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Summary of Significant Accounting Policies - Summary of Number of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	4,120	3,225	3,060
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	4,080	3,186	2,233
Warrant
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	34	34	34
Employee Stock Purchase Plan Rights
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	6	5
Unvested Restricted Stock Awards
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities			793

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 26,135	$ 16,119
Short-term investments	210,756	162,866
Accounts receivable, related party	30	224
Prepaid expenses and other current assets	2,682	1,988
Total current assets	239,603	181,197
Property and equipment, net	44
Other long-term assets	2,325	1,182
Total assets	241,972	182,379
Current liabilities:
Accounts payable and accrued expenses	15,314	13,615
Current portion of long-term debt, net	250
Total current liabilities	15,564	13,615
Long-term debt, net	7,250	7,500
Other long-term liabilities	377	279
Total liabilities	23,191	21,394
Commitments and contingencies (Note 9)
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value; 200,000 shares authorized; 45,384 and 38,148 shares issued and outstanding as of December 31, 2019 and 2018, respectively	5	4
Additional paid-in capital	431,322	310,849
Accumulated other comprehensive income (loss)	331	(131)
Accumulated deficit	(212,877)	(149,737)
Total stockholders' equity	218,781	160,985
Total liabilities and stockholders' equity	$ 241,972	$ 182,379

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Research and development, related party	$ 432	$ 1,021	$ 1,312
General and administrative, related party	$ 325	$ 273	$ 247

Share-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	12 Months Ended
	Jan. 01, 2020	Mar. 31, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, subject to repurchase			0
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Closing price of common stock			$ 13.75
Unrecognized estimated stock option compensation expenses			$ 23.0
Weighted average service period			2 years 8 months 12 days
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of awards vested				$ 14.8	$ 12.7
Minimum \| Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			3 years
Maximum \| Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			4 years
Term of options to be granted under the Plan			10 years
2014 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of increase in common shares reserved for future issuance pursuant to future option grants			4.00%
Common shares reserved for future issuance pursuant to future option grants			800,835
2014 Plan \| Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			4 years
2014 Plan \| Restricted Stock With Cliff Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			1 year
2014 Plan \| Common Stock \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance			10,419,120
2014 Plan \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional common shares reserved for future issuance pursuant to future grants	1,815,361
2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional common shares reserved for future issuance pursuant to future grants			2,000,000
Common shares reserved for future issuance pursuant to future option grants			199,162
Percentage of maximum earnings withhold by employee to purchase shares		15.00%
Percentage of common stock purchase		85.00%
Cash received from exercise of ESPP purchase rights			$ 0.4	$ 0.1
Shares issued under ESPP			39,543
2015 Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of increase in common shares reserved for future issuance pursuant to future option grants			1.00%

Description of Business

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Description of Business

1. Description of Business

Kura Oncology, Inc., is a clinical-stage biopharmaceutical company committed to realizing the promise of precision medicines for the treatment of cancer. Our pipeline consists of small molecule product candidates that target cancer signaling pathways where there is a strong scientific and clinical rationale to improve outcomes, and we intend to pair them with molecular or cellular diagnostics to identify those patients most likely to respond to treatment. We plan to advance our product candidates through a combination of internal development and strategic partnerships while maintaining significant development and commercial rights.

References in these Notes to Financial Statements to “Kura Oncology, Inc.,” “we,” “our” or “us,” refer to Kura Oncology, Inc.

Commitments and Contingencies - Schedule of Supplemental Cash Flow Information Related to Operating Leases (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 485
ROU assets obtained in exchange for operating lease liabilities	472
Cambridge, MA
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	270
ROU assets obtained in exchange for operating lease liabilities	251
Araxes Pharma LLC
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	215
ROU assets obtained in exchange for operating lease liabilities	$ 221

License Agreements

12 Months Ended

Dec. 31, 2019

License Agreements [Abstract]

License Agreements

8. License Agreements

Janssen License Agreement

In December 2014, we entered into a license agreement with Janssen Pharmaceutica NV, or Janssen, which was amended in June 2016, under which we received certain intellectual property rights related to tipifarnib in all indications other than virology for a non-refundable $1.0 million upfront license fee and payments upon achievement of certain development and sales-based milestones. Tipifarnib is a clinical stage compound and all ongoing development, regulatory and commercial work will be completed fully and at our sole expense. Under the license agreement, Janssen had a first right to negotiate for an exclusive license back from us to develop and commercialize tipifarnib on terms to be negotiated in good faith. Janssen could exercise this right of first negotiation during a 60-day period following delivery of clinical data as specified in the agreement. In June 2018, Janssen declined to exercise this first right to negotiate.

The agreement will terminate upon the last-to-expire patent rights or last-to-expire royalty term, or may be terminated by us with 180 days written notice of termination. Either party may terminate the agreement in the event of material breach of the agreement that is not cured within 45 days. Janssen may also terminate the agreement due to our lack of diligence that is not cured within a three-month period.

The University of Michigan License Agreement

In December 2014, we entered into a license agreement with the Regents of the University of Michigan, or the University of Michigan, which was amended in March 2015, July 2015, September 2016, February 2017, May 2017 and August 2017, under which we received certain license rights for a non-refundable upfront license, annual maintenance fees and payments upon achievement of certain development and sales-based milestones. The licensed asset consists of several compounds, including our development candidate KO-539. All future development, regulatory and commercial work on the asset will be completed fully and at our sole expense. The University of Michigan retains the right to use the asset for non-commercial research, internal and/or educational purposes, with the right to grant the same limited rights to other non-profit research institutions.

The agreement will terminate upon the last-to-expire patent rights, or may be terminated by us at any time with 90 days written notice of termination or terminated by the University of Michigan upon a bankruptcy by us, payment failure by us that is not cured within 30 days or a material breach of the agreement by us that is not cured within 60 days.

Future Milestone Payments under License Agreements

Collectively, all of our license agreements provide for specified development, regulatory and sales-based milestone payments up to a total of $80.0 million payable upon occurrence of each stated event, of which $0.5 million relates to the initiation of certain development activities, $28.7 million relates to the achievement of specified regulatory approvals for the first indication and up to $50.8 million for the achievement of specified levels of product sales. Additional payments will be due for each subsequent indication if specified regulatory approvals are achieved. As of December 31, 2019, we have paid a milestone payment of $25,000 under the above-mentioned license agreements. Furthermore, if all the programs are successfully commercialized, we will be required to pay tiered royalties on annual net product sales ranging from the low single digits to the low teens, depending on the volume of sales and the respective agreement.

Araxes Asset Purchase Agreement

In December 2014, we entered into an asset purchase agreement with Araxes Pharma LLC, or Araxes, which was amended and restated in February 2015, under which we purchased certain early stage patent rights related to compounds in the field of oncology for a purchase price of $0.5 million payable under a convertible promissory note. All ongoing development, regulatory and commercial work will be completed fully and at our sole expense. The agreement allows for contingent milestone payments of $9.7 million throughout development and commercialization of the asset, of which $1.2 million relates to the initiation of certain development activities, and $8.5 million relates to the submission of certain regulatory filings and receipt of certain regulatory approvals. To date, we have paid to Araxes $0.3 million in milestone payments. Additional payments will be due for each subsequent indication if specified regulatory approvals are achieved. Furthermore, if the program is successfully commercialized, we will be required to pay tiered royalties on annual net product sales ranging in the low single digits, depending on the volume of sales. All milestone payments under the agreement will be recognized upon completion of the required events because the triggering events will not be considered to be probable until they are achieved. For the year ended December 31, 2017, we paid to Araxes a milestone payment of $0.2 million upon the dosing of the first patient in the first KO-947 Phase 1 clinical trial in the second quarter of 2017. There were no milestone payments to Araxes in 2019 or 2018.

Share-Based Compensation - Summary of Stock Option Activities (Detail) - Stock Option $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options Outstanding, Beginning Balance, Number of Shares \| shares	3,186
Granted, Number of Shares \| shares	1,948
Exercised, Number of Shares \| shares	(418)
Canceled, Number of Shares \| shares	(636)
Stock Options Outstanding, Ending Balance, Number of Shares \| shares	4,080
Vested and expected to vest, Number of Shares \| shares	4,080
Exercisable, Number of Shares \| shares	1,882
Outstanding, Beginning Balance, Weighted-Average Exercise Price per Share \| $ / shares	$ 11.93
Granted, Weighted-Average Exercise Price per Share \| $ / shares	16.19
Exercised, Weighted-Average Exercise Price per Share \| $ / shares	6.14
Canceled, Weighted-Average Exercise Price per Share \| $ / shares	15.63
Outstanding, Ending Balance, Weighted-Average Exercise Price per Share \| $ / shares	13.98
Vested and expected to vest, Weighted-Average Exercise Price per Share \| $ / shares	13.98
Exercisable, Weighted-Average Exercise Price per Share \| $ / shares	$ 11.37
Outstanding, Weighted-Average Remaining Contractual Term (years)	8 years
Vested and expected to vest, Weighted-Average Remaining Contractual Term (years)	8 years
Exercisable, Weighted-Average Remaining Contractual Term (years)	7 years
Outstanding, Aggregate Intrinsic Value \| $	$ 9,080
Vested and expected to vest, Aggregate Intrinsic Value \| $	9,080
Exercisable, Aggregate Intrinsic Value \| $	$ 7,663

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Reclassifications

Certain prior period balances have been reclassified to conform to the current period presentation.

Use of Estimates

Our financial statements are prepared in accordance with accounting principles generally accepted in the United States. The preparation of our financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period.

Reported amounts and note disclosures reflect the overall economic conditions that are most likely to occur and anticipated measures management intends to take. Actual results could differ materially from those estimates. All revisions to accounting estimates are recognized in the period in which the estimates are revised and in any future periods affected.

Segment Reporting

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. We operate in a single industry segment which is the discovery and development of precision medicines for the treatment of cancer. Our chief operating decision-maker reviews the operating results on an aggregate basis and manages the operations as a single operating segment in the United States.

Cash and Cash Equivalents

Cash and cash equivalents consist of checking, money market and highly liquid investments that are readily convertible to cash and that have an original maturity of three months or less. The carrying amounts approximate fair value due to the short maturities of these instruments.

Short-Term Investments

Short-term investments are marketable securities with maturities greater than three months from date of purchase that are specifically identified to fund current operations. These investments are classified as current assets, even though the stated maturity date may be one year or more beyond the current balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities to fund our operations, as necessary. The cost of short-term investments is adjusted for amortization of premiums or accretion of discounts to maturity, and such amortization or accretion is included in interest income. Dividend and interest income is recognized as interest income on the statements of operations and comprehensive loss when earned. Short-term investments are classified as available-for-sale securities and carried at fair value with unrealized gains and losses recorded in other comprehensive income (loss) and included as a separate component of stockholders' equity. Realized gains and losses from the sale of available-for-sale securities and declines in value judged to be

other than temporary on short-term investments, if any, are determined on a specific identification basis and are reclassified out of comprehensive loss and included in interest income on the statements of operations and comprehensive loss.

Fair Value Measurements

Fair value is defined as the exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

•

Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities;

•

Level 2 - Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable;

•

Level 3 - Unobservable inputs in which little or no market activity exists, therefore requiring an entity to develop its own assumptions about the assumptions that market participants would use in pricing.

Concentration of Credit Risk

Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash, cash equivalents and short-term investments. We maintain deposits in federally insured financial institutions in excess of federally insured limits. We have established guidelines to limit our exposure to credit risk by placing investments with high credit quality financial institutions, diversifying our investment portfolio and placing investments with maturities that maintain safety and liquidity. We periodically review and modify these guidelines to maximize trends in yields and interest rates without compromising safety and liquidity.

Property and Equipment

Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets. Computer software and equipment are depreciated over their estimated useful lives of three years. Laboratory equipment is depreciated over its estimated useful life of five years.

Impairment of Long-Lived Assets

We review our long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. If such circumstances are determined to exist, an estimate of undiscounted future cash flows produced by the long-lived asset, including its eventual residual value, is compared to the carrying value to determine whether impairment exists. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written-down to their estimated fair values. For the years ended December 31, 2019, 2018 and 2017, there were no impairments of the value of long-lived assets.

