safety and efficacy data from this trial in the fourth quarter of 2020. The Company initiated enrollment of patients receiving rintodestrant in combination with palbociclib in the second quarter of 2020. Palbociclib is being provided under a non-exclusive clinical supply agreement that was signed with Pfizer in February 2020.

Lerociclib is a differentiated oral CDK4/6 inhibitor being developed for use in combination with other targeted therapies in multiple oncology indications, including ER+, HER2- breast cancer. The Company reported encouraging updated results from its Phase 1/2 trial in ER+, HER2- breast cancer (in combination with fulvestrant) at the 2019 San Antonio Breast Cancer Symposium. The Company also initiated a Phase 1b combination trial with the epidermal growth factor receptor (EGFR) inhibitor, Tagrisso® (osimertinib) in non-small cell lung cancer. Initial safety and tolerability data from this trial were presented at the 2019 ESMO Congress. In 2020, the Company entered into separate, exclusive agreements with EQRx, Inc. (rights for U.S., Europe, Japan and all markets outside Asia-Pacific) and Genor Biopharma Co. Inc. (rights for Asia-Pacific, excluding Japan) for the development and commercialization of lerociclib in all indications. Combined, these agreements provide $26.0 million in upfront payments to the Company, and up to $330.0 million in potential milestone payments, plus sales-based royalties. EQRx, Inc. and Genor Biopharma Co. Inc. are responsible for all costs related to the development and commercialization of lerociclib in their respective territories.

The Company also entered into an exclusive license agreement with ARC Therapeutics, LLC (“ARC”), a company primarily owned by a related party, in May 2020. The Company granted ARC an exclusive, worldwide, royalty-bearing license of its CDK2 inhibitor compounds in exchange for an upfront payment and equity in ARC with a total value of approximately $2.1 million, which resulted in the recognition of related party revenue as discussed in Note 10. The Company is entitled to receive an additional milestone payment and sales-based royalties, and has right of first negotiation to re-acquire these assets.

Basis of Presentation and Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2020

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

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 June 30, 2020, and for the three and six months ended June 30, 2020 and 2019, is unaudited. The results for the six months ended June 30, 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. Certain amounts have been reclassified to conform to current presentation.

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.

Revenue Recognition

For elements of those arrangements that we determine should be accounted for under ASC 606, Revenue from Contracts with Customers (“ASC 606”), we assess which activities in our license or collaboration agreements are performance obligations that should be accounted for separately and determine the transaction price of the arrangement, which includes the assessment of the probability of achievement of future milestones and other potential consideration. For arrangements that include multiple performance obligations, such as granting a license or performing manufacturing or research and development activities, we allocate the transaction price based on the relative standalone selling price and recognize revenue that is allocated to the respective performance obligation when (or as) control is transferred to the customer and the performance obligation is satisfied. Accordingly, we develop assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. These key assumptions may include revenue forecasts, clinical development timelines and costs, discount rates and probabilities of clinical and regulatory success.

Licenses of intellectual property

If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue associated with the bundled performance obligation. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of progress and related revenue recognition.

Milestone Payments

At the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. The Company evaluates each milestone to determine when and how much of the milestone to include in the transaction price. The Company first estimates the amount of the milestone payment that the Company could receive using either the expected value or the most likely amount approach. The Company primarily uses the most likely amount approach as that approach is generally most predictive for milestone payments with a binary outcome. Then, the Company considers whether any portion of that estimated amount is subject to the variable consideration constraint (that is, whether it is probable that a significant reversal of cumulative revenue would not occur upon resolution of the uncertainty). The Company updates the estimate of variable consideration included in the transaction price at each reporting date which includes updating the assessment of the likely amount of consideration and the application of the constraint to reflect current facts and circumstances.

Royalties

For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any revenue related to sales-based royalties or milestone payments based on the level of sales.

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

The Company did not record a federal or state income tax benefit for the six months ended June 30, 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 June 30, 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 June 30, 2020 and December 31, 2019, 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.

Debt Issuance Costs

Debt issuance costs are amortized to interest expense over the estimated life of the related debt based on the effective interest method. In accordance with ASC 835, Interest, we present debt issuance costs on the condensed balance sheet as a direct deduction from the associated debt.

