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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2019	Feb. 21, 2020	Jun. 30, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
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 $.0001 par value
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
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 Annual Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		37,642,199
Entity Public Float			$ 853,358,707
Documents Incorporated by Reference	Documents Incorporated by Reference Portions of the Registrant’s Definitive Proxy Statement relating to the Annual Meeting of Stockholders, scheduled to be held on June 11, 2020, are incorporated by reference into Part III of this report.

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 269,208	$ 369,290
Restricted cash	63
Prepaid expenses and other current assets	1,732	843
Total current assets	271,003	370,133
Property and equipment, net	3,538	1,137
Restricted cash	437
Operating lease assets	9,853
Total assets	284,831	371,270
Current liabilities
Accounts payable	3,684	3,377
Accrued expenses	15,403	8,985
Other current liabilities	682
Total current liabilities	19,769	12,362
Operating lease liabilities	9,535
Other non-current liabilities		88
Total liabilities	29,304	12,450
Commitments and contingencies
Stockholders’ equity
Common stock, $0.0001 par value, 120,000,000 shares authorized as of December 31, 2019 and December 31, 2018, respectively; 37,638,260 and 37,268,792 shares issued as of December 31, 2019 and December 31, 2018, respectively; 37,611,594 and 37,242,126 shares outstanding as of December 31, 2019 and December 31, 2018, respectively	4	4
Treasury stock, 26,666 shares	(8)	(8)
Additional paid-in capital	592,384	573,230
Accumulated deficit	(336,853)	(214,406)
Total stockholders’ equity	255,527	358,820
Total liabilities and stockholders' equity	$ 284,831	$ 371,270

Statements of Operations - USD ($) $ in Thousands	12 Months Ended
Statements of Operations - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenue from Contract with Customer, Product and Service [Extensible List]	us-gaap:GrantMember	us-gaap:GrantMember	us-gaap:GrantMember
Operating expenses
Research and development	$ 89,002	$ 70,683	$ 53,881
General and administrative	40,039	18,603	7,087
Total operating expenses	129,041	89,286	60,968
Operating loss	(129,041)	(89,286)	(60,968)
Other income (expense)
Other income	6,594	3,998	888
Change in fair value in warrant liability and other liabilities			(41)
Total other income, net	6,594	3,998	847
Net loss	(122,447)	(85,288)	(60,121)
Accretion of redeemable convertible preferred stock			(4,757)
Net loss attributable to common stockholders	$ (122,447)	$ (85,288)	$ (64,878)
Net loss per share attributable to common stockholders, basic and diluted	$ (3.27)	$ (2.56)	$ (3.57)
Weighted average common shares outstanding, basic and diluted	37,499,256	33,316,719	18,197,970

Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series C Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock	Series A Redeemable Convertible Preferred Stock	Series 1 Redeemable Convertible Preferred Stock	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2016	$ (64,993)						$ (8)		$ (64,985)
Temporary equity, balance (in shares) at Dec. 31, 2016		5,609,398	7,642,734	4,998,895	682,026
Temporary equity, balance at Dec. 31, 2016		$ 51,424	$ 40,355	$ 14,431	$ 1,370
Balance (in shares) at Dec. 31, 2016						1,504,947	(26,666)
Temporary equity accretion of redeemable, convertible preferred stock		3,732	620	235	171
Accretion of redeemable, convertible preferred stock	(4,757)							$ (745)	(4,012)
Initial public offering	108,503					$ 1		108,502
Initial public offering (in shares)						7,781,564
Automatic conversion of preferred stock	112,337	$ (55,156)	$ (40,975)	$ (14,666)	$ (1,541)	$ 2		112,335
Automatic conversion of preferred stock, in shares		(5,609,398)	(7,642,734)	(4,998,895)	(682,026)	18,933,053
Automatic conversion of preferred warrants	208							208
Exercise of common stock options	214							214
Exercise of common stock options (in shares)						160,579
Exercise of common stock warrants	1							1
Exercise of common stock warrants, in shares						40,368
Stock-based compensation	3,394							3,394
IPO/Stock financing costs	(1,398)							(1,398)
Net loss during year	(60,121)								(60,121)
Balance at Dec. 31, 2017	93,388					$ 3	$ (8)	222,511	(129,118)
Balance (in shares) at Dec. 31, 2017						28,420,511	(26,666)
Public offering (Follow-on Financings)	303,522					$ 1		303,521
Public offering (Follow-on Financings), shares						7,360,000
Public offering (ATM)	36,068							36,068
Public offering (ATM), shares						752,008
Exercise of common stock options	1,797							1,797
Exercise of common stock options (in shares)						736,273
Stock-based compensation	10,225							10,225
IPO/Stock financing costs	(892)							(892)
Net loss during year	(85,288)								(85,288)
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	$ 2,705							2,705
Exercise of common stock options (in shares)	369,468					369,468
Stock-based compensation	$ 16,449							16,449
Net loss during year	(122,447)								(122,447)
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)