Leases

We determine if an arrangement is a lease or contains lease components at inception. Short-term leases with an initial term of 12 months or less are not recorded on the balance sheet. For operating leases with an initial term greater than 12 months, we recognize operating lease right-of-use, or ROU, assets and operating lease liabilities based on the present value of lease payments over the lease term at commencement date. Operating lease ROU assets are comprised of the lease liability plus any lease payments made and excludes lease incentives. Lease terms may include options to extend or terminate when we are reasonably certain that the option will be exercised. For our operating leases, we generally cannot determine the interest rate implicit in the lease, in which case we use our incremental borrowing rate as the discount rate for the lease. We estimate our incremental borrowing rate for our operating leases based on what we would normally pay to borrow on a collateralized basis over a similar term for an amount equal to the lease payments. Operating lease expense is recognized on a straight-line basis over the lease term.

If a lease is modified, the modified contract is evaluated to determine whether it is or contains a lease. If a lease continues to exist, the lease modification is determined to be a separate contract when the modification grants the lessee an additional right of use that is not included in the original lease and the lease payments increase commensurate with the standalone price for the additional ROU. A lease modification that results in a separate contract will be accounted for in the same manner as a new lease. For a modification that is not a separate contract, we reassess the lease classification using the

modified terms and conditions and the facts and circumstances as of the effective date of the modification and recognize the amount of the remeasurement of the lease liability for the modified lease as an adjustment to the corresponding ROU asset.

Research and Development Expenses

Research and development expenses consist of costs associated with our research and development activities including salaries, benefits, share-based compensation and other personnel costs, clinical trial costs, manufacturing costs for non-commercial products, fees paid to external service providers and consultants, facilities costs and supplies, equipment and materials used in clinical and preclinical studies and research and development. All such costs are charged to research and development expense as incurred when these expenditures have no alternative future uses. We are obligated to make upfront payments upon execution of certain research and development agreements. Advance payments, including nonrefundable amounts, for goods or services that will be used or rendered for future research and development activities are deferred. Such amounts are recognized as expense as the related goods are delivered or the related services are performed or such time when we do not expect the goods to be delivered or services to be performed. Payments that we make in connection with in-licensed technology for a particular research and development project that have no alternative future uses, in other research and development projects or otherwise, and therefore no separate economic values are expensed as research and development costs at the time such costs are incurred. As of December 31, 2019, we have no in-licensed technologies that have alternative future uses in research and development projects or otherwise.

Clinical Trial Costs and Accruals

A significant portion of our clinical trial costs relate to contracts with contract research organizations, or CROs. The financial terms of our CRO contracts may result in payment flows that do not match the periods over which materials or services are provided to us under such contracts. Our objective is to reflect the appropriate clinical trial expenses in our financial statements by matching those expenses with the period in which services and efforts are expended. As part of the process of preparing our financial statements, we rely on cost information provided by our CROs, concerning monthly expenses as well as reimbursement for pass through costs. We are also required to estimate certain of our expenses resulting from our obligations under our CRO contracts. Accordingly, our clinical trial accrual is dependent upon the timely and accurate reporting of CROs and other third-party vendors. If the contracted amounts are modified, for instance, as a result of changes in the clinical trial protocol or scope of work to be performed, we modify our accruals accordingly on a prospective basis. Revisions in the scope of a contract are charged to expense in the period in which the facts that give rise to the revision become reasonably certain. Historically, we have had no material changes in clinical trial expense that had a material impact on our results of operations or financial position.

Patent Costs

We expense all costs as incurred in connection with patent applications, including direct application fees, and the legal and consulting expenses related to making such applications, and such costs are included in general and administrative expenses on the statements of operations and comprehensive loss.

Share-Based Payments

Our share-based awards are measured at fair value on the date of grant based upon the estimated fair value of common stock. The fair value of awards expected to vest are recognized and amortized on a straight-line basis over the requisite service period of the award less actual forfeitures. The fair value of each stock option is estimated on the date of grant using the Black-Scholes option pricing model, or Black-Scholes model, that requires the use of subjective assumptions including volatility, expected term, risk-free rate and the fair value of the underlying common stock.

Subsequent to the adoption of Accounting Standards Update, or ASU, 2018-07 on January 1, 2019, we measured awards granted to non-employees on the adoption date of the standard and recognized the expense over the remaining vesting period of the award. Prior to the adoption of ASU 2018-07, awards granted to non-employees were subject to periodic revaluation over their vesting terms. The fair value of non-employee awards was remeasured at each reporting period as the underlying awards vest unless the instruments were fully vested, immediately exercisable and nonforfeitable on the date of grant. We recorded the expense for stock option grants to non-employees based on the estimated fair value of the stock options using the Black-Scholes model. Estimated fair value of the restricted stock awards granted to non-employees was recorded on the earlier of the performance commitment date or the date the services required were completed and were remeasured at fair value during the service period. As non-employee restricted stock awards vest, they were remeasured at

fair value and expensed based on the intrinsic value method which was measured as the difference between the exercise price paid for the restricted stock award and the fair value of the shares as the right of the repurchase lapses each vesting period.

Income Taxes

Income taxes are accounted for using the asset and liability method. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applicable 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. A valuation allowance against deferred tax assets is recorded if, based upon the weight of all available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. For uncertain tax positions that meet “a more likely than not” threshold, we recognize the benefit of uncertain tax positions in the financial statements.

Comprehensive Loss

Comprehensive loss is defined as the change in equity during the period from transactions and other events and non-owner sources. For the periods presented, accumulated other comprehensive income (loss) consists of unrealized gains and losses on marketable securities and foreign currency.

Net Loss per Share

Net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common shares and common stock equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, outstanding stock options, unvested restricted stock awards, an outstanding warrant and employee stock purchase plan rights are excluded from the calculation of diluted net loss per common share for the periods presented as their effect would be anti-dilutive. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the anti-dilutive effect of the securities.

The following table summarizes the number of potentially dilutive securities that were excluded from our calculation of diluted net loss per share, in thousands:

	Years Ended December 31,
	2019		2018		2017
Stock options		4,080		3,186		2,233
Warrant		34		34		34
Employee stock purchase plan rights		6		5		—
Unvested restricted stock awards		—		—		793
Total		4,120		3,225		3,060

Recent Accounting Pronouncements

In February 2016, the Financial Accounting Standards Board, or FASB, issued ASU 2016-02, Leases (Topic 842), which amended prior accounting standards for leases. ASU 2016-02 requires lessees to recognize ROU assets and lease liabilities on the balance sheet and requires expanded disclosures about leasing arrangements. Subsequently, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements. ASU 2018-11 provides entities another option for transition, allowing entities to not apply the new standard in the comparative periods they present in the financial statements in the year of adoption. We adopted the new lease standard on January 1, 2019, using the alternative modified transition method provided by ASU 2018-11 and did not retrospectively apply to prior periods. We elected the “package of practical expedients” permitted under the transition which allows us not to reassess our historical assessment of whether existing contracts are or contain a lease and the classification of existing lease arrangements, and to calculate the present value of the fixed payments without performing an allocation of lease and non-lease components. As a result of the adoption of the new standard, we recognized operating lease ROU assets and operating lease liabilities of $0.6 million on our balance sheet as of January 1, 2019. ROU assets are recorded in other long-term assets on our balance sheets. Current lease liabilities are recorded in accounts payable and accrued expenses on our balance sheets. The adoption of the new lease standard did not have an impact on our accumulated deficit, and did not have a material impact on our results of operations and cash flows. See the “Operating Leases” section of Note 9, Commitments and Contingencies, for further details.

In June 2018, the FASB issued ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting (Topic 718), which expands the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. The new guidance is intended to simplify aspects of share-based compensation issued to nonemployees by aligning the accounting for share-based payment awards issued to employees and nonemployees as it relates to measurement date and impact of performance conditions. This standard was effective for fiscal years beginning after December 15, 2018, and interim periods within those annual periods. We adopted ASU 2018-07 on January 1, 2019. The adoption of ASU 2018-07 did not have a material impact on our financial statements.

In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes. The new guidance is intended to simplify aspects of the accounting for income taxes, including the elimination of certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, among other changes. This standard is effective for fiscal years beginning after December 15, 2020 and interim periods within those annual years. Early adoption is permitted. We elected to early adopt ASU 2019-12 effective January 1, 2019. The adoption of ASU 2019-12 did not have a material impact on our financial statements.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments, which changes the impairment model for most financial assets and certain other instruments. For trade receivables and other instruments, entities will be required to use a new forward-looking expected loss model that generally will result in the earlier recognition of allowances for losses. For available-for-sale debt securities with unrealized losses that are attributable to credit, the losses will be recognized in earnings as allowances. This guidance is effective for annual reporting periods beginning after December 15, 2019, including interim periods within those years, with early adoption permitted only as of annual reporting periods beginning after December 15, 2018. We adopted ASU 2016-13 on January 1, 2020 and do not expect the adoption of the new standard to have a material impact on our financial statements.

Long-Term Debt - Future Minimum Payments under Term Loan Facility (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
2020	$ 669
2021	3,328
2022	3,160
2023	1,849
Total future minimum payments	9,006
Less: interest payments	(1,506)
Principal amount of long-term debt	7,500
Current portion of long-term debt	(250)
Long-term debt, net	$ 7,250	$ 7,500

Subsequent Event

12 Months Ended

Dec. 31, 2019

Subsequent Events [Abstract]

Subsequent Event

16. Subsequent Event

On January 8, 2020, we entered into the San Diego Lease with BRE CA Office Owner LLC for the lease of approximately 13,420 square feet of rentable area of the building located at 12730 High Bluff Drive, San Diego, California 92130. The commencement of the San Diego Lease is expected to be May 1, 2020. The initial term of the San Diego Lease is five years and four months, to expire on August 31, 2025, and we have a one-time option to extend the San Diego Lease for a period of five additional years. The minimum rent payable under the San Diego Lease will be approximately $58,000 per month for the first year, which amount will increase by 3.0% per year over the initial term. Additionally, the lease provides for an allowance of approximately $1.0 million for the reimbursement of allowable tenant improvements expenses. We expect to use the premises as our new principal executive office and for general office use. In addition to base monthly rent, we will be obligated to pay for taxes, insurance and utilities applicable to the leased property.

