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Share-Based Compensation - Additional Information (Detail) - Employee Stock Option $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized Expense	$ 30.5
Weighted average service period	3 years

Condensed Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 33,811	$ 26,135
Short-term investments	183,124	210,756
Accounts receivable, related party	31	30
Prepaid expenses and other current assets	4,164	2,682
Total current assets	221,130	239,603
Property and equipment, net	805	44
Restricted cash	210
Other long-term assets	4,317	2,325
Total assets	226,462	241,972
Current liabilities:
Accounts payable and accrued expenses	13,554	15,314
Current portion of long-term debt, net	1,000	250
Total current liabilities	14,554	15,564
Long-term debt, net	6,500	7,250
Other long-term liabilities	2,207	377
Total liabilities	23,261	23,191
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; 45,430 and 45,384 shares issued and outstanding as of March 31, 2020 and December 31, 2019, respectively	5	5
Additional paid-in capital	434,722	431,322
Accumulated other comprehensive income	561	331
Accumulated deficit	(232,087)	(212,877)
Total stockholders' equity	203,201	218,781
Total liabilities and stockholders' equity	$ 226,462	$ 241,972

Condensed Statements of Operations and Comprehensive Loss (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Research and development, related party	$ 132	$ 53
General and administrative, related party	$ 111	$ 87

Organization and Basis of Presentation

3 Months Ended

Mar. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Basis of Presentation

1. Organization and Basis of Presentation

The Company

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 Unaudited Condensed Financial Statements to the “Company,” “we,” “our” or “us,” refer to Kura Oncology, Inc.

Basis of Presentation

The accompanying unaudited condensed financial statements should be read in conjunction with the audited financial statements and notes thereto in our Annual Report on Form 10-K for the fiscal year ended December 31, 2019, as filed with the Securities and Exchange Commission on February 25, 2020, from which we derived our balance sheet as of December 31, 2019. The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP, for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, since they are interim statements, the accompanying unaudited condensed financial statements do not include all of the information and notes required by GAAP for complete financial statements. The accompanying unaudited condensed financial statements reflect all adjustments, consisting of normal recurring adjustments, that are, in the opinion of our management, necessary to a fair statement of the results for the interim periods presented. Interim results are not necessarily indicative of results for a full year.

The preparation of the unaudited condensed financial statements in accordance with GAAP requires our management to make estimates and assumptions that affect the amounts reported on our unaudited condensed financial statements and accompanying notes. The amounts reported could differ under different estimates and assumptions. On an ongoing basis, we evaluate our estimates and judgments, which are based on historical and anticipated results and trends and on various other assumptions that management believes to be reasonable under the circumstances. Though the impact of the COVID-19 pandemic to our business and operating results presents additional uncertainty, we continue to use the best information available to inform our critical accounting estimates. By their nature, estimates are subject to an inherent degree of uncertainty and, as such, actual results may differ from management’s estimates.

The extent to which the COVID-19 pandemic may impact our business will depend on future developments, which are highly uncertain and cannot be predicted with any confidence, such as the duration and severity of the COVID-19 pandemic, steps required or mandated by governments to mitigate the impact of COVID-19 or the effectiveness of actions to prevent, contain and treat COVID-19, particularly in the geographies where we, our third party manufacturers, contract research organizations or current and planned clinical trial sites operate. We cannot presently predict the scope and severity of any potential business disruptions, interruptions or shutdowns. If we or any of the third parties with whom we engage, however, were to experience shutdowns or other business disruptions, our ability to conduct our business in the manner and on the timelines presently planned could be materially and negatively affected, which could have a material adverse impact on our business and our results of operation and financial condition.