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net loss	$ (122,447)	$ (85,288)	$ (60,121)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	356	175	89
Stock-based compensation	16,449	10,225	3,394
Gain/loss on disposal of property and equipment		8	6
Increase in fair value of warrant activity			41
Change in operating assets and liabilities
Prepaid expenses and other assets	(219)	113	(253)
Accounts payable	248	(1,002)	1,578
Accrued Expenses	6,042	1,446	4,709
Deferred Rent		16	38
Net cash used in operating activities	(99,571)	(74,307)	(50,519)
Cash flows from investing activities
Purchases of property and equipment	(2,716)	(709)	(294)
Net cash used in investing activities	(2,716)	(709)	(294)
Cash flows from financing activities
Proceeds from stock options and warrants exercised	2,705	1,797	215
Proceeds from public offering, net of underwriting fees and commissions		339,589	108,503
Payment of public offering costs		(892)	(1,398)
Net cash provided by financing activities	2,705	340,494	107,320
Net change in cash, cash equivalents and restricted cash	(99,582)	265,478	56,507
Cash, cash equivalents and restricted cash
Beginning of period	369,290	103,812	47,305
End of period	269,708	369,290	103,812
Non-cash investing and financing activities
Upfront project costs and other current assets in accounts payable and accrued expenses	43	107
Accretion of redeemable convertible preferred stock			4,757
Purchases of equipment in accounts payable and accrued expenses	41	$ 100
Conversion of preferred stock and preferred warrants to common stock and common warrants			$ 112,545
Operating lease liabilities arising from obtaining right-of-use asset	$ 8,947

Description of Business

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Description of Business

1. Description of business

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 (formerly known as G1T48) is a potential best-in-class oral selective estrogen receptor degrader (SERD) for the treatment of ER+ breast cancer. Lerociclib is a differentiated oral CDK4/6 inhibitor designed to enable more effective combination treatment strategies across multiple oncology indications, including estrogen receptor-positive, HER2-negative (ER+, HER2-) breast cancer. The Company also has an active discovery program focused on cyclin-dependent kinase targets. The Company owns the global rights to all of its product candidates.

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. Based on written feedback from its pre-New Drug Application (NDA) meeting with the FDA, the Company began a rolling NDA submission for trilaciclib for myelopreservation in SCLC in the fourth quarter of 2019 and expects to complete the NDA submission in the second quarter of 2020. Based on discussions with European regulatory authorities, the Company plans to submit a Marketing Authorization Application (MAA) to the European Medicines Agency (EMA) for trilaciclib for myelopreservation in SCLC in the second half of 2020. 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 ~50% more cycles of chemo, 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 will be 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, 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 in colorectal cancer in the fourth quarter of 2020.

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. We have completed enrollment of the dose escalation and dose expansion portions of the trial and expect to initiate 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 we 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. In 2018, the Company reported encouraging preliminary Phase 1b data from its Phase 1/2 trial in ER+, HER2- breast cancer (in combination with fulvestrant) and will report additional Phase 1b/2a data from this trial at the San Antonio Breast Cancer Symposium on December 11, 2019. The Company also initiated a Phase 1b/2 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. The Company is currently exploring partnering opportunities to continue to advance clinical development of lerociclib.

The Company’s financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business. As of December 31, 2019, the Company had an accumulated deficit of $336.9 million. The Company has reported a net loss in all fiscal periods since inception and expects to incur substantial losses in the future to conduct research and development and pre-commercialization activities.