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. Initiation of two clinical trials, the rintodestrant/palbociclib combination trial and the I-SPY 2 trial, began in the second quarter of 2020 as scheduled. 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

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.

Fair Value Measurements

6 Months Ended

Jun. 30, 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 June 30, 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 June 30, 2020
Assets
Money market funds	$	216,815	$	—	$	—	$	216,815
Certificates of Deposit		15,957		—		—		15,957
Total assets at fair value:	$	232,772	$	—	$	—	$	232,772

	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 and six months ended June 30, 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

6 Months Ended

Jun. 30, 2020

Property Plant And Equipment [Abstract]

Property and Equipment

4. Property and Equipment

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

	June 30, 2020			December 31, 2019

Computer equipment		330			332
Laboratory equipment		862			871
Furniture and fixtures		1,071			1,071
Leasehold improvements		1,941			1,941
Accumulated depreciation		(991	)		(677	)
Property and equipment, net	$	3,213		$	3,538

Depreciation expense relating to property and equipment was $158 thousand and $317 thousand for the three and six months ended June 30, 2020, respectively, and $65 thousand and $129 thousand for the three and six months ended June 30, 2019, respectively.

Patent License Agreement

6 Months Ended

Jun. 30, 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 a 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 million was incurred during the current quarter. 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

6 Months Ended

Jun. 30, 2020

Payables And Accruals [Abstract]

Accrued Expenses

6. Accrued Expenses

Accrued expenses are comprised as follows (in thousands):

	June 30, 2020		December 31, 2019

Accrued external research	$	2,206	$	2,737
Accrued professional fees and other		7,527		1,487
Accrued external clinical study costs		6,764		7,996
Accrued compensation expense		1,809		3,183
Accrued expenses	$	18,306	$	15,403

Loan Payable

6 Months Ended

Jun. 30, 2020

Debt Disclosure [Abstract]

Loan Payable

7. Loan Payable

On May 29, 2020, the Company entered into a loan and security agreement (the “Loan Agreement”) with Hercules Capital, Inc. (“Hercules”), under which Hercules has agreed to lend the Company up to $100.0 million, to be made available in a series of tranches, subject to certain terms and conditions. The first tranche totals $30.0 million, of which the Company received $20.0 million at closing. Upon satisfaction of certain milestones, the second tranche of $20.0 million will become available to the Company for drawdown through December 15, 2021. The third tranche of $30.0 million will be available based on the Company’s maintenance of specified covenants through December 31, 2022. The fourth tranche of $20.0 million will be available at Hercules’ approval through December 31, 2022.

Amounts borrowed under the Loan Agreement will bear an interest rate equal to the greater of either (i) (a) the prime rate as reported in The Wall Street Journal, plus (b) 6.40%, and (ii) 9.65%. The Company will make interest only payments through June 1, 2022. The interest only period may be extended through January 1, 2023 upon satisfaction of certain milestones. Following the interest only period, the Company will repay the principal balance and interest of the advances in equal monthly installments through June 1, 2024.

The Company may prepay advances under the Loan Agreement, in whole or in part, at any time subject to a prepayment charge equal to (a) 3.0% of the prepayment amount in the first year; (b) 2.0% of the prepayment amount in the second year; and (b) 1.0% of the prepayment amount in the third year.

Upon prepayment or repayment of all or any of the advances under the Loan Agreement, the Company will pay (in addition to the prepayment charge) an end of term charge of 6.95% of the aggregate funded amount. With respect to the first tranche, the end of term charge of $2.1 million will be payable upon any prepayment or repayment. To the extent that the Company is provided additional advances under the Loan Agreement, the 6.95% end of term charge will be applied to such additional amounts. These amounts will be accrued over the term of the loan using effective-interest method.

The Loan Agreement is secured by substantially all of the Company’s assets, including intellectual property, subject to certain exemptions. The Company is permitted to out-license lerociclib in arms-length transactions and the Company is permitted to out-license rintodestrant upon approval of the licensing terms by Hercules.

The Company incurred financing expenses of $0.4 million related to the Loan Agreement which are recorded as debt issuance costs and as a direct reduction to long-term debt on the Company’s unaudited condensed balance sheet. Additionally, the Company is treating a portion of the upfront facility fee that related to the initial $20.0 million drawn as a debt discount and treating it in the same way as debt issuance costs. The remainder of the facility fee is related to future undrawn tranches and is accounted for as a deferred financing charge.