Related Party Transactions

3 Months Ended

Mar. 31, 2020

Related Party Transactions

8. Related Party Transactions

Our president and chief executive officer is also the sole managing member of Araxes Pharma LLC, or Araxes, and is a significant stockholder of each of us and Araxes. The following is a summary of related party transactions for the three months ended March 31, 2020 and 2019:

•

Facility Sublease

We subleased office space in San Diego, California from Araxes pursuant to the Sublease. The Sublease commenced in June 2017 and would have expired on October 31, 2019. In March 2019, the Sublease was amended to extend until April 30, 2020, and the monthly rent increased to approximately $24,000 per month effective November 1, 2019, corresponding to the increase in Araxes’ monthly rent. In April 2020, the Sublease was amended to extend the expiration date to June 30, 2020 with no change to the amount of monthly rent. For the three months ended March 31, 2020 and 2019, rent expense, including operating costs, related to our sublease was approximately $0.1 million in both periods.

•

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 three months ended March 31, 2020 and 2019, we recorded approximately $0.1 million in management fee income in both periods. 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 $382,000, 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 three months ended March 31, 2020 and 2019, we recorded reimbursements of nil and approximately $0.1 million, respectively, for research and development services

provided to Araxes, which was recorded as a reduction to research and development expenses, on our unaudited condensed statements of operations and comprehensive loss. As of March 31, 2020 and December 31, 2019, approximately $0.1 million in both periods related to management fees and reimbursements of research and development services, which are included in accounts receivable, related party on our unaudited condensed balance sheets.

•

Services Agreement

We have a services agreement with Wellspring Biosciences, Inc., or 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 three months ended March 31, 2020 and 2019, we recognized approximately $0.1 million in both periods, from research and development services provided to us under this agreement as research and development expense on our unaudited condensed statements of operations and comprehensive loss. As of March 31, 2020 and December 31, 2019, approximately $0.1 million and nil, respectively, related to research and development services under this agreement, which are included in accounts payable and accrued expenses on our unaudited condensed balance sheets.

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Summary Of Significant Accounting Policies [Line Items]
Restricted cash pledged as collateral	$ 210
Total potentially dilutive securities	5,368,000	4,383,000
Collateral Pledged
Summary Of Significant Accounting Policies [Line Items]
Restricted cash pledged as collateral	$ 200

Share-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Share-based Compensation Expense

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

	Three Months Ended March 31,
	2020		2019
Research and development	$	1,170	$	797
General and administrative		1,983		1,472
Total share-based compensation expense	$	3,153	$	2,269

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the unaudited condensed balance sheets that sum to the total of the amounts shown in the unaudited condensed statements of cash flows, in thousands:

	March 31, 2020		December 31, 2019		March 31, 2019		December 31, 2018
Cash and cash equivalents	$	33,811	$	26,135	$	17,778	$	16,119
Restricted cash		210		—		—		—
Total	$	34,021	$	26,135	$	17,778	$	16,119

Leases

3 Months Ended

Mar. 31, 2020

Leases [Abstract]

Leases

6. Leases

We have a sublease with a related party for office space in San Diego, California, or Sublease, and a lease for office space in Cambridge, Massachusetts, that existed before January 1, 2019 and were classified as operating leases. In March 2019, the Sublease was amended to extend the expiration date from October 31, 2019 to April 30, 2020 with the monthly rent increased from approximately $16,000 to approximately $24,000 per month effective November 1, 2019. In April 2020, the Sublease was amended to extend the expiration date from April 30, 2020 to June 30, 2020 with no change to the amount of monthly rent. See Note 8, Related Party Transactions, for further details of the Sublease.

In January 2020, we entered into an office lease agreement for our future corporate offices in San Diego, California, or San Diego Lease, which would have commenced on May 1, 2020. In May 2020, the commencement date has subsequently been amended to August 1, 2020, as described in Note 9, Subsequent Events. The San Diego Lease term is five years and four months and provides for a one-time option to extend for a period of five additional years. The monthly base rent is approximately $58,000 for the first year, which amount will increase by 3.0% per year over the initial term. In addition, the lease is subject to charges for common area maintenance and other costs. The lease provides four month rent abatement periods during the first year of the lease and approximately $1.0 million in reimbursement for allowable tenant improvements, which effectively reduce the total lease payments owed for the lease. The San Diego Lease is considered to be an operating lease. For accounting purposes, the lease commencement date was determined to be March 2020 when we had control of the office space. We recorded operating lease right-of-use, or ROU, asset and operating lease liability of approximately $2.2 million on our unaudited condensed balance sheet.