As of December 31, 2019, the Company had cash and cash equivalents of $269.2 million. The Company expects that its existing cash and cash equivalents will enable it to fund its operating expenses and capital expenditure requirements for greater than 12 months from the date of filing this Annual Report.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of significant accounting policies

Basis of presentation

The Company has prepared the accompanying financial statements in conformity with generally accepted accounting principles in the United States of America (“U.S. GAAP”).

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. Actual results could differ from those estimates. These estimates include the Company’s common stock valuation, stock compensation, warrant valuation and deferred tax asset valuation allowance.

Cash and cash equivalents

The Company considers all highly liquid investments purchased with an original maturity of three months or less at the date of purchase to be cash equivalents. Cash and cash equivalents at December 31, 2019 and 2018 consist of amounts on deposit in banks, including checking accounts, money market accounts and certificates of deposit. Cash deposits are all in financial institutions in the United States. As part of the lease for the new office space, the Company obtained a standby letter of credit in the amount of $0.5 million related to the security deposit. This letter of credit is secured by money market funds at the financial institution. Therefore, these funds are classified as restricted cash on the balance sheet. The letter of credit will be reduced ratably on each anniversary of the commencement of the lease until the end of the lease term.

Concentration of credit risk

Financial instruments that potentially subject the Company to credit risk consist of cash and cash equivalents. Deposits with financial institutions are insured, up to certain limits, by the Federal Deposit Insurance Corporation (“FDIC”). The Company’s cash deposits often exceed the FDIC insurance limit; however, all deposits are maintained with high credit quality institutions and the Company has not experienced any losses in such accounts. The financial condition of financial institutions is periodically reassessed, and the Company believes the risk of any loss is minimal. The Company believes the risk of any loss on cash due to credit risk is minimal.

Property and equipment

Property and equipment are stated at cost less accumulated depreciation. Depreciation is generally calculated using the straight-line method over the following estimated useful lives:

Computer equipment			5 years
Laboratory equipment			5 years
Furniture and fixtures			7 years
Leasehold improvements			7 years

Costs associated with maintenance and repairs are charged to expense as incurred. Property and equipment held under leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the related asset.

Impairment of long-lived assets

The Company evaluates its long-lived assets for indicators of possible impairment by comparison of the carrying amounts to future net undiscounted cash flows expected to be generated by such assets when events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. Should an impairment exist, the impairment loss would be measured based on the excess carrying value of the asset over the asset’s fair value based on discounted estimates of future cash flows. For the years ended December 31, 2019, 2018 and 2017, the Company’s management evaluated its long-lived assets and determined no impairment charge was needed.

Warrant liability

Warrants to purchase the Company’s redeemable convertible preferred stock were classified as liabilities and recorded at their estimated fair value. In each reporting period, any change in fair value of the warrants has been recorded as expense in the case of an increase in fair value and income in the case of a decrease in fair value.

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 involved 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.

Fair value of financial instruments

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 December 31, 2019 and 2018 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 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

	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, 2018
Assets
Money market funds	$	352,934	$	—	$	—	$	352,934
Certificates of Deposit		15,501		—		—		15,501
Total assets at fair value:	$	368,435	$	—	$	—	$	368,435

Patent costs

Costs associated with the submission of patent applications are expensed as incurred given the uncertainty of the future economic benefits of the patents. Patent-related legal expenses included in general and administrative costs were approximately $2,114 thousand, $1,352 thousand, and $997 thousand for the years ended December 31, 2019, 2018 and 2017, respectively.

Income taxes

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 December 31, 2019 and 2018, 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 December 31, 2019 and 2018, the Company had no such accruals.

Stock-based compensation

The primary type of stock-based payments utilized by the Company are stock options. The Company accounts for stock-based employee compensation arrangements by measuring the cost of employee services received in exchange for all equity awards granted based on the fair value of the award on the grant date. The fair value of each employee stock option is estimated on the date of grant using an options pricing model. The Company currently uses the Black-Scholes valuation model to estimate the fair value of its share-based payments. The model requires management to make a number of assumptions including expected volatility, expected life, risk-free interest rate and expected dividends.