Commitments and Contingencies - Schedule of Supplemental Balance Sheet Information Related to Operating Leases (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Lessee Lease Description [Line Items]
Operating lease ROU assets	$ 234	$ 600
Total operating lease liabilities	$ 252	$ 600
Weighted-average remaining lease term (in years)	6 months
Weighted-average discount rate	6.50%
Cambridge, MA
Lessee Lease Description [Line Items]
Operating lease ROU assets	$ 155
Current lease liabilities	156
Araxes Pharma LLC
Lessee Lease Description [Line Items]
Operating lease ROU assets, related party	79
Current lease liabilities, related party	$ 96

Share-Based Compensation - Summary of Assumptions Used in Black-Scholes Model (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value per share	$ 10.93	$ 12.95	$ 4.76
Expected volatility, Minimum	73.10%	76.50%	75.40%
Expected volatility, Maximum	77.20%	79.40%	77.70%
Risk free interest rate, Minimum	2.10%	2.10%	1.40%
Risk free interest rate, Maximum	2.80%	2.80%	2.00%
Employee Stock Option \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months	5 years 6 months
Employee Stock Option \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 29 days	6 years 29 days	6 years 29 days
2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value per share	$ 4.44	$ 3.87
Expected volatility, Minimum	43.90%	53.80%
Expected volatility, Maximum	54.20%	54.40%
Expected term (in years)	6 months	6 months
Risk free interest rate, Minimum	1.90%	1.80%
Risk free interest rate, Maximum	2.50%	2.30%
Weighted average exercise price per share	$ 11.01	$ 10.15

Share-Based Compensation - Summary of Share-based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 9,409	$ 8,654	$ 4,545
Research and development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	3,427	4,623	3,048
General and administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	5,982	4,031	1,497
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense		2,722	2,209
Employee		95	132
Nonemployee		2,627	2,077
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	9,265	5,889	2,336
Employee	9,066	5,581	2,190
Nonemployee	199	308	$ 146
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	144	43
Employee	$ 144	$ 43

Commitments and Contingencies - Additional Information (Detail)			1 Months Ended			12 Months Ended
	Mar. 05, 2019 USD ($)	Aug. 01, 2015 USD ($) ft²	Mar. 31, 2019 USD ($)	Dec. 31, 2016 USD ($) ft²	Aug. 31, 2014 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Remaining lease liabilities						$ 300,000
Future minimum payments required under facility leases prior to adoption of ASU 2016-02, for year ending December 31, 2019							$ 500,000
Future minimum payments required under facility leases prior to adoption of ASU 2016-02, for year ending December 31, 2020							300,000
Rent expense						$ 600,000	$ 500,000	$ 400,000
Cambridge, MA
Loss Contingencies [Line Items]
Operating lease, area of space \| ft²		3,766
Security deposit		$ 44,000
Lease term period		60 months
Lease expiration date		Aug. 01, 2020
Office space lease monthly rent		$ 21,000
Operating lease rate of increase in annual rent		1.40%
Total base rent payable over the lease period		$ 1,300,000
Araxes Pharma LLC \| San Diego Sublease
Loss Contingencies [Line Items]
Percentage of rent escalation				3.00%	3.00%
Sublease expiration date				Oct. 31, 2019	Oct. 31, 2019
Sublease expiration period					2017-06
Operating lease, area of space \| ft²				5,216
Security deposit				$ 16,000
Sublease term description				The terms of the New Sublease commenced in June 2017
Sublease extended expiration date	Apr. 30, 2020
Increase in sublease liability			$ 100,000
Increase in operating lease ROU asset			$ 100,000
Araxes Pharma LLC \| San Diego Sublease \| Monthly
Loss Contingencies [Line Items]
Rent expense	$ 24,000			$ 16,000	$ 4,820

Income Taxes - Schedule of Activity Related to Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Gross unrecognized tax benefits at the beginning of the year	$ 1,063	$ 615	$ 358
Increases related to prior year tax positions			42
Increases from tax positions taken in the current year	678	448	215
Gross unrecognized tax benefits at the end of the year	$ 1,741	$ 1,063	$ 615

Share-Based Compensation

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-Based Compensation

11. Share-Based Compensation

Equity Incentive Plan

In March 2015, our board of directors adopted our Amended and Restated 2014 Equity Incentive Plan, or 2014 Plan, which provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock unit awards, performance-based stock awards and other forms of equity compensation to our employees and other service providers. The number of shares of our common stock available for future grant under the 2014 Plan will automatically increase on January 1 of each year through January 1, 2025 by 4% of the total number of shares of our common stock outstanding on December 31 of the preceding calendar year, subject to the ability of our board of directors to take action to reduce the size of the increase in any given year. On January 1, 2020, an automatic increase pursuant to the 2014 Plan occurred, resulting in 1,815,361 additional shares available for future grant under the 2014 Plan. We issue shares of common stock upon the exercise of options with the source of those shares of common stock being newly issued shares.

As of December 31, 2019, a total of up to 10,419,120 shares of common stock have been reserved for issuance under the 2014 Plan. As of December 31, 2019, there were 800,835 shares of common stock reserved for future equity awards issuances under the 2014 Plan.

Stock Options

The exercise price of all stock options granted was equal to no less than the estimated fair market value of such stock on the date of grant. Stock options generally vest over a three to four-year period. The maximum contractual term for all options is ten years. The following is a summary of stock option activity for the year ended December 31, 2019, in thousands (except per share and years data):

	Number of Shares			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2018		3,186		$	11.93
Granted		1,948		$	16.19
Exercised		(418	)	$	6.14
Canceled		(636	)	$	15.63
Outstanding at December 31, 2019		4,080		$	13.98		8.0	$	9,080
Vested and expected to vest at December 31, 2019		4,080		$	13.98		8.0	$	9,080
Exercisable at December 31, 2019		1,882		$	11.37		7.0	$	7,663

The aggregate intrinsic value in the above table is calculated as the difference between the closing price of our common stock at December 31, 2019 of $13.75 per share and the exercise price of stock options that had strike prices below the closing price.

The following summarizes certain information regarding stock options, in thousands:

	Years Ended December 31,
	2019		2018		2017
Cash received from options exercised during the period	$	2,562	$	1,035	$	232
Intrinsic value of options exercised during the period	$	4,311	$	1,822	$	151

The assumptions used to estimate the fair value of stock options granted to employees using the Black-Scholes model were as follows:

	Years Ended December 31,
	2019		2018		2017
Weighted average grant date fair value per share	$	10.93	$	12.95	$	4.76
Expected volatility	73.1% — 77.2%		76.5% — 79.4%		75.4% — 77.7%
Expected term (in years)	5.50 — 6.08		5.50 — 6.08		5.50 — 6.08
Risk free interest rate	2.1% — 2.8%		2.1% — 2.8%		1.4% — 2.0%
Expected dividend yield		—		—		—

In estimating fair value for stock options issued under the 2014 Plan, expected volatility was based, in part, on our historical volatility and the historical volatility of comparable publicly-traded companies because our common stock has only been publicly traded since September 16, 2015. Due to the lack of historical option exercise data, we estimated the expected term using the simplified method. The risk-free interest rates are based on the U.S. Treasury zero-coupon bonds with maturities similar to those of the expected term of the award being valued. The expected dividend yield of zero reflects that we have not paid cash dividends since inception and do not intend to pay cash dividends in the foreseeable future. Actual forfeitures are applied as they occur, and any compensation cost previously recognized for awards for which the requisite service has not been completed is reversed in the period that the award is forfeited.

As of December 31, 2019, unrecognized estimated compensation expense related to options was $23.0 million, which is expected to be recognized over the weighted-average remaining requisite service period of approximately 2.7 years.

Restricted Stock Awards

Restricted stock awards were granted at a price equal to the estimated fair market value on the date of grant. The restricted stock awards generally vested over four years from the original vesting date, with certain grants subject to one-year cliff vesting. The vesting provisions of individual awards may vary as approved by our board of directors. In connection with the issuance of restricted common stock, we maintained a repurchase right where shares of restricted common stock were released from such repurchase right over a period of time of continued service by the recipient. The repurchase price for unvested stock awards was the lower of (i) the fair market value of the shares of common stock on the date of repurchase or (ii) their original purchase price. As of December 31, 2019, there were no shares subject to repurchase.

The total fair value of restricted stock awards vested during the years ended December 31, 2018 and 2017 was $14.8 million and $12.7 million, respectively. All restricted stock awards fully vested in 2018.

Employee Stock Purchase Plan

In March 2015, our board of directors adopted the 2015 Employee Stock Purchase Plan, or ESPP. The ESPP permits eligible employees to purchase our common stock at a discount through payroll deductions during defined offering periods. Eligible employees may elect to withhold up to 15% of their base earnings to purchase shares of our common stock at a price equal to 85% of the fair market value on the first day of the offering period or the purchase date, whichever is lower. Successive six-month offering periods under the ESPP began on May 21, 2018. The number of shares of our common stock reserved for issuance under the ESPP will automatically increase on January 1 of each calendar year through January 1, 2025 by the lesser of 1% of the total number of shares of our common stock outstanding on December 31 of the preceding calendar year and 2,000,000 shares, subject to the ability of our board of directors to take action to reduce the size of the increase in any given year. In December 2019, our board of directors elected not to increase the total number of shares of our common stock reserved for issuance under the ESPP for 2020.

For the years ended December 31, 2019 and 2018, cash received from the exercise of purchase rights was approximately $0.4 million and $0.1 million, respectively. As of December 31, 2019, we have issued 39,543 shares under the ESPP. As of December 31, 2019, 199,162 shares of common stock are reserved for future issuance under the ESPP.

The assumptions used to estimate the fair value of ESPP stock purchase rights using the Black-Scholes model were as follows:

	Years Ended December 31,
	2019		2018
Weighted average grant date fair value per share	$	4.44	$	3.87
Weighted average exercise price per share	$	11.01	$	10.15
Expected volatility	43.9% — 54.2%		53.8% — 54.4%
Expected term (in years)		0.50		0.50
Risk free interest rate	1.9% — 2.5%		1.8% — 2.3%
Expected dividend yield		—		—

In estimating fair value for ESPP purchase rights issued, expected volatility was based on our historical volatility. The expected term is six months, which represents the length of each purchase period. The risk-free interest rates are based on the U.S. Treasury zero-coupon bonds with maturities similar to those of the expected term. The expected dividend yield of zero reflects that we have not paid cash dividends since inception and do not intend to pay cash dividends in the foreseeable future.

The following table summarizes share-based compensation expense for all share-based compensation arrangements, in thousands:

	Years Ended December 31,
	2019		2018		2017
Research and development	$	3,427	$	4,623	$	3,048
General and administrative		5,982		4,031		1,497
Total share-based compensation expense	$	9,409	$	8,654	$	4,545

Restricted stock awards:
Employee	$	—	$	95	$	132
Nonemployee		—		2,627		2,077
Total	$	—	$	2,722	$	2,209

Stock options:
Employee	$	9,066	$	5,581	$	2,190
Nonemployee		199		308		146
Total	$	9,265	$	5,889	$	2,336

Employee stock purchase plan:
Employee	$	144	$	43	$	—
Total	$	144	$	43	$	—

Commitments and Contingencies - Schedule of Operating Lease Expense (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Lessee Lease Description [Line Items]
Operating lease costs	$ 503
Cambridge, MA
Lessee Lease Description [Line Items]
Operating lease costs	271
Araxes Pharma LLC
Lessee Lease Description [Line Items]
Operating lease costs	$ 232

Balance Sheet Detail

12 Months Ended

Dec. 31, 2019

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Detail

6. Balance Sheet Detail

Property and equipment consisted of the following, in thousands:

	December 31,
	2019			2018
Computer software and equipment and laboratory equipment	$	136		$	92
Less: accumulated depreciation		(92	)		(92	)
Property and equipment, net	$	44		$	—

There was no depreciation expense for the year ended December 31, 2019. Depreciation expense was $10,000 and $30,000 for the years ended December 31, 2018 and 2017, respectively.

Accounts payable and accrued liabilities consisted of the following, in thousands:

	December 31,
	2019		2018
Accounts payable	$	3,526	$	3,935
Accrued research and development expenses		6,970		5,729
Accrued compensation and benefits		3,694		3,437
Other accrued expenses		1,124		514
Total accounts payable and accrued expenses	$	15,314	$	13,615

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

14. Income Taxes

For the years ended December 31, 2019, 2018 and 2017, we did not record a provision for income taxes due to a full valuation against our deferred taxes.

Our effective income tax rate differs from the statutory federal rate of 21% for the years ended December 31, 2019 and 2018 and 34% for the year ended December 31, 2017, due to the following, in thousands:

	Years Ended December 31,
	2019			2018			2017
Income taxes at statutory federal rate	$	(13,259	)	$	(12,694	)	$	(12,048	)
State income tax, net of federal benefit		(4,810	)		(4,447	)		(2,226	)
Research and development tax credits		(1,664	)		(1,469	)		(476	)
Share-based compensation		708			870			1,046
Other		199			(8	)		(209	)
Tax Cut and Jobs Act		—			—			9,517
Valuation allowance		18,826			17,748			4,396
Income tax expense	$	—		$	—		$	—

Significant components of our deferred tax assets are shown below, in thousands:

	December 31,
	2019			2018
Deferred tax assets
Net operating loss carryforwards	$	53,590		$	37,329
Research and development tax credit carryforwards		4,748			3,140
Share-based compensation		2,134			1,426
Accruals		1,353			931
Intangibles		594			642
Other		171			131
Total deferred tax assets		62,590			43,599
Deferred tax liabilities		(165	)		—
Less valuation allowance		(62,425	)		(43,599	)
Net deferred tax assets	$	—		$	—

As of December 31, 2019, we had federal net operating loss, or NOL, carryforwards of $184.3 million, of which $108.9 million can be carried forward indefinitely. The remaining federal net operating loss carryforwards of $75.4 million will begin to expire in 2034, unless previously utilized. We had state loss carryforwards of $216.7 million, of which $216.2 million begin to expire in 2034 and $0.5 million begin to expire in 2030, unless previously utilized. We also have federal and state research and development credit carryforwards of $4.6 million and $2.2 million, respectively. The federal research and development credits will begin to expire in 2034, unless previously utilized. Of the state research and development credits, $1.5 million will carryforward indefinitely and approximately $0.7 million will begin to expire in 2031, unless previously utilized.