Upon issuance, the first tranche was recorded as a liability with an initial carrying value of $19.4 million, net of debt discount and debt issuance costs. The initial carrying value will be accreted to the repayment amount, which includes the outstanding principal plus the end of term charge, through interest expense using the effective-interest method over the term of the debt. During the six months ended June 30, 2020, the Company recognized $0.3 million of interest expense related to the Loan Agreement, which is reflected in other income (expense), net on the unaudited condensed statements of operations.

As of June 30, 2020 the future principal payments due under the Loan Agreement, excluding interest, are as follows:

	Amount

Remainder of 2020	$	—
2021		—
2022		4,631
2023		9,972
2024		5,397
Total principal outstanding		20,000
End of term charge		56
Unamortized debt issuance costs		(603	)
Total		19,453

Stockholders' Equity

6 Months Ended

Jun. 30, 2020

Equity [Abstract]

Stockholders' Equity

8. 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, as, 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 June 30, 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:

	June 30, 2020		December 31, 2019

Common stock options outstanding		6,539,518		5,744,036
Options available for grant under Equity Incentive Plans		1,239,003		938,738
		7,778,521		6,682,774

Stock-Based Compensation

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

9. 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 June 30, 2020, there were a total of 1,239,003 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.

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 six months ended June 30, 2020 and June 30, 2019:

	Three Months Ended June 30,		Six Months Ended June 30,
	2020	2019	2020		2019

Expected volatility	78.5 - 79.7%	74.2 - 77.0%	74.8 - 79.7%		74.2 - 82.1%
Weighted-average risk free rate	0.4%	1.9 - 2.4%	0.4 - 1.7%		1.9 - 2.6%
Dividend yield	—%	—%	—%		—%
Expected term (in years)	5.68	5.82		6.01	6.0

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019

Research and development	$	1,834	$	1,507	$	3,634	$	3,002
General and administrative		2,533		2,234		5,460		4,543
Total stock-based compensation expense	$	4,367	$	3,741	$	9,094	$	7,545

Stock Option Activity

Stock option activity for the six months ended June 30, 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		(506,749	)	$	32.74
Granted		1,603,037			18.35
Exercised		(300,806	)		4.84
Balance as of June 30, 2020		6,539,518		$	16.57		7.6	$	65,133
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 June 30, 2020		3,290,661			10.61		6.1	$	51,632
Vested at June 30, 2020 and expected to vest		6,539,518			16.57		7.6	$	65,133

License Revenue

6 Months Ended

Jun. 30, 2020

Revenue Recognition [Abstract]

License Revenue

10. License Revenue

ARC License Agreement

On May 22, 2020, the Company entered into an exclusive license agreement with ARC Therapeutics, LLC (“ARC”), a company primarily owned by a related party, whereby G1 granted to ARC an exclusive, worldwide, royalty-bearing license, with the right to sublicense, solely to make, have made, use, sell, offer for sale, import, export, and commercialize products related to its cyclin dependent kinase 2 (“CDK2”) inhibitor compounds. At close, G1 received consideration in the form of an upfront payment of $1.0 million and an equity interest in ARC equal to 10% of its issued and outstanding units. In addition, the Company may receive a future development milestone payment totaling $2.0 million and royalty payments in the mid-single digits based on net sales of the licensed compound after commercialization. The Company has right of first negotiation to re-acquire these assets.

The Company assessed the license agreement in accordance with ASC 606 and identified one performance obligation in the contract, which is the transfer of the license, as ARC can benefit from the license using its own resources. The Company recognized $2.1 million in license revenue consisting of the upfront payment and the 10% equity interest in ARC upon the effective date as the Company determined the license was a right to use the intellectual property and the Company had provided all necessary information to ARC to benefit from the license.

The Company considers the future potential development milestones and sales-based royalties to be variable consideration. The development milestone is excluded from the transaction price because it determined the payment to be fully constrained under ASC 606 due to the inherent uncertainty in the achievement of such milestone due to factors outside of the Company’s control. As sales-based royalties are all related to the license of the intellectual property, the Company will recognize revenue in the period when subsequent sales are made pursuant to the sales-based royalty exception. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. As of June 30, 2020, the Company had received the upfront cash payment and the equity interest, and there are no contract assets or liabilities related to this agreement.