In March 2020, we entered into a lease for office space in Boston, Massachusetts, or the Boston Lease, commencing on April 1, 2020 and expiring on July 31, 2024. The lease provides for one option to extend the lease for a period of five additional years. The monthly base rent will be approximately $105,500 for the first year, which amount will increase by 2.0% per year over the initial term. In addition to base monthly rent, we will be obligated to pay for common area maintenance and other costs. Under the terms of the Boston Lease, we are required to maintain a standby letter of credit of approximately $0.2 million during the term of the lease. As of March 31, 2020, we had not taken control of the space and the lease term had not commenced; therefore, no ROU asset or lease liability has been recorded.

Maturities of lease liabilities as of March 31, 2020 are as follows, in thousands:

Year Ending December 31,
2020 (remaining)*	$	(739	)
2021		706
2022		728
2023		749
2024		772
2025		527
Total lease payments		2,743
Less: imputed interest		(526	)
Total operating lease liabilities	$	2,217

*	Includes tenant incentives of $1.0 million to be received from the landlord in 2020.

As of December 31, 2019, we had remaining lease liabilities of approximately $0.3 million which will mature in 2020. ROU assets are recorded in other long-term assets on our unaudited condensed balance sheets. Current and non-current lease

liabilities are recorded in accounts payable and accrued expenses and other long-term liabilities, respectively, on our unaudited condensed balance sheets. As of March 31, 2020 and December 31, 2019, total operating lease ROU assets were $2.2 million and $0.2 million, respectively. As of March 31, 2020 and December 31, 2019, total operating lease liabilities were $2.2 million and $0.3 million, respectively, $1.8 million of which was recorded as noncurrent lease liability as of March 31, 2020. As of March 31, 2020 and December 31, 2019, the weighted-average discount rate was 5.6% and 6.5%, respectively. As of March 31, 2020 and December 31, 2019, the weighted-average remaining lease term was 5.2 years and 0.5 years, respectively.

Total cash paid for amounts included in the measurement of lease liabilities was $0.2 million and $0.1 million for the three months ended March 31, 2020 and 2019, respectively. ROU assets obtained in exchange for operating lease liabilities were $2.2 million and $0.7 million for the three months ended March 31, 2020 and 2019, respectively.

Total operating lease expense was approximately $0.2 million and $0.1 million for the three months ended March 31, 2020 and 2019, respectively. We have entered into short-term operating leases that are not recorded on the unaudited condensed balance sheet. Total rent expense of all operating leases for the three months ended March 31, 2020 and 2019 was approximately $0.3 million and $0.1 million, respectively.

Balance Sheet Detail (Tables)

3 Months Ended

Mar. 31, 2020

Balance Sheet Related Disclosures [Abstract]

Summary of Property and Equipment

Property and equipment consisted of the following, in thousands:

	March 31, 2020			December 31, 2019
Computer software and equipment and laboratory equipment	$	136		$	136
Furniture and fixtures		511			—
Leasehold improvements		250			—
Property and equipment, gross		897			136
Less: accumulated depreciation		(92	)		(92	)
Property and equipment, net	$	805		$	44

Summary of Accounts Payable and Accrued Liabilities

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

	March 31, 2020		December 31, 2019
Accounts payable	$	2,453	$	3,526
Accrued research and development expenses		7,052		6,970
Accrued compensation and benefits		2,088		3,694
Other accrued expenses		1,961		1,124
Total accounts payable and accrued expenses	$	13,554	$	15,314

Share-Based Compensation

3 Months Ended

Mar. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-Based Compensation

7. Share-Based Compensation

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

	Three Months Ended March 31,
	2020		2019
Research and development	$	1,170	$	797
General and administrative		1,983		1,472
Total share-based compensation expense	$	3,153	$	2,269

As of March 31, 2020, unrecognized compensation costs related to employee stock options was approximately $30.5 million, which is expected to be recognized over a weighted average period of approximately 3.0 years.