The Company accounts for stock-based non-employee compensation arrangements by recording the expense of such services based on the fair value of the equity instrument as estimated using the Black-Scholes pricing model. The fair value of the equity instrument is charged to operating expense over the term of the service agreement. In accordance with the implementation of ASU No. 2018-07 on January 1, 2019, the fair value of non-employee stock options is no longer be re-measured each reporting period.

Segment information

The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. All of the Company’s assets are held in the United States.

Comprehensive loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. There was no difference between net loss and comprehensive loss for each of the periods presented in the accompanying financial statements.

Redeemable convertible preferred stock

The Company classifies its redeemable convertible preferred stock, for which the Company does not control the redemption, outside of permanent equity. The Company records redeemable convertible preferred stock at fair value upon issuance, net of any offering costs, and the carrying value is adjusted to the redemption value at the end of each reporting period. These adjustments are effected through charges against additional paid-in capital and accumulated deficit.

Leases

We determine if an arrangement is a lease at inception. Operating lease assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. Operating leases are included in operating lease assets, other current liabilities, and operating lease liabilities on our balance sheet at December 31, 2019. Operating lease assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at commencement date to determine the present value of future payments. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term.

Prior period amounts continue to be reported in accordance with our historic accounting under previous lease guidance, Topic 840. See “Adoption of New Accounting Standards – Impact of Adoption of Topic 842” below, for more information about the impact of the adoption of Topic 842.

Recent Accounting Pronouncements

Adoption of New Accounting Standards

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”). This guidance revises the accounting related to leases by requiring lessees to recognize a lease liability and a right-of-use asset for all leases. In January 2019, the Company adopted ASU 2016-02 using the modified retrospective transition method with an effective date as of the beginning of our fiscal year, January 1, 2019. Prior period amounts have not been adjusted and continue to be reported in accordance with our historical reporting under previous lease guidance, ASC Topic 840. As part of the adoption, we have elected to account for separate lease and associated non-lease components as a single lease component for our real estate leases.

In June 2018, the FASB issued ASU No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”). ASU 2018-07 expands the scope of Topic 718, Compensation – Stock Compensation, to include share-based payments issued to non-employees for goods or services. Consequently, non-employees and employees will be substantially aligned. ASU 2018-07 supersedes Subtopic 505-50, Equity – Equity-Based Payments to Non-Employees. The amendments are effective for fiscal years beginning after December 15, 2018. Early adoption is permitted, but not earlier than the adoption of Topic 606, Revenue from Contracts with Customers. The Company adopted ASU 2018-07 on January 1, 2019. The adoption of this standard did not have a material impact on the Company’s financial statements.

Impact of Adoption of Topic 842

With the adoption of Topic 842 on January 1, 2019, the Company recognized operating lease assets and operating lease liabilities of $1.5 million and $1.6 million, respectively, with the difference due to the de-recognition of current and non-current deferred rent. There was no impact to the opening accumulated deficit as of January 1, 2019.

The impact of the adoption of Topic 842 on the accompanying balance sheet as of January 1, 2019 was as follows (in thousands):


	December 31, 2018		Adjustments Due to the Adoption of Topic 842			January 1, 2019

Operating lease assets	$	—	$	1,533		$	1,533
Accrued expenses		8,985		(9	)		8,976
Operating lease liabilities:
Other current liabilities		—		352			352
Non-current operating lease liabilities		—		1,278			1,278
Other non-current liabilities		88		(88	)		—
Stockholders' equity		358,820		—			358,820

Recently Issued 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. ASU 2018-15 is effective for annual and interim reporting periods beginning after December 15, 2019, and early adoption is permitted. The amendments under ASU 2018-15 may be applied either retrospectively or prospectively to all implementation costs incurred after adoption. The Company is evaluating the impact of ASU 2018-15 on its financial statements and the timing of adoption.

Leases

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Leases

6. Leases

As described in our “Note 2. Basis of Presentation and Summary of Significant Accounting Policies”, we adopted Topic 842 as of January 1, 2019. Prior period amounts have not been adjusted and continue to be reported in accordance with our historic accounting under Topic 840.