Genor License Agreement

On June 15, 2020, the Company entered into an exclusive license agreement with Genor Biopharma Co. Inc. (“Genor”) for the development and commercialization of lerociclib in the Asia-Pacific region, excluding Japan (the “Licensed Territory”). Under the license agreement, the Company granted to Genor an exclusive, royalty-bearing, non-transferable license, with the right to grant sublicenses, to develop, obtain, hold and maintain regulatory approvals for, and commercialize lerociclib, in the Licensed Territory.

Under the license agreement, Genor agreed to pay the Company a non-refundable, upfront cash payment of $6.0 million with the potential to pay an additional $40.0 million upon reaching certain development and commercial milestones. In addition, Genor will pay the Company tiered royalties ranging from high single to low double-digits based on annual net sales of lerociclib in the Licensed Territory. The upfront cash payment is payable within 30 days of the effective date of the license agreement. In return, the Company will furnish to Genor the related know-how that is necessary to develop, seek regulatory approval for, or commercialize lerociclib in the Licensed Territory. Genor will be responsible for the development of product in the Licensed Territory and will be responsible, at its sole cost, for obtaining supply of lerociclib to meet its development, regulatory approval for, and commercialization obligations under the agreement.

The Company assessed the license agreement in accordance with ASC 606 and identified the following promises under the contract: (i) to transfer the license, (ii) technology transfer and the transfer of related know-how to occur within 60 days of the effective date of the license agreement, and (iii) the sale and delivery of certain existing inventory specified in the agreement. The Company assessed the promised goods and services to determine if they are distinct. Based on this assessment, the Company determined that Genor cannot benefit from the license separate from the technology transfer and related know-how as they are highly interrelated and therefore not distinct. Accordingly, the transfer of the license and the related know-how represent one combined performance obligation.

In accordance with ASC 606, the Company determined the transaction price at contract inception. The Company considers the future potential development and sales milestones, as well as the sales-based royalties to be variable consideration. The Company excluded the regulatory-based development and sales milestones from the transaction price because it determined such payments to be fully constrained under ASC 606 due to the inherent uncertainty in the achievement of such milestone payments and are highly susceptible to factors outside our control. As the sales-based royalties are all related to the license of the intellectual property, the Company will recognize revenue in the period when subsequent sales are made pursuant to the sales-based royalty exception. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. Based on the foregoing, the Company determined that the $6.0 million non-refundable, upfront payment and the $0.6 million owed upon the delivery of existing inventory constituted the entirety of consideration to be included in the transaction price.

The Company then allocated the transaction price to the performance obligations based on the relative stand-alone selling price of each distinct obligation. The Company determined the stand-alone selling prices to equal the amounts paid for each performance obligation. Revenue is recognized for each performance obligation based at a point in time in which control has been transferred. The performance obligation for the transfer of the license and related technology and know-how does not occur until the delivery of the related know-how has been satisfied. As of June 30, 2020, this performance obligation has not been satisfied and therefore revenue has not been recognized. The transfer of the license’s related technology and know-how is expected to occur in the third quarter of 2020. In addition, the delivery of the existing inventory is expected to occur in the third quarter of 2020, at which point revenue will be recognized. As of June 30, 2020, the Company had not received the upfront cash payment.

- Definition

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-URI http://asc.fasb.org/topic&trid=49130388

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130551-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130556-203045

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130550-203045

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130558-203045

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130554-203045

+ Details

Net Loss Per Common Share

6 Months Ended

Jun. 30, 2020

Earnings Per Share [Abstract]

Net Loss Per Common Share

11. 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 June 30, 2020 and 2019 and for the six months ended June 30, 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 June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
	(unaudited)				(unaudited)
Stock options issued and outstanding		6,657,569		5,212,276		6,463,895		5,184,331

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

Related Party Transactions

6 Months Ended

Jun. 30, 2020

Related Party Transactions

12. Related party transactions

The Company maintained 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 expired on June 30, 2020. Effective July 1, 2020, the Company renewed its agreement with the member of the Board of Directors for scientific, clinical and regulatory advisory services outside of his role on the Board of Directors through June 30, 2021.