We file tax returns as prescribed by the tax laws of the jurisdictions in which we operate. Our tax years since inception are subject to examination by the federal and state jurisdictions due to the carryforward of unutilized net operating losses and research and development credits. We have not been, nor are we currently, under examination by the federal or any state tax authority.

Management assesses the available positive and negative evidence to estimate if sufficient future taxable income will be generated to use existing deferred tax assets. Based on the weight of the evidence, including our limited existence and losses since inception, management has determined that it is more likely than not that the deferred tax assets will not be realized and therefore has recorded a full valuation allowance against the deferred taxes. The valuation allowance increased by $18.8 million from December 31, 2018.

Pursuant to Sections 382 and 383 of the IRC annual use of our NOL or research and development credit carryforwards may be limited in the event a cumulative change in ownership of more than 50% occurs within a three-year period. We previously completed a study to assess whether an ownership change, as defined by IRC Section 382, had occurred from our formation through March 31, 2016. Based upon this study, we determined that an ownership change occurred but concluded the annual utilization limitation would be sufficient to utilize our pre-ownership change NOLs and research and development credits prior to expiration. We completed additional studies and concluded no further ownership changes occurred through December 31, 2018. We have not completed a study for 2019, however, we do not expect any material limitations to the utilization of NOL’s or research and development credits. Future ownership changes may limit our ability to utilize remaining tax attributes. Any carryforwards that will expire prior to utilization as a result of such additional limitations will be removed from deferred tax assets, with a corresponding reduction of the valuation allowance.

In accordance with authoritative guidance, the impact of an uncertain income tax position is recognized at the largest amount that is “more likely than not” to be sustained upon audit by the relevant taxing authority. An uncertain tax position will not be recognized if it has less than a 50% likelihood of being sustained.

The following table summarizes the activity related to our unrecognized tax benefits, in thousands:

	December 31,
	2019		2018		2017
Gross unrecognized tax benefits at the beginning of the year	$	1,063	$	615	$	358
Increases related to prior year tax positions		—		—		42
Increases from tax positions taken in the current year		678		448		215
Gross unrecognized tax benefits at the end of the year	$	1,741	$	1,063	$	615

Our practice is to recognize interest and penalties related to income tax matters in income tax expense. There was no accrued interest or penalties included on the balance sheets as of December 31, 2019 and 2018, and we have not recognized interest and penalties on the statements of operations and comprehensive loss for the years ended December 31, 2019, 2018 or 2017.

We do not expect that there will be a significant change in the unrecognized tax benefits over the next 12 months. Due to the existence of the valuation allowance, future changes in our unrecognized tax benefits will not impact our effective tax rate.

Long-Term Debt

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Long-Term Debt

7. Long-Term Debt

In April 2016, we entered into a loan and security agreement with Oxford Finance LLC, or Oxford, and Silicon Valley Bank, or SVB, which was amended in May 2017 and October 2017, pursuant to which we borrowed $7.5 million, or SVB-Oxford Term Loan. As discussed below, we extinguished the SVB-Oxford Term Loan in November 2018. In connection with the SVB-Oxford Term Loan, we issued warrants to purchase shares of our common stock. As of December 31, 2019, the warrant issued to Oxford to purchase up to 33,988 shares of our common stock at an exercise price of $3.31 per share remains outstanding.

On November 1, 2018, we entered into a loan and security agreement, or the SVB Loan Agreement, with SVB, or the Lender, providing for up to $20.0 million in a series of term loans. Upon entering into the SVB Loan Agreement, we borrowed $7.5 million, or Term A Loan. We used approximately $6.9 million of the proceeds from the Term A Loan to repay all amounts owed under the SVB-Oxford Loan Agreement, which included a prepayment charge of $0.1 million. The SVB Loan Agreement has substantially different terms than the SVB-Oxford Loan Agreement. In accordance with ASC 405, Extinguishment of Liabilities and ASC 470-50, Debt Modifications and Extinguishments, we accounted for the transaction as a debt extinguishment. Accordingly, we recorded a loss of approximately $0.5 million for the year ended December 31, 2018.

Under the terms of the SVB Loan Agreement, we may, at our sole discretion, borrow from the Lender up to an additional $12.5 million at any time until May 1, 2020, or Term B Loan, and together with Term A Loan, the Term Loans. In addition, each Term B Loan must be in an amount equal to the lesser of $5.0 million or the amount that is remaining under the Term B Loan.

All of the Term Loans will be due on the scheduled maturity date of May 1, 2023, or Maturity Date. Repayment of the Term Loans will be interest only through November 30, 2020, followed by 30 equal monthly payments of principal plus accrued interest commencing on December 1, 2020. The per annum interest rate for any outstanding Term Loans is the greater of (i) 5.50% and (ii) the sum of (a) the prime rate reported in The Wall Street Journal plus (b) 0.25%. The interest rate as of December 31, 2019 was 5.50%. In addition, a final payment of 7.75% of the amounts of the Term Loans drawn will be due on the earlier of the Maturity Date, acceleration of any Term Loans, or prepayment of the Term Loans. The final payment is being accrued through interest expense using the effective interest method. If we elect to prepay the Term Loans, a prepayment fee equal to 1% or 2% of the then outstanding principal balance will also be due, depending upon when the prepayment occurs.

We are subject to customary affirmative and restrictive covenants under the term loan facility. Our obligations under the SVB Loan Agreement are secured by a first priority security interest in substantially all of our current and future assets,

other than our intellectual property. We have also agreed not to encumber our intellectual property assets, except as permitted by the SVB Loan Agreement.

The SVB Loan Agreement also contains customary indemnification obligations and customary events of default, including, among other things, our failure to fulfill certain obligations under the SVB Loan Agreement and the occurrence of a material adverse change in our business, operations, or condition (financial or otherwise), a material impairment of the prospect of repayment of any portion of the loan, or a material impairment in the perfection or priority of Lender’s lien in the collateral or in the value of such collateral. In the event of default by us under the SVB Loan Agreement, the Lender would be entitled to exercise their remedies thereunder, including the right to accelerate the debt, upon which we may be required to repay all amounts then outstanding under the SVB Loan Agreement. The conditional exercisable call option related to the event of default is considered to be an embedded derivative which is required to be bifurcated and accounted for as a separate financial instrument. In the periods presented, the value of the embedded derivative is not material, but could become material in future periods if an event of default became more probable than is currently estimated. As of December 31, 2019 and 2018, we were in compliance with all financial covenants under the SVB Loan Agreement and there had been no material adverse change.

The following table summarizes future minimum payments under the term loan facility as of December 31, 2019, in thousands:

Year Ending December 31,
2020	$	669
2021		3,328
2022		3,160
2023		1,849
Total future minimum payments		9,006
Less: interest payments		(1,506	)
Principal amount of long-term debt		7,500
Current portion of long-term debt		(250	)
Long-term debt, net	$	7,250

Share-Based Compensation - Summary of Information Regarding Stock Options (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Cash received from options exercised during the period	$ 2,562	$ 1,035	$ 232
Intrinsic value of options exercised during the period	$ 4,311	$ 1,822	$ 151

Fair Value Measurements - Schedule Of Fair Value Measurements, By Major Security Type (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 210,756	$ 162,866
Fair Value Measurements on Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	210,756	162,866
Cash equivalents and short-term investments	229,201	171,374
Fair Value Measurements on Recurring Basis \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	76,257	39,723
Cash equivalents and short-term investments	94,702	48,231
Fair Value Measurements on Recurring Basis \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	134,499	123,143
Cash equivalents and short-term investments	134,499	123,143
Fair Value Measurements on Recurring Basis \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	18,445	8,508
Fair Value Measurements on Recurring Basis \| Money Market Funds \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	18,445	8,508
Fair Value Measurements on Recurring Basis \| Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	113,648	56,708
Fair Value Measurements on Recurring Basis \| Corporate Debt Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	113,648	56,708
Fair Value Measurements on Recurring Basis \| U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	76,257	39,723
Fair Value Measurements on Recurring Basis \| U.S. Treasury Securities \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	76,257	39,723
Fair Value Measurements on Recurring Basis \| Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	20,851	66,435
Fair Value Measurements on Recurring Basis \| Commercial Paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 20,851	$ 66,435

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments \| Segment	1
Impairment losses on long-lived assets \| $	$ 0	$ 0	$ 0
Operating lease, existence of option to extend	true
Operating lease, existence of option to extend description	Lease terms may include options to extend or terminate when we are reasonably certain that the option will be exercised.
Operating lease, existence of option to terminate	true
Operating lease, option to terminate description	Lease terms may include options to extend or terminate when we are reasonably certain that the option will be exercised.
Computer Software and Equipment
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	3 years
Laboratory Equipment
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	5 years

Balance Sheet Detail - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Depreciation expense	$ 0	$ 10	$ 30

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Feb. 20, 2020	Jun. 28, 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	KURA
Entity Registrant Name	KURA ONCOLOGY, INC.
Entity Central Index Key	0001422143
Entity Current Reporting Status	Yes
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Public Float			$ 822.0
Entity Common Stock, Shares Outstanding		45,428,045
Entity File Number	001-37620
Entity Tax Identification Number	61-1547851
Entity Address, Address Line One	3033 Science Park Road
Entity Address, Address Line Two	Suite 220
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	500-8800
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false

Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activities

	Number of Shares			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2018		3,186		$	11.93
Granted		1,948		$	16.19
Exercised		(418	)	$	6.14
Canceled		(636	)	$	15.63
Outstanding at December 31, 2019		4,080		$	13.98		8.0	$	9,080
Vested and expected to vest at December 31, 2019		4,080		$	13.98		8.0	$	9,080
Exercisable at December 31, 2019		1,882		$	11.37		7.0	$	7,663

Summary of Information Regarding Stock Options

The following summarizes certain information regarding stock options, in thousands:

	Years Ended December 31,
	2019		2018		2017
Cash received from options exercised during the period	$	2,562	$	1,035	$	232
Intrinsic value of options exercised during the period	$	4,311	$	1,822	$	151

Summary of Assumptions Used in Black-Scholes Model

The assumptions used to estimate the fair value of stock options granted to employees using the Black-Scholes model were as follows:

	Years Ended December 31,
	2019		2018		2017
Weighted average grant date fair value per share	$	10.93	$	12.95	$	4.76
Expected volatility	73.1% — 77.2%		76.5% — 79.4%		75.4% — 77.7%
Expected term (in years)	5.50 — 6.08		5.50 — 6.08		5.50 — 6.08
Risk free interest rate	2.1% — 2.8%		2.1% — 2.8%		1.4% — 2.0%
Expected dividend yield		—		—		—

Summary of Assumptions Used in Black-Scholes Model

The assumptions used to estimate the fair value of ESPP stock purchase rights using the Black-Scholes model were as follows:

	Years Ended December 31,
	2019		2018
Weighted average grant date fair value per share	$	4.44	$	3.87
Weighted average exercise price per share	$	11.01	$	10.15
Expected volatility	43.9% — 54.2%		53.8% — 54.4%
Expected term (in years)		0.50		0.50
Risk free interest rate	1.9% — 2.5%		1.8% — 2.3%
Expected dividend yield		—		—

Summary of Share-based Compensation Expense

The following table summarizes share-based compensation expense for all share-based compensation arrangements, in thousands:

	Years Ended December 31,
	2019		2018		2017
Research and development	$	3,427	$	4,623	$	3,048
General and administrative		5,982		4,031		1,497
Total share-based compensation expense	$	9,409	$	8,654	$	4,545

Restricted stock awards:
Employee	$	—	$	95	$	132
Nonemployee		—		2,627		2,077
Total	$	—	$	2,722	$	2,209

Stock options:
Employee	$	9,066	$	5,581	$	2,190
Nonemployee		199		308		146
Total	$	9,265	$	5,889	$	2,336

Employee stock purchase plan:
Employee	$	144	$	43	$	—
Total	$	144	$	43	$	—

Employee Benefit Plan

12 Months Ended

Dec. 31, 2019

Postemployment Benefits [Abstract]

Employee Benefit Plan

13. Employee Benefit Plan

We have a defined contribution 401(k) plan for all employees. Under the terms of the plan, employees may make voluntary contributions as a percentage or defined amount of compensation. We provide a safe harbor contribution of 3.0% of the employee’s compensation, not to exceed eligible limits. For the years ended December 31, 2019, 2018 and 2017, we incurred approximately $0.3 million, $0.2 million and $0.2 million, respectively, in expenses related to the safe harbor contribution.