Pursuant to a lease agreement dated January 10, 2014 (the “Lease”), on April 1, 2014, the Company leased office and lab space with a free rent period and escalating rent payments; the Lease had an expiration date of July 31, 2017. The Lease was amended on January 27, 2016 to lease new larger office and lab space beginning in August 2016 with a discounted rent period and escalating rent payments and the Lease term was extended to December 31, 2022. The amendment also contained an option for a five-year renewal and a right of first refusal to lease adjacent office space. The Lease was further amended on March 27, 2017 to lease additional office space beginning in August 2017 with a discounted rent period and escalating rent payments. The Lease was amended again in January 2018 to lease additional adjacent office space beginning in August 2018 with a discounted rent period and escalating rent payments. The term of the renewal option contained in the Lease, as amended, was not included in the measurement of the operating lease asset and liability since exercise of the option was uncertain.

In November 2018, the Company signed a new lease to secure approximately 60,000 square feet of laboratory and office space at 700 Park Offices Drive in Research Triangle Park, NC (“700 Lease”). The 700 Lease commenced on September 2, 2019 and has an expiration date of September 30, 2027 for the initial term with the Company having the option to renew for an additional 5 years. The term of the renewal option contained in the Lease was not included in the measurement of the operating lease asset and liability since exercise of the option was uncertain. As part of the 700 Lease, the Company obtained a standby letter of credit in the amount of $0.5 million related to the security deposit. This letter of credit is secured by money market funds at the financial institution. Therefore, these funds are classified as restricted cash on the balance sheet. The letter of credit will be reduced ratably on each anniversary of the commencement of the 700 Lease until the end of the lease term.

The tables below reflect the Company’s lease position and weighted-average lease terms and discount rates for our operating leases as of December 31, 2019. Operating lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. In determining the present value of lease payments, we use our incremental borrowing rate based on the information available at the lease commencement date.


(in thousands)	Classification on the Balance Sheet	December 31, 2019
Assets
Operating lease assets	Operating lease assets	$	9,853
Total lease assets		$	9,853

Liabilities
Current
Operating	Other current liabilities	$	682
Non-current
Operating	Operating lease liabilities		9,535
Total lease liabilities		$	10,217

Lease Term and Discount Rate	December 31, 2019
Weighted-average remaining lease term (years)
Operating leases		7.2
Weighted-average discount rate
Operating leases		7.7	%

The table below presents information related to the lease costs for operating leases (in thousands):


		Year Ended December 31,
(in thousands)	Classification	2019		2018		2017

Operating lease costs (a)	Research and development	$	609	$	298	$	207
	General and administrative		368		83		45
Total operating lease costs		$	977	$	381	$	252
(a) Includes variable lease costs which are immaterial.

The table below reconciles the undiscounted cash flow for each of the first five years and total of the remaining years to the operating lease liabilities recorded on the balance sheet as of December 31, 2019 (in thousands):

	Operating leases
Years ending December 31,
2020		1,459
2021		2,015
2022		2,072
2023		1,634
2024		1,679
Thereafter		4,855
Total future minimum lease payments	$	13,714
Less: present value adjustment		(3,497	)
Total operating lease liabilities	$	10,217

Cash payments included in the measurement of our operating leases were $688 thousand for the twelve months ended December 31, 2019.

ASC 840 Disclosures

The Company elected the alternative modified transition method and included the following table previously disclosed.

The following is a schedule by years of minimum future rental payments on noncancelable operating leases as of December 31, 2018 (in thousands):

2019	$	680
2020		1,427
2021		1,960
2022		2,015
2023		1,577
2024 and thereafter		6,155
	$	13,814

Stockholders’ Equity

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Stockholders’ Equity

7. Stockholders’ Equity

Redeemable convertible preferred stock

The Company has determined that the Series C, Series B, Series A and Series 1 redeemable convertible preferred stock were redeemable, after a stated period of time, based on voting thresholds that vary by stockholder class, as outlined in the Company’s certificate of incorporation. The Company classified its redeemable convertible preferred stock outside of permanent equity and into mezzanine equity.

The Company recorded its redeemable convertible preferred stock at fair value upon issuance, net of any issuance costs or discounts, and the carrying value is increased by periodic accretion to its redemption value until the earliest possible date of redemption. These increases were recorded as charges against additional paid-in-capital until the additional paid-in-capital balance is reduced to zero. At that time, additional accretion adjustments were recorded as additions to accumulated deficit.