The Company granted an exclusive, worldwide, royalty-bearing license of its CDK2 inhibitor compounds to ARC Therapeutics, LLC (“ARC”), a company primarily owned by a related party, in exchange for cash and equity in ARC with a total value of approximately $2.1 million, which resulted in the recognition of related party revenue as discussed in Note 10.

Subsequent Events

6 Months Ended

Jun. 30, 2020

Subsequent Events [Abstract]

Subsequent Events

13. Subsequent events

On July 22, 2020, the Company entered into an exclusive, royalty-bearing license agreement with EQRx, Inc. to develop and commercialize lerociclib in the U.S., Europe, Japan and all other global markets, excluding the Asia-Pacific region (except Japan). The Company will receive an upfront cash payment of $20.0 million and will be eligible to receive development and commercial milestone payments of up to $290.0 million, plus tiered royalties ranging from mid-single digits to mid-teens based on annual net sales of lerociclib.

In August 2020, the Company entered into an exclusive license agreement with Nanjing Simcere Dongyuan Pharmaceutical Co., Ltd (“Simcere”) for development and commercialization rights for trilaciclib in all indications in Greater China (mainland China, Hong Kong, Macau, and Taiwan). Under the terms of the agreement, the Company will receive an upfront payment of $14.0 million and be eligible to receive up to $156.0 million in development and commercial milestone payments. Simcere will also pay the Company tiered low double-digit royalties on annual net sales of trilaciclib in Greater China. As part of this agreement, Simcere will participate in global clinical trials of trilaciclib and the companies will be responsible for all development and commercialization costs in their respective territories.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 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 June 30, 2020, and for the three and six months ended June 30, 2020 and 2019, is unaudited. The results for the six months ended June 30, 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. Certain amounts have been reclassified to conform to current presentation.
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.
Revenue Recognition	Revenue Recognition For elements of those arrangements that we determine should be accounted for under ASC 606, Revenue from Contracts with Customers (“ASC 606”), we assess which activities in our license or collaboration agreements are performance obligations that should be accounted for separately and determine the transaction price of the arrangement, which includes the assessment of the probability of achievement of future milestones and other potential consideration. For arrangements that include multiple performance obligations, such as granting a license or performing manufacturing or research and development activities, we allocate the transaction price based on the relative standalone selling price and recognize revenue that is allocated to the respective performance obligation when (or as) control is transferred to the customer and the performance obligation is satisfied. Accordingly, we develop assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. These key assumptions may include revenue forecasts, clinical development timelines and costs, discount rates and probabilities of clinical and regulatory success. Licenses of intellectual property If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue associated with the bundled performance obligation. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of progress and related revenue recognition. Milestone Payments At the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. The Company evaluates each milestone to determine when and how much of the milestone to include in the transaction price. The Company first estimates the amount of the milestone payment that the Company could receive using either the expected value or the most likely amount approach. The Company primarily uses the most likely amount approach as that approach is generally most predictive for milestone payments with a binary outcome. Then, the Company considers whether any portion of that estimated amount is subject to the variable consideration constraint (that is, whether it is probable that a significant reversal of cumulative revenue would not occur upon resolution of the uncertainty). The Company updates the estimate of variable consideration included in the transaction price at each reporting date which includes updating the assessment of the likely amount of consideration and the application of the constraint to reflect current facts and circumstances. Royalties For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any revenue related to sales-based royalties or milestone payments based on the level of sales.
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 six months ended June 30, 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 June 30, 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 June 30, 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.
Debt Issuance cost	Debt Issuance Costs Debt issuance costs are amortized to interest expense over the estimated life of the related debt based on the effective interest method. In accordance with ASC 835, Interest, we present debt issuance costs on the condensed balance sheet as a direct deduction from the associated debt.
Coronavirus (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. Initiation of two clinical trials, the rintodestrant/palbociclib combination trial and the I-SPY 2 trial, began in the second quarter of 2020 as scheduled. 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.