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	45,384,000	38,148,000
Common stock, shares outstanding	45,384,000	38,148,000

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
Operating Activities
Net loss	$ (63,140)	$ (60,447)	$ (35,434)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	9,409	8,654	4,545
Non-cash interest expense		184	118
Loss on debt extinguishment		498
Depreciation expense	0	10	30
Amortization of premium and accretion of discounts on marketable securities, net	(1,103)	(1,935)	(260)
Changes in operating assets and liabilities:
Accounts receivable, related party	210	(8)	79
Prepaid expenses and other current assets	(1,085)	(457)	(196)
Other long-term assets	(117)	(504)	(593)
Accounts payable and accrued expenses	856	5,116	3,052
Other long-term liabilities	210	234	218
Net cash used in operating activities	(54,760)	(48,655)	(28,441)
Investing Activities
Purchases of marketable securities	(227,571)	(237,443)	(100,635)
Maturities and sales of marketable securities	181,246	158,143	77,217
Net cash used in investing activities	(46,325)	(79,300)	(23,418)
Financing Activities
Proceeds from issuances of common stock, net	108,165	132,172	53,679
Proceeds from exercise of stock options and purchases under employee stock purchase plan	2,936	1,092	232
Proceeds from issuance of long-term debt, net		627
Repayment of long-term debt		(1,250)
Payment of fee related to long-term debt			(344)
Net cash provided by financing activities	111,101	132,641	53,567
Net increase in cash and cash equivalents	10,016	4,686	1,708
Cash and cash equivalents at beginning of period	16,119	11,433	9,725
Cash and cash equivalents at end of period	26,135	16,119	11,433
Supplemental disclosure of cash flow information:
Interest paid	$ 430	$ 641	$ 627

Investments - Additional Information (Detail) - USD ($)	12 Months Ended
Investments - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Short-term investments with maturities less than one year	$ 196,100,000
Short-term investments with maturities between one to two years	14,700,000
Available-for-sale securities, realized gains or losses		$ 0	$ 0
Marketable securities gross unrealized loss positions for less than twelve months	$ 0	$ 93,500,000
Available for sale securities, debt maturities period		2019-01
Short-term investments maturities, description	As of December 31, 2019, $196.1 million of our short-term investments had maturities less than one year and $14.7 million of our short-term investments had maturities between one to two years. As of December 31, 2018, all of our short-term investments had maturities less than one year.
Unrealized losses other-than-temporary		$ 0
U.S. Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, twelve months or longer, fair value		$ 5,000,000.0

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Number of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share

The following table summarizes the number of potentially dilutive securities that were excluded from our calculation of diluted net loss per share, in thousands:

	Years Ended December 31,
	2019		2018		2017
Stock options		4,080		3,186		2,233
Warrant		34		34		34
Employee stock purchase plan rights		6		5		—
Unvested restricted stock awards		—		—		793
Total		4,120		3,225		3,060

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Selected Quarterly Financial Information [Abstract]

Summary of Quarterly Results

The following is a summary of our quarterly results for the years ended December 31, 2019 and 2018, in thousands, (except per share data):

	Quarter												Year Ended
	First			Second			Third			Fourth			December 31, 2019
Operating expenses	$	14,951		$	15,891		$	17,674		$	18,963		$	67,479
Net loss	$	(13,940	)	$	(14,943	)	$	(16,392	)	$	(17,865	)	$	(63,140	)
Basic and diluted net loss per share	$	(0.37	)	$	(0.38	)	$	(0.36	)	$	(0.39	)	$	(1.51	)
Shared used in computing net loss per share, basic and diluted		38,168			38,928			45,241			45,333			41,946


	Quarter												Year Ended
	First			Second			Third			Fourth			December 31, 2018
Operating expenses	$	14,991		$	15,276		$	15,982		$	16,634		$	62,883
Net loss	$	(14,604	)	$	(14,739	)	$	(15,007	)	$	(16,097	)	$	(60,447	)
Basic and diluted net loss per share	$	(0.46	)	$	(0.45	)	$	(0.40	)	$	(0.42	)	$	(1.72	)
Shared used in computing net loss per share, basic and diluted		31,829			32,971			37,789			38,079			35,191

Stockholders' Equity

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Stockholders' Equity

10. Stockholders’ Equity

In June 2019, we completed a public offering in which we sold an aggregate of 6,785,000 shares of common stock at a price of $17.00 per share. Net proceeds from the public offering, after deducting underwriting discounts, commissions and offering expenses, were approximately $108.1 million.

In March 2019, we entered into an at-the-market issuance sales agreement with SVB Leerink LLC and Stifel, Nicolaus & Company, Incorporated, or the 2019 ATM facility, under which we may offer and sell, from time to time, at our sole discretion, shares of our common stock having an aggregate offering price of up to $75.0 million. We have not yet sold any shares of our common stock under the 2019 ATM facility.

In July 2018, we completed a public offering in which we sold an aggregate of 4,600,000 shares of common stock at a price of $16.75 per share. Net proceeds from the public offering, after deducting underwriting discounts, commissions and offering expenses, were approximately $74.5 million.

In January 2018, we sold an aggregate of 3,136,722 shares of our common stock at a weighted-average price per share of $18.85, for net proceeds of approximately $57.4 million, after deducting commissions and offering expenses, under an at-the-market issuance sales agreement, with Cowen and Company, LLC, which was amended in November 2017 and March 2018, or 2017 ATM facility. In July 2018, we terminated the 2017 ATM facility.

In August 2017, we completed a public offering in which we sold an aggregate of 8,805,000 shares of common stock at a price of $6.50 per share. Net proceeds from the public offering, after deducting underwriting discounts, commissions and offering expenses, were approximately $53.5 million.

Investments (Tables)

12 Months Ended

Dec. 31, 2019

Investments All Other Investments [Abstract]

Investments Measured at Fair Value on Recurring Basis

The following tables summarize, by major security type, our investments that are measured at fair value on a recurring basis, in thousands:

		December 31, 2019
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Cash equivalents:
Money market funds	1 or less	$	18,445	$	—	$	—	$	18,445

Short-term investments:
Corporate debt securities	2 or less		113,466		182		—		113,648
U.S. Treasury securities	2 or less		76,108		149		—		76,257
Commercial paper	1 or less		20,851		—		—		20,851
Total short-term investments			210,425		331		—		210,756
Total		$	228,870	$	331	$	—	$	229,201

		December 31, 2018
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	1 or less	$	8,508	$	—	$	—		$	8,508

Short-term investments:
Corporate debt securities	1 or less		56,779		6		(77	)		56,708
U.S. Treasury securities	1 or less		39,780		—		(57	)		39,723
Commercial paper	1 or less		66,435		—		—			66,435
Total short-term investments			162,994		6		(134	)		162,866
Total		$	171,502	$	6	$	(134	)	$	171,374

Commitments and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

9. Commitments and Contingencies

Operating Leases

In August 2014, we entered into a sublease agreement, or the Sublease, with Wellspring Biosciences, Inc., or Wellspring, a wholly owned subsidiary of Araxes, for office space located on North Torrey Pines Road in La Jolla, California. The Sublease was amended effective September 1, 2014 to provide for a monthly rent of $4,820 per month. The Sublease included rent escalation of 3.0% per year. In addition to the base monthly rent, we were obligated to pay for operating expenses, taxes, insurance and utilities applicable to the subleased property. Pursuant to the terms of the Sublease, as amended again in June 2016, the Sublease would have expired on October 31, 2019. In December 2016, we entered into a third amendment to Sublease pursuant to which the Sublease expired in June 2017.

In December 2016, we entered into a sublease agreement, or the New Sublease, with Wellspring, which was assigned from Wellspring to Araxes in August 2019, for 5,216 square feet of office space located on Science Park Road in San Diego, California for a monthly rent of approximately $16,000 per month and security deposit of approximately $16,000. The New Sublease includes rent escalation of 3.0% per year. In addition to the base monthly rent, we will be obligated to pay for operating costs, amenities fees and all other costs applicable to the subleased property. The terms of the New Sublease commenced in June 2017 and would have expired on October 31, 2019. In March 2019, the New Sublease was amended to extend until April 30, 2020 with the monthly rent increased to approximately $24,000 per month effective November 1, 2019. See Note 12, Related Party Transactions, for further details of the Sublease and New Sublease.

In August 2015, we entered into a lease agreement for approximately 3,766 square feet of office space located in Cambridge, Massachusetts. We paid a security deposit of approximately $44,000. The lease is subject to a 60 month term expiring on August 1, 2020, with initial monthly rent of approximately $21,000 per month, and subject to a 1.4% annual rent

increase. Total base rent payable over the lease period is $1.3 million. In addition to base monthly rent, we are obligated to pay for taxes, insurance and utilities applicable to the leased property.

We determined the New Sublease in San Diego, California and the lease in Cambridge, Massachusetts that existed before the January 1, 2019 adoption of ASU 2016-02 are operating leases under ASC 842. We determined the March 2019 amendment of the New Sublease did not modify the ROU asset and, therefore, was not a separate contract. Accordingly, we reassessed the lease classification and concluded the operating lease classification remained appropriate. The modified lease terms were included in determining the present value of lease payments for the sublease at the modification date. As such, we recognized an adjustment of approximately $0.1 million as an increase to the sublease liability and ROU asset. We do not have any new operating leases with terms greater than 12 months nor any finance leases as of December 31, 2019.

Operating lease expense was as follows, in thousands:

	Year Ended
	December 31, 2019
Operating lease cost	$	271
Operating lease cost, related party		232
Total operating lease costs	$	503

Supplemental cash flow information related to our operating leases was as follows, in thousands:

	Year Ended
	December 31, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	270
Operating cash flows from operating leases, related party		215
Total cash paid for amounts included in the measurement of lease liabilities	$	485

ROU assets obtained in exchange for operating lease liabilities	$	251
ROU assets obtained in exchange for operating lease liabilities, related party		221
Total ROU assets obtained in exchange for operating lease liabilities	$	472

Supplemental balance sheet information related to our operating leases was as follows, in thousands (except lease term and discount rate):

	December 31, 2019
Operating lease ROU assets	$	155
Operating lease ROU assets, related party		79
Total operating lease ROU assets	$	234

Current lease liabilities	$	156
Current lease liabilities, related party		96
Total operating lease liabilities	$	252

Weighted-average remaining lease term (in years)		0.5
Weighted-average discount rate		6.5	%

As of December 31, 2019, we had remaining lease liabilities of approximately $0.3 million which will mature in 2020. As of December 31, 2018, prior to the adoption of ASU 2016-02, future minimum payments required under the facility leases were $0.5 million and $0.3 million for the years ending December 31, 2019 and 2020, respectively.

Rent expense for the years ended December 31, 2019, 2018 and 2017 was approximately $0.6 million, $0.5 million and $0.4 million, respectively.