In April 2016, the Company’s Board of Directors and stockholders approved the Fifth Amended and Restated Certification of Incorporation which increased the authorized number of shares of its redeemable convertible preferred stock to 57,108,717, of which 2,112,025 were be designated as Series 1 redeemable convertible preferred stock, 14,996,692 as Series A redeemable convertible preferred stock, 23,000,000 as Series B redeemable convertible preferred stock and 17,000,000 as Series C redeemable convertible preferred stock. In the second quarter of 2016, the Company authorized 16,828,217 shares of its Series C redeemable convertible preferred stock and issued 5,609,398 shares of its Series C redeemable convertible preferred stock for cash consideration at a price of $8.91 per share. Total additional proceeds amounted to $50.0 million.

Prior to the IPO, the holders of the Company’s convertible preferred stock had certain voting and dividend rights, as well as liquidation preferences and conversion privileges. All rights, preferences and privileges associated with the convertible preferred stock were terminated at the time of the Company’s IPO in conjunction with the conversion of all outstanding shares of convertible preferred stock into shares of common stock.

On May 22, 2017, the Company closed its IPO of 7,781,564 shares of the Company’s common stock at a public offering price of $15.00 per share, including 781,564 shares of common stock issued upon exercise by the underwriters of their option to purchase additional shares. The gross proceeds from the IPO were $116.7 million and net proceeds were $107.1 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company.

Upon closing of the IPO, all outstanding shares of the Company’s preferred stock were automatically converted into 18,933,053 shares of common stock. In connection with the IPO, the Board of Directors and the stockholders of the Company approved a one-for-three reverse stock split of the Company’s common stock. The reverse stock split became effective on May 11, 2017. All share and per share amounts in the financial statements have been retroactively adjusted for all periods presented to give effect to the reverse stock split, including reclassifying an amount equal to the reduction in par value to accumulated deficit.

Preferred stock

Upon completion of the IPO, all outstanding preferred stock was automatically converted into 18,933,053 shares of common stock. The Company is also authorized to issue 5,000,000 shares of undesignated preferred stock in one or more series. As December 31, 2019, no shares of preferred stock were issued or outstanding.

Common stock

The Company’s common stock has a par value of $0.0001 per share and consists of 120,000,000 authorized shares as of December 31, 2019 and 2018, respectively. Holders of common stock are entitled to one vote per share and are entitled to receive dividends, as if and when declared by the Company’s Board of Directors.

The Company has reserved authorized shares of common stock for future issuance at December 31, 2019 and December 31, 2018 as follows:

	December 31, 2019		December 31, 2018

Common stock options outstanding		5,744,036		4,502,133
Options available for grant under Equity Incentive Plans		938,738		1,547,306
		6,682,774		6,049,439

Stock option plan

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock option plan

8. Stock option plan

2011 Equity Incentive Plan

In March 2011, the Company adopted the 2011 Equity Incentive Plan (the “Plan”). As amended, 4,400,640 shares of common stock were reserved for issuance under the 2011 Plan. Eligible plan participants included employees, directors, officers, consultants and advisors of the Company. The 2011 plan permitted the granting of incentive stock options, nonqualified stock options and other stock- based awards. 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, 2018, and in accordance with the “evergreen” provision of the 2017 plan, an additional 1,066,692 shares were made available for issuance. Effective January 1, 2019, 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 December 31, 2019, there were a total of 938,738 shares of common stock available for future issuance under the 2017 Plan.

Stock-based Compensation

During the years ended December 31, 2019, 2018 and 2017, the Company recorded employee share-based compensation expense of $16,351, $8,157, and $1,772, respectively. The Company recorded non-employee share-based compensation expense of $98, $2,068, and $1,622 during the years ended December 31, 2019, 2018 and 2017, respectively. Total share-based compensation expense included in the statements of operations is as follows:

	Year Ended December 31,
	2019		2018		2017
	in thousands
Research and development	$	6,261	$	5,218	$	2,531
General and administrative		10,188		5,007		863
Total stock-based compensation expense	$	16,449	$	10,225	$	3,394

The fair value of each option grant is estimated on the grant date using the Black-Scholes option-pricing model, using the following weighted average assumptions:

	Year Ended December 31,
	2019		2018		2017

Expected volatility	74.2 - 82.1%		74.9 - 86.5%		74.2 - 79.3%
Weighted-average risk free rate	1.4 - 2.6%		2.3 - 3.0%		1.9 - 2.2%
Dividend yield	—%		—%		—%
Expected term (in years)	6.02		6.04		6.01
Weighted-average grant-date fair value per share	$	14.94	$	26.42	$	10.71

The expected term of stock options represents the weighted-average period the stock options are expected to remain outstanding and is based on the option vesting term, contractual terms and industry peers as the Company did not have sufficient historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior.