Share-Based Compensation - Summary of Share-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 3,153	$ 2,269
Research and development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	1,170	797
General and administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 1,983	$ 1,472

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2020	Apr. 30, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Trading Symbol	KURA
Entity Registrant Name	KURA ONCOLOGY, INC.
Entity Central Index Key	0001422143
Entity Current Reporting Status	Yes
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 Common Stock, Shares Outstanding		45,436,664
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 Quarterly Report	true
Document Transition Report	false

Leases - Additional Information (Detail)					1 Months Ended				3 Months Ended
Leases - Additional Information (Detail)	Apr. 22, 2020	Oct. 31, 2019 USD ($)	Mar. 05, 2019 USD ($)	Jun. 01, 2017	Apr. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) Option	Jan. 31, 2020 USD ($) Option	Mar. 31, 2019	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Lessee Lease Description [Line Items]
Lease allowance						$ 1,000,000.0			$ 1,000,000.0
Operating leases, right of use assets						2,200,000			2,200,000		$ 200,000
Operating leases, liability						2,217,000			2,217,000		300,000
Remaining lease liabilities											$ 300,000
Noncurrent lease liability						$ 1,800,000			$ 1,800,000
Weighted-average discount rate						5.60%			5.60%		6.50%
Weighted-average remaining lease term						5 years 2 months 12 days			5 years 2 months 12 days		6 months
Total cash paid for amounts included in the measurement of lease liabilities									$ 200,000	$ 100,000
ROU assets obtained in exchange for operating lease liabilities									2,200,000	700,000
Total operating lease rent expense									300,000	100,000
ASC 842
Lessee Lease Description [Line Items]
Total operating lease rent expense									$ 200,000	$ 100,000
San Diego Lease
Lessee Lease Description [Line Items]
Lease commencement date							May 01, 2020
Lease commencement amendment date							Aug. 01, 2020
Lessee operating lease term of contract							5 years 4 months
Operating lease, existence of option to extend							true
Description of operating lease, option to extend							a one-time option to extend 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
Operating leases, right of use assets							2,200,000
Operating leases, liability							$ 2,200,000
Boston Lease
Lessee Lease Description [Line Items]
Lease commencement date						Apr. 01, 2020
Operating lease, existence of option to extend						true
Description of operating lease, option to extend						one option to extend the lease for a period of five additional years
Number of options to extend lease \| Option						1
Lease agreement additional extended lease term						5 years			5 years
Lease, monthly minimum rent payable						$ 105,500
Operating lease rate of increase in annual rent						2.00%
Lease expiration date						Jul. 31, 2024
Boston Lease \| Letter of Credit
Lessee Lease Description [Line Items]
Letter of Credit						$ 200,000			$ 200,000
Araxes Pharma LLC \| San Diego, California
Lessee Lease Description [Line Items]
Sublease expiration date			Oct. 31, 2019	Oct. 31, 2019
Sublease extended expiration date			Apr. 30, 2020					Apr. 30, 2020
Amended sublease effective date			Nov. 01, 2019
Araxes Pharma LLC \| San Diego, California \| Subsequent Event
Lessee Lease Description [Line Items]
Sublease extended expiration date	Jun. 30, 2020				Jun. 30, 2020
Araxes Pharma LLC \| San Diego, California \| Monthly
Lessee Lease Description [Line Items]
Rent expense		$ 16,000	$ 24,000
Araxes Pharma LLC \| San Diego, California \| Monthly \| Subsequent Event
Lessee Lease Description [Line Items]
Amended change in amount of rent expense					$ 0

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2020

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:

	March 31, 2020
	Balance		Level 1		Level 2
Cash equivalents:
Money market funds	$	30,881	$	30,881	$	—

Short-term investments:
Corporate debt securities		84,150	—			84,150
U.S. Treasury securities		71,698		71,698		—
Commercial paper		27,276		—		27,276
Total short-term investments		183,124		71,698		111,426
Total	$	214,005	$	102,579	$	111,426