In January 2020, we entered into a lease agreement with BRE CA Office Owner LLC for office space in San Diego, California which is expected to commence in May 2020, or the San Diego Lease. See Note 16, Subsequent Event, for further details of the San Diego Lease.

Litigation

From time to time, we may be involved in disputes, including litigation, relating to claims arising out of operations in the normal course of our business. Any of these claims could subject us to costly legal expenses and, while we generally believe that we have adequate insurance to cover many different types of liabilities, our insurance carriers may deny coverage or our policy limits may be inadequate to fully satisfy any damage awards or settlements. If this were to happen, the payment of any such awards could have a material adverse effect on our results of operations and financial position. Additionally, any such claims, whether or not successful, could damage our reputation and business. We currently are not a party to any legal proceedings, the adverse outcome of which, in management’s opinion, individually or in the aggregate, would have a material adverse effect on our results of operations or financial position.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2019

Selected Quarterly Financial Information [Abstract]

Selected Quarterly Financial Data (Unaudited)

15. Selected Quarterly Financial Data (Unaudited)

The following is a summary of our quarterly results for the years ended December 31, 2019 and 2018, in thousands, (except per share data):

	Quarter												Year Ended
	First			Second			Third			Fourth			December 31, 2019
Operating expenses	$	14,951		$	15,891		$	17,674		$	18,963		$	67,479
Net loss	$	(13,940	)	$	(14,943	)	$	(16,392	)	$	(17,865	)	$	(63,140	)
Basic and diluted net loss per share	$	(0.37	)	$	(0.38	)	$	(0.36	)	$	(0.39	)	$	(1.51	)
Shared used in computing net loss per share, basic and diluted		38,168			38,928			45,241			45,333			41,946


	Quarter												Year Ended
	First			Second			Third			Fourth			December 31, 2018
Operating expenses	$	14,991		$	15,276		$	15,982		$	16,634		$	62,883
Net loss	$	(14,604	)	$	(14,739	)	$	(15,007	)	$	(16,097	)	$	(60,447	)
Basic and diluted net loss per share	$	(0.46	)	$	(0.45	)	$	(0.40	)	$	(0.42	)	$	(1.72	)
Shared used in computing net loss per share, basic and diluted		31,829			32,971			37,789			38,079			35,191

Net loss per share is computed independently for each of the quarters presented. Therefore, the sum of the quarterly per-share calculations will not necessarily equal the annual per share calculation.

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Expenses:
Research and development (includes related party amounts of $432, $1,021 and $1,312 for the years ended December 31, 2019, 2018 and 2017, respectively)	$ 47,826	$ 46,787	$ 26,426
General and administrative (includes related party amounts of $325, $273 and $247 for the years ended December 31, 2019, 2018 and 2017, respectively)	19,653	16,096	9,651
Total operating expenses	67,479	62,883	36,077
Other Income (Expense):
Management fee income, related party	245	735	780
Interest income	4,674	3,169	751
Interest expense	(580)	(970)	(888)
Loss from extinguishment of debt		(498)
Total other income	4,339	2,436	643
Net Loss	$ (63,140)	$ (60,447)	$ (35,434)
Net loss per share, basic and diluted	$ (1.51)	$ (1.72)	$ (1.52)
Weighted average number of shares used in computing net loss per share, basic and diluted	41,946	35,191	23,237
Comprehensive Loss:
Net loss	$ (63,140)	$ (60,447)	$ (35,434)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities and foreign currency	462	(82)	(31)
Comprehensive loss	$ (62,678)	$ (60,529)	$ (35,465)

Employee Benefit Plan - Additional Information (Detail) - Safe Harbor 401(k) Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
Expenses related to contribution plan	$ 300	$ 200	$ 200
Maximum
Defined Contribution Plan Disclosure [Line Items]
Percent of employees compensation	3.00%

Related Party Transactions

12 Months Ended

Dec. 31, 2019

Related Party Transactions

12. Related Party Transactions

Our president and chief executive officer is also the sole managing member of Araxes, and is a significant stockholder of each of us and Araxes. The following is a summary of transactions with Araxes for the years ended December 31, 2019, 2018 and 2017:

•

Asset Purchase Agreement

Under the asset purchase agreement with Araxes, for the year ended December 31, 2017, we paid to Araxes a milestone payment of $0.2 million upon dosing of the first patient in the first KO-947 Phase 1 clinical trial in April 2017. There were no payments to Araxes under the asset purchase agreement for the years ended December 31, 2019 or 2018.

•

Facility Sublease

We sublease office space in San Diego, California from Araxes. Rent expense, including operating costs, related to the Sublease and the New Sublease, as applicable, for each of the years ended December 31, 2019, 2018 and 2017 was approximately $0.4 million, $0.3 million and $0.2 million, respectively. Pursuant to the terms of the Sublease, as amended in June 2016, the Sublease would have expired on October 31, 2019. In December 2016, we entered into a third amendment to Sublease pursuant to which the Sublease expired in June 2017.

In December 2016, we entered into the New Sublease with Wellspring, which was assigned from Wellspring to Araxes in August 2019, for office space in San Diego, California. The New Sublease commenced in June 2017 and would have expired on October 31, 2019. In March 2019, the New Sublease was amended to extend until April 30, 2020, and the monthly rent increased to approximately $24,000 per month effective November 1, 2019. See Note 9, Commitments and Contingencies, for further details of the terms of the Sublease and New Sublease.

•

Management Fees

We have a management services agreement with Araxes pursuant to which Araxes pays us monthly fees for management services calculated based on costs incurred by us in the provision of services to Araxes, plus a reasonable mark-up. For the years ended December 31, 2019, 2018 and 2017, we recorded approximately $0.2 million, $0.7 million and $0.8 million, respectively, of management fee income. In addition, the agreement allows for Araxes to reimburse us an amount equal to the number of full-time equivalents, or FTE, performing research and development services for Araxes, at an annual FTE rate of approximately $374,000, plus actual expenses as reasonably incurred. The initial term of this agreement expired on December 31, 2015 but, pursuant to the terms of the agreement, renews automatically for additional consecutive one-year periods. The agreement may be terminated by either party with a notice of at least 30 days prior to the expiration of the then-renewal term. For the years ended December 31, 2019, 2018 and 2017, we recorded reimbursements of approximately $0.1 million, $0.2 million and $0.3 million, respectively, for research and development services provided to Araxes, which was recorded as a reduction to research and development expenses on the statements of operations and comprehensive loss. As of December 31, 2019 and 2018, approximately nil and $0.2 million, respectively, related to management fees and reimbursements of research and development services are included in accounts receivable, related party on the balance sheets.

•

Services Agreement

We have a services agreement with Wellspring pursuant to which we pay Wellspring for research and development services provided to us in an amount equal to the number of FTE’s performing the services, at an annual FTE rate of $400,000, plus actual expenses as reasonably incurred. The initial term of this services agreement expired on December 31, 2015 but, pursuant to the terms of the agreement, renews automatically for additional consecutive one-year periods. The agreement may be terminated by either party with a notice of at least 30 days prior to the expiration of the then-renewal term. For the years ended December 31, 2019, 2018 and 2017, we recognized approximately $0.2 million, $1.0 million and $1.2 million, respectively, from research and development services provided to us under this agreement as research and development expense on the statements of operations and comprehensive loss. As of December 31, 2019 and 2018, approximately nil and $0.2 million, respectively, related to research and development services under this agreement are included in accounts payable and accrued expenses on the balance sheets.

We have a services agreement with ALG Partners, Inc., or ALG Partners, a recruiting and temporary staffing agency. Our chief operating officer is an immediate family member of the president of ALG Partners. For the year ended December 31, 2019, expenses recognized as related party transactions with ALG Partners were approximately $0.1 million. There were no related party expenses with ALG Partners for the years ended December 31, 2018 and 2017.

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income taxes at statutory federal rate	$ (13,259)	$ (12,694)	$ (12,048)
State income tax, net of federal benefit	(4,810)	(4,447)	(2,226)
Research and development tax credits	(1,664)	(1,469)	(476)
Share-based compensation	708	870	1,046
Other	199	(8)	(209)
Tax Cut and Jobs Act			9,517
Valuation allowance	18,826	17,748	4,396
Income tax expense	$ 0	$ 0	$ 0

Balance Sheet Detail (Tables)

12 Months Ended

Dec. 31, 2019

Balance Sheet Related Disclosures [Abstract]

Summary of Property and Equipment

Property and equipment consisted of the following, in thousands:

	December 31,
	2019			2018
Computer software and equipment and laboratory equipment	$	136		$	92
Less: accumulated depreciation		(92	)		(92	)
Property and equipment, net	$	44		$	—

Summary of Accounts Payable and Accrued Liabilities

Accounts payable and accrued liabilities consisted of the following, in thousands:

	December 31,
	2019		2018
Accounts payable	$	3,526	$	3,935
Accrued research and development expenses		6,970		5,729
Accrued compensation and benefits		3,694		3,437
Other accrued expenses		1,124		514
Total accounts payable and accrued expenses	$	15,314	$	13,615

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

Reclassifications

Certain prior period balances have been reclassified to conform to the current period presentation.

Use of Estimates

Segment Reporting

Cash and Cash Equivalents

Short-Term Investments

Fair Value Measurements

•

Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities;

•

Level 2 - Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable;

•

Concentration of Credit Risk

Property and Equipment

Impairment of Long-Lived Assets

Leases

Research and Development Expenses

Clinical Trial Costs and Accruals

Patent Costs

Share-Based Payments

Income Taxes

Comprehensive Loss

Net Loss per Share

The following table summarizes the number of potentially dilutive securities that were excluded from our calculation of diluted net loss per share, in thousands:

	Years Ended December 31,
	2019		2018		2017
Stock options		4,080		3,186		2,233
Warrant		34		34		34
Employee stock purchase plan rights		6		5		—
Unvested restricted stock awards		—		—		793
Total		4,120		3,225		3,060

Investments

12 Months Ended

Dec. 31, 2019

Investments All Other Investments [Abstract]

Investments

4. Investments

We invest in available-for-sale securities consisting of money market funds, corporate debt securities, U.S. Treasury securities and commercial paper. Available-for-sale securities are classified as part of either cash and cash equivalents or short-term investments on the balance sheets.

The following tables summarize, by major security type, our investments that are measured at fair value on a recurring basis, in thousands:

		December 31, 2019
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Cash equivalents:
Money market funds	1 or less	$	18,445	$	—	$	—	$	18,445

Short-term investments:
Corporate debt securities	2 or less		113,466		182		—		113,648
U.S. Treasury securities	2 or less		76,108		149		—		76,257
Commercial paper	1 or less		20,851		—		—		20,851
Total short-term investments			210,425		331		—		210,756
Total		$	228,870	$	331	$	—	$	229,201

		December 31, 2018
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	1 or less	$	8,508	$	—	$	—		$	8,508

Short-term investments:
Corporate debt securities	1 or less		56,779		6		(77	)		56,708
U.S. Treasury securities	1 or less		39,780		—		(57	)		39,723
Commercial paper	1 or less		66,435		—		—			66,435
Total short-term investments			162,994		6		(134	)		162,866
Total		$	171,502	$	6	$	(134	)	$	171,374

The available-for-sale investments are classified as current assets, even though the stated maturity date may be one year or more beyond the current balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities to fund our operations, as necessary. As of December 31, 2019, $196.1 million of our short-term investments had maturities less than one year and $14.7 million of our short-term investments had maturities between one to two years. As of December 31, 2018, all of our short-term investments had maturities less than one year. Realized gains and losses were de minimus for the year ended December 31, 2019. There were no realized gains or losses for the years ended December 31, 2018 and 2017. As of December 31, 2019, there were no marketable securities in gross unrealized loss positions, compared to $93.5 million of our marketable securities which were in gross unrealized loss positions as of December 31, 2018, of which $5.0 million of U.S. Treasury securities had been in such position for greater than 12 months and subsequently matured in January 2019.