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2020

Fair Value Disclosures [Abstract]

Summary of Financial Instruments and Respective Fair Values

At June 30, 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 June 30, 2020
Assets
Money market funds	$	216,815	$	—	$	—	$	216,815
Certificates of Deposit		15,957		—		—		15,957
Total assets at fair value:	$	232,772	$	—	$	—	$	232,772

	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)

6 Months Ended

Jun. 30, 2020

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

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

	June 30, 2020			December 31, 2019

Computer equipment		330			332
Laboratory equipment		862			871
Furniture and fixtures		1,071			1,071
Leasehold improvements		1,941			1,941
Accumulated depreciation		(991	)		(677	)
Property and equipment, net	$	3,213		$	3,538

Accrued Expenses (Tables)

6 Months Ended

Jun. 30, 2020

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses are comprised as follows (in thousands):

	June 30, 2020		December 31, 2019

Accrued external research	$	2,206	$	2,737
Accrued professional fees and other		7,527		1,487
Accrued external clinical study costs		6,764		7,996
Accrued compensation expense		1,809		3,183
Accrued expenses	$	18,306	$	15,403

Loan Payable (Tables)

6 Months Ended

Jun. 30, 2020

Debt Disclosure [Abstract]

Schedule of Outstanding Debt Obligations

As of June 30, 2020 the future principal payments due under the Loan Agreement, excluding interest, are as follows:

	Amount

Remainder of 2020	$	—
2021		—
2022		4,631
2023		9,972
2024		5,397
Total principal outstanding		20,000
End of term charge		56
Unamortized debt issuance costs		(603	)
Total		19,453

Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 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:

	June 30, 2020		December 31, 2019

Common stock options outstanding		6,539,518		5,744,036
Options available for grant under Equity Incentive Plans		1,239,003		938,738
		7,778,521		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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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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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+ Details

Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2020

Summary of Stock Option Activity

Stock option activity for the six months ended June 30, 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		(506,749	)	$	32.74
Granted		1,603,037			18.35
Exercised		(300,806	)		4.84
Balance as of June 30, 2020		6,539,518		$	16.57		7.6	$	65,133
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 June 30, 2020		3,290,661			10.61		6.1	$	51,632
Vested at June 30, 2020 and expected to vest		6,539,518			16.57		7.6	$	65,133

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 six months ended June 30, 2020 and June 30, 2019:

	Three Months Ended June 30,		Six Months Ended June 30,
	2020	2019	2020		2019

Expected volatility	78.5 - 79.7%	74.2 - 77.0%	74.8 - 79.7%		74.2 - 82.1%
Weighted-average risk free rate	0.4%	1.9 - 2.4%	0.4 - 1.7%		1.9 - 2.6%
Dividend yield	—%	—%	—%		—%
Expected term (in years)	5.68	5.82		6.01	6.0

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 June 30,				Six Months Ended June 30,
	2020		2019		2020		2019

Research and development	$	1,834	$	1,507	$	3,634	$	3,002
General and administrative		2,533		2,234		5,460		4,543
Total stock-based compensation expense	$	4,367	$	3,741	$	9,094	$	7,545

Net Loss Per Common Share (Tables)

6 Months Ended

Jun. 30, 2020

Earnings Per Share [Abstract]

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

For the three months ended June 30, 2020 and 2019 and for the six months ended June 30, 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 June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
	(unaudited)				(unaudited)
Stock options issued and outstanding		6,657,569		5,212,276		6,463,895		5,184,331

Business Description - Additional Information (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($) Product
Description Of Business [Line Items]
Number of clinical-stage product candidates from pipeline \| Product	3
Simcere License Agreement
Description Of Business [Line Items]
Upfront payments along with sales based royalties	$ 14.0
Milestone payments	156.0
EQRx License Agreement
Description Of Business [Line Items]
Upfront payments along with sales based royalties	26.0
Milestone payments	330.0
ARC License Agreement
Description Of Business [Line Items]
Upfront payments along with equity in ARC	$ 2.1

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details)	6 Months Ended
	Jun. 30, 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 \| Trial	2

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Fair Value Measurements - Summary of Financial Instruments and Respective Fair Values (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets
Assets at fair value	$ 232,772	$ 268,436
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Assets at fair value	232,772	268,436
Money Market Funds
Assets
Assets at fair value	216,815	252,563
Money Market Funds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Assets at fair value	216,815	252,563
Certificates of Deposit
Assets
Assets at fair value	15,957	15,873
Certificates of Deposit \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Assets at fair value	$ 15,957	$ 15,873

Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Changes in valuation methodology	$ 0	$ 0	$ 0

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Accumulated depreciation	$ (991)	$ (677)
Property and equipment, net	3,213	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	862	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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Property Plant And Equipment [Abstract]
Depreciation expenses relating to property and equipment	$ 158	$ 65	$ 317	$ 129

Patent License Agreement - Additional Information (Details) - USD ($)	3 Months Ended			6 Months Ended		43 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2016	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020
Patent License Agreement [Line Items]
Non-refundable license issue fee	$ 18,531,000	$ 23,489,000		$ 38,965,000	$ 41,569,000
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	Jun. 30, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued external research	$ 2,206	$ 2,737
Accrued professional fees and other	7,527	1,487
Accrued external clinical study costs	6,764	7,996
Accrued compensation expense	1,809	3,183
Accrued expenses	$ 18,306	$ 15,403

Loan Payable - Additional Information (Details) - USD ($) $ in Thousands		6 Months Ended
	May 29, 2020	Jun. 30, 2020
Debt Instrument [Line Items]
Loan amount		$ 19,453
Loan net carrying amount		$ 20,000
Loan Agreement \| Hercules Capital, Inc.
Debt Instrument [Line Items]
Loan amount	$ 20,000
Earliest maturity date		Jun. 01, 2022
Latest maturity date		Jan. 01, 2023
Debt instrument maturity date description		Following the interest only period, the Company will repay the principal balance and interest of the advances in equal monthly installments through June 1, 2024
Interset rate description		greater of either (i) (a) the prime rate as reported in The Wall Street Journal, plus (b) 6.40%, and (ii) 9.65%
Loan agreement, basis spread on variable rate		6.40%
Loan agreement, interest rate, stated percentage		9.65%
Prepayment fee description		(a) 3.0% of the prepayment amount in the first year; (b) 2.0% of the prepayment amount in the second year; and (b) 1.0% of the prepayment amount in the third year.
Percentage of prepayment of loan amount for year first		3.00%
Percentage of prepayment of loan amount for year second		2.00%
Percentage of prepayment of loan amount for year third		1.00%
Percentage of loan amount prepayment charge		6.95%
Loan agreement, issuance costs		$ 400
Loan Agreement \| Hercules Capital, Inc. \| First Tranche
Debt Instrument [Line Items]
Loan amount	30,000
Milestone payments	20,000
End of term fee		$ 2,100
Percentage of aggregate amount of all loan advances payment		6.95%
Loan net carrying amount		$ 19,400
Loan Agreement \| Hercules Capital, Inc. \| First Tranche \| Other Income (Expense)
Debt Instrument [Line Items]
Interest expense, loan agreement		300
Loan Agreement \| Hercules Capital, Inc. \| Second Tranche
Debt Instrument [Line Items]
Loan amount	20,000
Loan Agreement \| Hercules Capital, Inc. \| Third Tranche
Debt Instrument [Line Items]
Loan amount	30,000
Loan Agreement \| Hercules Capital, Inc. \| Fourth Tranche
Debt Instrument [Line Items]
Loan amount	$ 20,000
Loan Agreement \| Hercules Capital, Inc. \| Maximum
Debt Instrument [Line Items]
Loan amount		$ 100,000

Loan Payable - Schedule Future Principal Payments Due Under Loan Agreement Excluding Interest (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($)
Debt Disclosure [Abstract]
2022	$ 4,631
2023	9,972
2024	5,397
Total principal outstanding	20,000
End of term charge	56
Unamortized debt issuance costs	(603)
Loan amount	$ 19,453

Stockholders' Equity - Additional Information (Details) - shares	6 Months Ended
	Jun. 30, 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	Jun. 30, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance	7,778,521	6,682,774
Common Stock Options Outstanding
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance	6,539,518	5,744,036
Options Available For Grant Under Equity Incentive Plan
Class Of Stock [Line Items]
Common stock, shares reserved for future issuance	1,239,003	938,738

Stock-Based Compensation - Additional Information (Details) - shares		6 Months Ended
	Jan. 01, 2020	Jun. 30, 2020	May 31, 2017
Employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options, maximum term		10 years
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
Number of additional shares approved for grant under equity incentive plan	1,096,553
Number of shares available for grant under equity incentive plan		1,239,003
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