The expected stock price volatility assumptions for the Company’s stock options were determined by examining the historical volatilities for industry peers as the Company does not have sufficient history to estimate volatility using only its common stock. In 2019, the Company began incorporating its historical stock price in conjunction with selected similar publicly traded companies. The Company plans to continue to use the guideline peer group volatility information until the historical volatility of its common stock is sufficient to measure expected volatility for future option grants.

The risk-free interest rate assumption at the date of grant is based on the U.S. Treasury instruments whose term was consistent with the expected term of the Company’s stock options.

The expected dividend assumption is based on the Company’s history and expectation of dividend payouts.

Stock option activity during 2019 is as follows:

						Weighted average
				Weighted		Remaining
				average		contractual		Aggregate
	Options			exercise		for		intrinsic
	outstanding			price		life (Years)		value
								(in thousands)
Balance as of December 31, 2018		4,502,133		$	14.13		7.6	$	46,575
Cancelled		(326,654	)	$	20.49
Granted		1,938,025		$	22.06
Exercised		(369,468	)	$	7.32
Balance as of December 31, 2019		5,744,036		$	16.88		7.5	$	72,251
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

As of December 31, 2019, there was $42,049 of total unrecognized share-based compensation costs, which is expected to be recognized over a weighted-average period of 2.69 years.

Prior to our initial public offering, the fair value of our common shares underlying our stock options was estimated on each grant date by our board of directors. In order to determine the fair value of our common shares underlying granted stock options, our board of directors considered, among other things, timely valuations of our common shares prepared by an unrelated third-party valuation firm in accordance with the guidance provided by the American Institute of Certified Public Accountants Practice Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation.

Since the IPO, the board of directors has determined the fair value of each common share underlying share-based awards based on the closing price of the common shares as reported by Nasdaq on the date of grant.

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

10. Income taxes

In accordance with FASB 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 December 31, 2019 and 2018, 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 December 31, 2019 and 2018, the Company had no such accruals.

The components of income tax expense (benefit) attributable to continuing operations are as follows:

	Year ended December 31,
	2019		2018		2017
Current Expense:
Federal	$	—	$	—	$	—
State		—		—		—
		—		—		—
Deferred Expense:
Federal		—		—		—
State		—		—		—
	$	—	$	—	$	—

The differences between the company’s income tax expense attributable to continuing operations and the expense computed at the 21% U.S. statutory income tax rate were as follows (in thousands):

	Year ended December 31,
	2019			2018			2017
Federal income tax benefit at statutory rate:	$	(25,714	)	$	(17,910	)	$	(20,441	)
Increase (reduction) in income tax resulting from:
State Income Taxes		(2,369	)		(1,518	)		(1,623	)
Increase in Valuation Allowance		29,499			26,614			8,977
Write off Sec. 382 Limited Carryforwards		1,858			—			—
Equity Financing Expenses		—			—			39
Stock Compensation		461			(3,011	)		152
Research and Development Credit		(3,529	)		(4,187	)		(1,882	)
Effect on Tax Cuts & Job Acts Rate Reduction		—			—			14,770
Other		(206	)		12			8
	$	—		$	—		$	—

The tax effects of temporary differences and operating loss carryforwards that gave rise to significant portions of the deferred tax assets and deferred tax liabilities were as follows at December 31, 2019 and 2018 (in thousands):

	Year ended December 31,
	2019		2018
Deferred tax assets
Accrued expenses	$	2,205	$	1,413
Deferred rent		—		23
Operating lease liabilities		2,348		—
Stock compensation

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
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	37,638,260	37,268,792
Common stock, shares, outstanding	37,611,594	37,242,126
Treasury stock, shares	26,666	26,666