At each reporting date, we perform an evaluation of our marketable securities to determine if any unrealized losses are other-than-temporary. Factors considered in determining whether a loss is other-than-temporary include (i) the financial strength of the issuing institution, (ii) the length of time and extent for which fair value has been less than the cost basis and (iii) our intent and ability to hold our investments in unrealized loss positions until their amortized cost basis has been recovered. Based on our evaluation, we determined that our unrealized losses were not other-than-temporary as of December 31, 2018.

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Provision for income taxes	$ 0	$ 0	$ 0
Effective federal statutory income tax rate, percent	21.00%	21.00%	34.00%
Increase in valuation allowance	$ 18,800,000
Income tax examination, likelihood of unfavorable settlement	An uncertain tax position will not be recognized if it has less than a 50% likelihood of being sustained.
Unrecognized interest or penalties	$ 0	$ 0	$ 0
Domestic Tax Authority
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	$ 184,300,000
Loss carryforwards begin to expire	2034
Research and development credit carryforwards	$ 4,600,000
Credit carry forward begin to expire	2034
Domestic Tax Authority \| Fiscal Year 2019
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	$ 108,900,000
Domestic Tax Authority \| Expire in 2034
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	75,400,000
State and Local Jurisdiction
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	216,700,000
Research and development credit carryforwards	2,200,000
State and Local Jurisdiction \| Research and Development Credits
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Credit carryforwards not subject to expiration	1,500,000
State and Local Jurisdiction \| Expire in 2034
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	$ 216,200,000
Loss carryforwards begin to expire	2034
State and Local Jurisdiction \| Expire in 2030
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	$ 500,000
Loss carryforwards begin to expire	2030
State and Local Jurisdiction \| Expire in 2032 \| Research and Development Credits
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Credit carry forward begin to expire	2031
Credit carryforwards subject to expiration	$ 700,000

License Agreements - Additional Information (Detail) - USD ($)			1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 22, 2014	Dec. 18, 2014	Dec. 31, 2014	Jun. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 23, 2014
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties	$ 80,000,000.0
Milestone paid to date					$ 25,000
Janssen License Agreement
License Agreements [Line Items]
Agreement termination written notice		180 days
Agreement termination notice period in event of material breach		45 days
Janssen License Agreement \| Up front Payment Arrangement
License Agreements [Line Items]
Upfront license fee		$ 1,000,000.0
Initiation of Certain Development Activities
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties	500,000
Specified Regulatory Approvals
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties	28,700,000
Specified Levels of Product Sales
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties	$ 50,800,000
The University of Michigan License Agreement
License Agreements [Line Items]
Agreement termination written notice	90 days
Agreement termination notice period in event of material breach	60 days
License agreement date	Dec. 22, 2014
Agreement termination period due to payment failure	30 days
Araxes Asset Purchase Agreement
License Agreements [Line Items]
Milestone paid to date				$ 200,000	0	$ 0
Convertible notes payable							$ 500,000
Contingent Milestone Payables							$ 9,700,000
Milestone payments paid to date					$ 300,000
Araxes Asset Purchase Agreement \| Certain Regulatory Filings and Approvals
License Agreements [Line Items]
Contingent milestone payments			$ 8,500,000
Araxes Asset Purchase Agreement \| Initiation of Certain Development Activities
License Agreements [Line Items]
Contingent milestone payments			$ 1,200,000

Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Future Minimum Payments under Term Loan Facility

The following table summarizes future minimum payments under the term loan facility as of December 31, 2019, in thousands:

Year Ending December 31,
2020	$	669
2021		3,328
2022		3,160
2023		1,849
Total future minimum payments		9,006
Less: interest payments		(1,506	)
Principal amount of long-term debt		7,500
Current portion of long-term debt		(250	)
Long-term debt, net	$	7,250

Related Party Transactions - Additional Information (Detail) - USD ($)				1 Months Ended	12 Months Ended
	Jun. 01, 2017	Apr. 30, 2016	Oct. 01, 2014	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Rent expense related to office space sublease					$ 600,000	$ 500,000	$ 400,000
Management fee income					245,000	735,000	780,000
Accounts receivable, related party					30,000	224,000
Research and development, related party					432,000	1,021,000	1,312,000
Araxes Pharma LLC
Related Party Transaction [Line Items]
Milestone payment paid					0	0	200,000
San Diego, California \| Araxes Pharma LLC
Related Party Transaction [Line Items]
Sublease expiration date	Oct. 31, 2019
Sublease commencement date	Jun. 30, 2017
Sublease extended expiration date				Apr. 30, 2020
Amended sublease effective date				Nov. 01, 2019
San Diego, California \| Sublease
Related Party Transaction [Line Items]
Rent expense related to office space sublease					$ 400,000	300,000	200,000
San Diego, California \| Monthly \| Araxes Pharma LLC
Related Party Transaction [Line Items]
Rent expense, amended sublease				$ 24,000
La Jolla, California \| Sublease
Related Party Transaction [Line Items]
Sublease agreement description					Pursuant to the terms of the Sublease, as amended in June 2016, the Sublease would have expired on October 31, 2019. In December 2016, we entered into a third amendment to Sublease pursuant to which the Sublease expired in June 2017.
Management Fees \| Araxes Pharma LLC
Related Party Transaction [Line Items]
Research and development services reimbursement, description					In addition, the agreement allows for Araxes to reimburse us an amount equal to the number of full-time equivalents, or FTE, performing research and development services for Araxes, at an annual FTE rate of approximately $374,000, plus actual expenses as reasonably incurred. The initial term of this agreement expired on December 31, 2015 but, pursuant to the terms of the agreement, renews automatically for additional consecutive one-year periods. The agreement may be terminated by either party with a notice of at least 30 days prior to the expiration of the then-renewal term.
Management fee income					$ 200,000	700,000	800,000
Service Agreement for research and development		$ 374,000
Agreement expiration date			Dec. 31, 2015
Agreement termination notice period			30 days
Reimbursements of research and development services for related party					100,000	200,000	300,000
Accounts receivable, related party						200,000
Service Agreements \| Wellspring Biosciences Inc
Related Party Transaction [Line Items]
Agreement expiration date			Dec. 31, 2015
Agreement termination notice period			30 days
Research and development services expense at full time equivalents rate			$ 400,000
Research and development expense payment, description					We have a services agreement with Wellspring pursuant to which we pay Wellspring for research and development services provided to us in an amount equal to the number of FTE’s performing the services, at an annual FTE rate of $400,000, plus actual expenses as reasonably incurred. The initial term of this services agreement expired on December 31, 2015 but, pursuant to the terms of the agreement, renews automatically for additional consecutive one-year periods. The agreement may be terminated by either party with a notice of at least 30 days prior to the expiration of the then-renewal term.
Research and development, related party					$ 200,000	1,000,000.0	1,200,000
Accrued expenses, related party						200,000
Service Agreements \| ALG Partners, LLC
Related Party Transaction [Line Items]
Research and development expense payment, description					We have a services agreement with ALG Partners, Inc., or ALG Partners, a recruiting and temporary staffing agency. Our chief operating officer is an immediate family member of the president of ALG Partners.
Research and development, related party					$ 100,000	$ 0	$ 0

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Schedule Of Fair Value Measurements, By Major Security Type

The following tables summarize, by major security type, our cash equivalents and short-term investments that are measured at fair value on a recurring basis and are categorized using the fair value hierarchy, in thousands:

	December 31, 2019
	Balance		Level 1		Level 2
Cash equivalents:
Money market funds	$	18,445	$	18,445	$	—

Short-term investments:
Corporate debt securities		113,648		—		113,648
U.S. Treasury securities		76,257		76,257		—
Commercial paper		20,851		—		20,851
Total short-term investments		210,756		76,257		134,499
Total	$	229,201	$	94,702	$	134,499

	December 31, 2018
	Balance		Level 1		Level 2
Cash equivalents:
Money market funds	$	8,508	$	8,508	$	—

Short-term investments:
Corporate debt securities		56,708		—		56,708
U.S. Treasury securities		39,723		39,723		—
Commercial paper		66,435		—		66,435
Total short-term investments		162,866		39,723		123,143
Total	$	171,374	$	48,231	$	123,143

STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid- In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2016	$ 56,876	$ 2	$ 110,748	$ (18)	$ (53,856)
Beginning balance (in shares) at Dec. 31, 2016		19,348
Issuance of common stock, net of offering costs	53,674	$ 1	53,673
Issuance of common stock, net of offering costs, (in shares)		8,836
Share-based compensation expense	4,545		4,545
Restricted stock awards vested	3		3
Restricted stock awards vested (in shares)		1,193
Issuance of common stock from exercise of options	232		232
Issuance of common stock from exercise of options (in shares)		47
Other comprehensive income (loss)	(31)			(31)
Net loss	(35,434)				(35,434)
Ending balance at Dec. 31, 2017	79,865	$ 3	169,201	(49)	(89,290)
Ending balance (in shares) at Dec. 31, 2017		29,424
Issuance of common stock, net of offering costs	131,901	$ 1	131,900
Issuance of common stock, net of offering costs, (in shares)		7,737
Share-based compensation expense	8,654		8,654
Restricted stock awards vested	2		2
Restricted stock awards vested (in shares)		793
Issuance of common stock from exercise of options and employee stock purchase plan	1,092		1,092
Issuance of common stock from exercise of options and employee stock purchase plan (in shares)		194
Other comprehensive income (loss)	(82)			(82)
Net loss	(60,447)				(60,447)
Ending balance at Dec. 31, 2018	160,985	$ 4	310,849	(131)	(149,737)
Ending balance (in shares) at Dec. 31, 2018		38,148
Issuance of common stock, net of offering costs	108,129	$ 1	108,128
Issuance of common stock, net of offering costs, (in shares)		6,785
Share-based compensation expense	9,409		9,409
Issuance of common stock from exercise of options and employee stock purchase plan	2,936		2,936
Issuance of common stock from exercise of options and employee stock purchase plan (in shares)		451
Other comprehensive income (loss)	462			462
Net loss	(63,140)				(63,140)
Ending balance at Dec. 31, 2019	$ 218,781	$ 5	$ 431,322	$ 331	$ (212,877)
Ending balance (in shares) at Dec. 31, 2019		45,384

Balance Sheet Detail - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Computer software and equipment and laboratory equipment	$ 136	$ 92
Less: accumulated depreciation	(92)	$ (92)
Property and equipment, net	$ 44

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

	Years Ended December 31,
	2019			2018			2017
Income taxes at statutory federal rate	$	(13,259	)	$	(12,694	)	$	(12,048	)
State income tax, net of federal benefit		(4,810	)		(4,447	)		(2,226	)
Research and development tax credits		(1,664	)		(1,469	)		(476	)
Share-based compensation		708			870			1,046
Other		199			(8	)		(209	)
Tax Cut and Jobs Act		—			—			9,517
Valuation allowance		18,826			17,748			4,396
Income tax expense	$	—		$	—		$	—

Components of Deferred Tax Assets

Significant components of our deferred tax assets are shown below, in thousands:

	December 31,
	2019			2018
Deferred tax assets
Net operating loss carryforwards	$	53,590		$	37,329
Research and development tax credit carryforwards		4,748			3,140
Share-based compensation		2,134			1,426
Accruals		1,353			931
Intangibles		594			642
Other		171			131
Total deferred tax assets		62,590			43,599
Deferred tax liabilities		(165	)		—
Less valuation allowance		(62,425	)		(43,599	)
Net deferred tax assets	$	—		$	—

Schedule of Activity Related to Unrecognized Tax Benefits

The following table summarizes the activity related to our unrecognized tax benefits, in thousands:

	December 31,
	2019		2018		2017
Gross unrecognized tax benefits at the beginning of the year	$	1,063	$	615	$	358
Increases related to prior year tax positions		—		—		42
Increases from tax positions taken in the current year		678		448		215
Gross unrecognized tax benefits at the end of the year	$	1,741	$	1,063	$	615

Balance Sheet Detail - Summary of Accounts Payable and Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accounts payable	$ 3,526	$ 3,935
Accrued research and development expenses	6,970	5,729
Accrued compensation and benefits	3,694	3,437
Other accrued expenses	1,124	514
Total accounts payable and accrued expenses	$ 15,314	$ 13,615