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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	78.50%	74.20%	74.80%	74.20%
Expected volatility, maximum	79.70%	77.00%	79.70%	82.10%
Weighted-average risk free rate	0.40%
Weighted-average risk free rate, minimum		1.90%	0.40%	1.90%
Weighted-average risk free rate, maximum		2.40%	1.70%	2.60%
Expected term (in years)	5 years 8 months 4 days	5 years 9 months 25 days	6 years 3 days	6 years

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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 4,367	$ 3,741	$ 9,094	$ 7,545
Research and development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	1,834	1,507	3,634	3,002
General and administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 2,533	$ 2,234	$ 5,460	$ 4,543

Stock-Based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Options outstanding
Beginning balance \| shares	5,744,036
Cancelled \| shares	(506,749)
Granted \| shares	1,603,037
Exercised \| shares	(300,806)
Ending balance \| shares	6,539,518	5,744,036
Exercisable \| shares	3,290,661	3,001,179
Vested and expected to vest \| shares	6,539,518	5,744,036
Weighted average exercise price
Beginning balance \| $ / shares	$ 16.88
Cancelled \| $ / shares	32.74
Granted \| $ / shares	18.35
Exercised \| $ / shares	4.84
Ending balance \| $ / shares	16.57	$ 16.88
Exercisable \| $ / shares	10.61	8.93
Vested and expected to vest \| $ / shares	$ 16.57	$ 16.88
Weighted average, Remaining contractual for life (Years)
Balance	7 years 7 months 6 days	7 years 6 months
Exercisable	6 years 1 month 6 days	6 years 1 month 6 days
Vested and expected to vest	7 years 7 months 6 days	7 years 6 months
Weighted average, Aggregate intrinsic value
Balance \| $	$ 65,133	$ 72,251
Exercisable \| $	51,632	58,797
Vested and expected to vest \| $	$ 65,133	$ 72,251

License Revenue - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
	May 22, 2020	Jun. 30, 2020	Jun. 30, 2020	Jun. 15, 2020
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
License revenue recognized		$ 2,140	$ 2,140
ARC Therapeutics, LLC
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Upfront payment received	$ 1,000
Percentage of equity interest received as consideration	10.00%
Milestone payments receivable	$ 2,000
License revenue recognized	$ 2,100		2,100
Equity interest	10.00%
Genor Biopharma Co. Inc.
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Upfront payment received			0
Milestone payments receivable				$ 40,000
Non-refundable, upfront payment				6,000
Amount owed upon the delivery of existing inventory				$ 600
Amount of remaining performance obligations to be recognized as revenue by period		$ 0	$ 0

Net Loss Per Common Share - Schedule of Potentially Dilutive Securities Excluded from Computations of Diluted Weighted-average Shares Outstanding (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
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	6,657,569	5,212,276	6,463,895	5,184,331

Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
	May 22, 2020	Jun. 30, 2020	Jun. 30, 2020
Related Party Transaction [Line Items]
License revenue - related party		$ 2,140	$ 2,140
ARC License Agreement
Related Party Transaction [Line Items]
License revenue - related party	$ 2,100		$ 2,100
Scientific Advisory \| Chairman of the Board of Directors
Related Party Transaction [Line Items]
Consulting agreement expiration date			Jun. 30, 2020
Scientific Clinical and Regulatory Advisory \| Chairman of the Board of Directors
Related Party Transaction [Line Items]
Consulting agreement expiration date			Jun. 30, 2021

- Definition

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130545-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130543-203045

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9031-108599

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

+ Details

Subsequent Events (Detail) - Subsequent Event - USD ($) $ in Millions	Aug. 31, 2020	Jul. 22, 2020
Simcere License Agreement
Subsequent Event [Line Items]
Upfront cash payment received	$ 14.0
Maximum \| Simcere License Agreement
Subsequent Event [Line Items]
Milestone payments receivable	$ 156.0
EQRx License Agreement
Subsequent Event [Line Items]
Upfront cash payment received		$ 20.0
EQRx License Agreement \| Maximum
Subsequent Event [Line Items]
Milestone payments receivable		$ 290.0