	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

Condensed Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
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	45,430,000	45,384,000
Common stock, shares outstanding	45,430,000	45,384,000

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating Activities
Net loss	$ (19,210)	$ (13,940)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	3,153	2,269
Amortization of premium and accretion of discount on marketable securities, net	(110)	(540)
Changes in operating assets and liabilities:
Accounts receivable, related party	(1)	45
Prepaid expenses and other current assets	(1,482)	146
Other long-term assets	160	(182)
Accounts payable and accrued expenses	(2,391)	(2,065)
Other long-term liabilities	59	16
Net cash used in operating activities	(19,822)	(14,251)
Investing Activities
Maturities and sales of marketable securities	39,246	66,656
Purchases of marketable securities	(11,274)	(50,848)
Purchases of property and equipment	(511)
Net cash provided by investing activities	27,461	15,808
Financing Activities
Proceeds from exercise of stock options	247	102
Net cash provided by financing activities	247	102
Net increase in cash, cash equivalents and restricted cash	7,886	1,659
Cash, cash equivalents and restricted cash at beginning of period	26,135	16,119
Cash, cash equivalents and restricted cash at end of period	$ 34,021	$ 17,778

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Cash and cash equivalents	$ 33,811	$ 26,135	$ 17,778	$ 16,119
Restricted cash	210
Total	$ 34,021	$ 26,135	$ 17,778	$ 16,119

Leases - Schedule of Maturities of Lease Liabilities (Parenthetical)(Detail) $ in Millions	Mar. 31, 2020 USD ($)
Leases [Abstract]
Tenant Incentives	$ 1.0

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Reclassifications

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

Restricted Cash

Under the terms of an office lease entered into in March 2020, we are required to maintain a standby letter of credit during the term of the lease. As of March 31, 2020, restricted cash of $0.2 million was pledged as collateral for the letter of credit.

	March 31, 2020		December 31, 2019		March 31, 2019		December 31, 2018
Cash and cash equivalents	$	33,811	$	26,135	$	17,778	$	16,119
Restricted cash		210		—		—		—
Total	$	34,021	$	26,135	$	17,778	$	16,119

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, 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 antidilutive effect of the securities. More specifically, for the three months ended March 31, 2020 and 2019, outstanding stock options, an outstanding warrant and employee stock purchase plan rights totaling approximately 5,368,000 shares and 4,383,000 shares, respectively, were excluded from the calculation of diluted net loss per share because to do so would be anti-dilutive.

Recent Accounting Pronouncements

In June 2016, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments, in order to improve financial reporting of expected credit losses on financial instruments and other commitments to extend credit. ASU 2016-13 requires that an entity measure and recognize expected credit losses for financial assets held at amortized cost and replaces the incurred loss impairment methodology in prior GAAP with a methodology that requires consideration of a broader range of information to estimate credit losses, and establishes additional disclosures related to credit risks. We adopted ASU 2016-13 on January 1, 2020. The adoption of the new standard did not have a material impact on our unaudited condensed financial statements. We will continue to actively monitor the impact of the recent coronavirus (COVID-19) pandemic on expected credit losses.

Investments - Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Short-term investments, Fair Value	$ 183,124	$ 210,756
Fair Value Measurements on Recurring Basis
Schedule Of Available For Sale Securities [Line Items]
Short-term investments, Amortized Cost	182,563	210,425
Short-term investments, Unrealized Gains	650	331
Short-term investments, Unrealized Losses	(89)
Short-term investments, Fair Value	183,124	210,756
Cash equivalents and Short-term investments, Amortized Cost	213,444	228,870
Cash equivalents and Short-term investments, Unrealized Gains	650	331
Cash equivalents and Short-term investments, Unrealized Losses	(89)
Cash equivalents and Short-term investments, Fair Value	$ 214,005	$ 229,201
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	$ 30,881	$ 18,445
Cash equivalents, Fair Value	$ 30,881	$ 18,445
Fair Value Measurements on Recurring Basis \| Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	2 or less	2 or less
Short-term investments, Amortized Cost	$ 84,224	$ 113,466
Short-term investments, Unrealized Gains	15	182
Short-term investments, Unrealized Losses	(89)
Short-term investments, Fair Value	$ 84,150	$ 113,648
Fair Value Measurements on Recurring Basis \| U.S. Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	2 or less	2 or less
Short-term investments, Amortized Cost	$ 71,063	$ 76,108
Short-term investments, Unrealized Gains	635	149
Short-term investments, Fair Value	$ 71,698	$ 76,257
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	$ 27,276	$ 20,851
Short-term investments, Fair Value	$ 27,276	$ 20,851