Subsequent Event - Additional Information (Detail)		12 Months Ended
Subsequent Event - Additional Information (Detail)	Jan. 08, 2020 USD ($) ft² Option	Dec. 31, 2019
Subsequent Event [Line Items]
Operating lease, existence of option to extend		true
Operating lease, existence of option to extend description		Lease terms may include options to extend or terminate when we are reasonably certain that the option will be exercised.
San Diego Lease with BRE CA Office Owner LLC \| Subsequent Event
Subsequent Event [Line Items]
Rentable area of building \| ft²	13,420
Lease commencement Date	May 01, 2020
Lease term period	5 years 4 months
Lease expiration date	Aug. 31, 2025
Operating lease, existence of option to extend	true
Operating lease, existence of option to extend description	we have a one-time option to extend the San Diego Lease for a period of five additional years.
Number of options to extend lease \| Option	1
Lease agreement additional extended lease term	5 years
Lease, monthly minimum rent payable	$ 58,000
Operating lease rate of increase in annual rent	3.00%
Lease allowance	$ 1,000,000.0

Recent Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Accounting Policies [Abstract]
Operating leases, right of use assets	$ 234	$ 600
Operating leases, liability	$ 252	$ 600

Stockholder's Equity - Additional Information (Detail) - USD ($)	1 Months Ended					12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jul. 31, 2018	Jan. 31, 2018	Aug. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Common stock, shares issued	6,785,000		4,600,000	3,136,722	8,805,000
Common stock, issued price per share	$ 17.00		$ 16.75		$ 6.50
Proceeds from issuance of common stock, net	$ 108,100,000		$ 74,500,000	$ 57,400,000	$ 53,500,000	$ 108,165,000	$ 132,172,000	$ 53,679,000
Common stock weighted-average per share				$ 18.85
SVB Leerink LLC and Stifel, Nicolaus & Company, Incorporated \| 2019 ATM Facility
Stockholders' Equity Note [Abstract]
Common stock, shares issued						0
SVB Leerink LLC and Stifel, Nicolaus & Company, Incorporated \| 2019 ATM Facility \| Maximum
Stockholders' Equity Note [Abstract]
Aggregate offering price		$ 75,000,000.0

Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets
Net operating loss carryforwards	$ 53,590	$ 37,329
Research and development tax credit carryforwards	4,748	3,140
Share-based compensation	2,134	1,426
Accruals	1,353	931
Intangibles	594	642
Other	171	131
Total deferred tax assets	62,590	43,599
Deferred tax liabilities	(165)
Less valuation allowance	(62,425)	(43,599)
Net deferred tax assets	$ 0	$ 0

Recent Accounting Pronouncements

12 Months Ended

Dec. 31, 2019

Accounting Changes And Error Corrections [Abstract]

Recent Accounting Pronouncements

3. Recent Accounting Pronouncements

Investments - Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Short-term investments, Fair Value	$ 210,756	$ 162,866
Fair Value Measurements on Recurring Basis
Schedule Of Available For Sale Securities [Line Items]
Short-term investments, Amortized Cost	210,425	162,994
Short-term investments, Unrealized Gains	331	6
Short-term investments, Unrealized Losses		(134)
Short-term investments, Fair Value	210,756	162,866
Cash equivalents and Short-term investments, Amortized Cost	228,870	171,502
Cash equivalents and Short-term investments, Unrealized Gains	331	6
Cash equivalents and Short-term investments, Unrealized Losses		(134)
Cash equivalents and Short-term investments, Fair Value	$ 229,201	$ 171,374
Fair Value Measurements on Recurring Basis \| Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	1 or less	1 or less
Cash equivalents, Amortized Cost	$ 18,445	$ 8,508
Cash equivalents, Fair Value	$ 18,445	$ 8,508
Fair Value Measurements on Recurring Basis \| Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	2 or less	1 or less
Short-term investments, Amortized Cost	$ 113,466	$ 56,779
Short-term investments, Unrealized Gains	182	6
Short-term investments, Unrealized Losses		(77)
Short-term investments, Fair Value	$ 113,648	$ 56,708
Fair Value Measurements on Recurring Basis \| U.S. Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	2 or less	1 or less
Short-term investments, Amortized Cost	$ 76,108	$ 39,780
Short-term investments, Unrealized Gains	149
Short-term investments, Unrealized Losses		(57)
Short-term investments, Fair Value	$ 76,257	$ 39,723
Fair Value Measurements on Recurring Basis \| Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	1 or less	1 or less
Short-term investments, Amortized Cost	$ 20,851	$ 66,435
Short-term investments, Fair Value	$ 20,851	$ 66,435

Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Results (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Information [Abstract]
Operating expenses	$ 18,963	$ 17,674	$ 15,891	$ 14,951	$ 16,634	$ 15,982	$ 15,276	$ 14,991	$ 67,479	$ 62,883	$ 36,077
Net loss	$ (17,865)	$ (16,392)	$ (14,943)	$ (13,940)	$ (16,097)	$ (15,007)	$ (14,739)	$ (14,604)	$ (63,140)	$ (60,447)	$ (35,434)
Net loss per share, basic and diluted	$ (0.39)	$ (0.36)	$ (0.38)	$ (0.37)	$ (0.42)	$ (0.40)	$ (0.45)	$ (0.46)	$ (1.51)	$ (1.72)	$ (1.52)
Weighted average number of shares used in computing net loss per share, basic and diluted	45,333	45,241	38,928	38,168	38,079	37,789	32,971	31,829	41,946	35,191	23,237

- Definition

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

+ References + Details

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Schedule of Operating Lease Expense

Operating lease expense was as follows, in thousands:

	Year Ended
	December 31, 2019
Operating lease cost	$	271
Operating lease cost, related party		232
Total operating lease costs	$	503

Schedule of Supplemental Cash Flow Information Related to Operating Leases

Supplemental cash flow information related to our operating leases was as follows, in thousands:

	Year Ended
	December 31, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	270
Operating cash flows from operating leases, related party		215
Total cash paid for amounts included in the measurement of lease liabilities	$	485

ROU assets obtained in exchange for operating lease liabilities	$	251
ROU assets obtained in exchange for operating lease liabilities, related party		221
Total ROU assets obtained in exchange for operating lease liabilities	$	472

Schedule of Supplemental Balance Sheet Information Related to Operating Leases

Supplemental balance sheet information related to our operating leases was as follows, in thousands (except lease term and discount rate):

	December 31, 2019
Operating lease ROU assets	$	155
Operating lease ROU assets, related party		79
Total operating lease ROU assets	$	234

Current lease liabilities	$	156
Current lease liabilities, related party		96
Total operating lease liabilities	$	252

Weighted-average remaining lease term (in years)		0.5
Weighted-average discount rate		6.5	%

Fair Value Measurements

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements

5. Fair Value Measurements

As of December 31, 2019 and 2018, we had cash equivalents and short-term investments measured at fair value on a recurring basis. The carrying amounts of our financial instruments, which include cash equivalents, prepaid expenses, accounts payable and accrued expenses approximate their fair values as of December 31, 2019 and 2018, primarily due to their short-term nature. Fair value estimates of these instruments are made at a specific point in time, based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision.

Available-for-sale marketable securities consist of U.S. Treasury securities, which were measured at fair value using Level 1 inputs, and corporate debt securities and commercial paper, which were measured at fair value using Level 2 inputs. We determine the fair value of Level 2 related securities with the aid of valuations provided by third parties using proprietary valuation models and analytical tools. These valuation models and analytical tools use market pricing or prices for similar instruments that are both objective and publicly available, including matrix pricing or reported trades, benchmark yields, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids and/or offers. We validate the fair values of Level 2 financial instruments by comparing these fair values to a third-party pricing source. No transfers between levels have occurred during the periods presented.

	December 31, 2019
	Balance		Level 1		Level 2
Cash equivalents:
Money market funds	$	18,445	$	18,445	$	—

Short-term investments:
Corporate debt securities		113,648		—		113,648
U.S. Treasury securities		76,257		76,257		—
Commercial paper		20,851		—		20,851
Total short-term investments		210,756		76,257		134,499
Total	$	229,201	$	94,702	$	134,499

	December 31, 2018
	Balance		Level 1		Level 2
Cash equivalents:
Money market funds	$	8,508	$	8,508	$	—

Short-term investments:
Corporate debt securities		56,708		—		56,708
U.S. Treasury securities		39,723		39,723		—
Commercial paper		66,435		—		66,435
Total short-term investments		162,866		39,723		123,143
Total	$	171,374	$	48,231	$	123,143

We believe that our term loan facility bears interest at a rate that approximates prevailing market rates for instruments with similar characteristics and, accordingly, the carrying value of the term loan facility approximates fair value. The fair value of our term loan facility is determined using Level 2 inputs in the fair value hierarchy. See Note 7, Long-Term Debt, for further details of our term loan facility.

Long-Term Debt - Additional Information (Detail) $ / shares in Units, $ in Thousands		12 Months Ended
	Nov. 01, 2018 USD ($)	Dec. 31, 2019 USD ($) MonthlyPayment $ / shares shares	Dec. 31, 2018 USD ($)	Apr. 30, 2016 USD ($)
Debt Instrument [Line Items]
Principal amount outstanding on loan		$ 7,500
Loss from extinguishment of debt			$ (498)
Oxford Finance LLC and Silicon Valley Bank \| Term Loan
Debt Instrument [Line Items]
Principal amount outstanding on loan				$ 7,500
Warrants issued to purchase of common stock \| shares		33,988
Warrants exercisable exercise price \| $ / shares		$ 3.31
Silicon Valley Bank \| Term Loan
Debt Instrument [Line Items]
Prepayment charge	$ 100
Maximum borrowing capacity under term loans	20,000
Additional borrowing description		Under the terms of the SVB Loan Agreement, we may, at our sole discretion, borrow from the Lender up to an additional $12.5 million at any time until May 1, 2020, or Term B Loan, and together with Term A Loan, the Term Loans. In addition, each Term B Loan must be in an amount equal to the lesser of $5.0 million or the amount that is remaining under the Term B Loan.
Loss from extinguishment of debt			$ (500)
Term loan facility maturity date		May 01, 2023
Description of term loan payment terms		All of the Term Loans will be due on the scheduled maturity date of May 1, 2023, or Maturity Date. Repayment of the Term Loans will be interest only through November 30, 2020, followed by 30 equal monthly payments of principal plus accrued interest commencing on December 1, 2020.
Number of equal monthly payments of principal and accrued interest \| MonthlyPayment		30
Frequency of periodic payment		monthly
Principal and interest payments commencement date		Dec. 01, 2020
Debt instrument, interest rate		5.50%
Final payment as a percentage of amounts borrowed		7.75%
Team loan interest rate description		The per annum interest rate for any outstanding Term Loans is the greater of (i) 5.50% and (ii) the sum of (a) the prime rate reported in The Wall Street Journal plus (b) 0.25%.
Silicon Valley Bank \| Term Loan \| Prime Rate
Debt Instrument [Line Items]
Percentage of prime rate included in effective interest rate		0.25%
Silicon Valley Bank \| Term Loan \| Transaction Occurring Assumption One
Debt Instrument [Line Items]
Prepayment fee equal to outstanding principal amount		1.00%
Silicon Valley Bank \| Term Loan \| Transaction Occurring Assumption Two
Debt Instrument [Line Items]
Prepayment fee equal to outstanding principal amount		2.00%
Silicon Valley Bank \| Term Loan \| Minimum \| Base Rate
Debt Instrument [Line Items]
Debt instrument, interest rate		5.50%
Silicon Valley Bank \| Term A Loan
Debt Instrument [Line Items]
Principal amount outstanding on loan	7,500
Repayment of Oxford Finance LLC and Silicon Valley Bank debt	6,900
Silicon Valley Bank \| Term B Loan
Debt Instrument [Line Items]
Term loan unused facility	12,500
Minimum draw amount	$ 5,000