Subsequent Events

3 Months Ended

Mar. 31, 2020

Subsequent Events [Abstract]

Subsequent Events

9. Subsequent Events

On April 3, 2020, we entered into the First Amendment to Loan and Security Agreement with Silicon Valley Bank to extend the additional draw period. Under the terms of the loan and security agreement, as amended, we may, at our sole discretion, borrow up to an additional $12.5 million at any time until November 30, 2020.

On April 22, 2020, we entered into a Second Amendment to Sublease with Araxes to extend the expiration of the Sublease to June 30, 2020.

On May 2, 2020, we entered into a First Amendment to the San Diego Lease, to amend the commencement date from May 1, 2020 to August 1, 2020.

Leases (Tables)

3 Months Ended

Mar. 31, 2020

Leases [Abstract]

Schedule of Maturities of Lease Liabilities

Maturities of lease liabilities as of March 31, 2020 are as follows, in thousands:

Year Ending December 31,
2020 (remaining)*	$	(739	)
2021		706
2022		728
2023		749
2024		772
2025		527
Total lease payments		2,743
Less: imputed interest		(526	)
Total operating lease liabilities	$	2,217

*	Includes tenant incentives of $1.0 million to be received from the landlord in 2020.

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating Expenses:
Research and development (includes related party amounts of $132 and $53 for the three months ended March 31, 2020 and 2019, respectively)	$ 12,575	$ 10,382
General and administrative (includes related party amounts of $111 and $87 for the three months ended March 31, 2020 and 2019, respectively)	7,625	4,569
Total operating expenses	20,200	14,951
Other Income (Expense):
Management fee income, related party	15	126
Interest income	1,119	1,030
Interest expense	(144)	(145)
Total other income	990	1,011
Net Loss	$ (19,210)	$ (13,940)
Net loss per share, basic and diluted	$ (0.42)	$ (0.37)
Weighted average number of shares used in computing net loss per share, basic and diluted	45,411	38,168
Comprehensive Loss:
Net loss	$ (19,210)	$ (13,940)
Other comprehensive income:
Unrealized gain on marketable securities and foreign currency	230	149
Comprehensive Loss	$ (18,980)	$ (13,791)

Investments (Tables)

3 Months Ended

Mar. 31, 2020

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:

		March 31, 2020
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	1 or less	$	30,881	$	—	$	—		$	30,881

Short-term investments:
Corporate debt securities	2 or less		84,224		15		(89	)		84,150
U.S. Treasury securities	2 or less		71,063		635		—			71,698
Commercial paper	1 or less		27,276		—		—			27,276
Total short-term investments			182,563		650		(89	)		183,124
Total		$	213,444	$	650	$	(89	)	$	214,005

		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

Fair Value Measurements - Schedule Of Fair Value Measurements, By Major Security Type (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 183,124	$ 210,756
Fair Value Measurements on Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	183,124	210,756
Cash equivalents and short-term investments	214,005	229,201
Fair Value Measurements on Recurring Basis \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	71,698	76,257
Cash equivalents and short-term investments	102,579	94,702
Fair Value Measurements on Recurring Basis \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	111,426	134,499
Cash equivalents and short-term investments	111,426	134,499
Fair Value Measurements on Recurring Basis \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	30,881	18,445
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	30,881	18,445
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	84,150	113,648
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	84,150	113,648
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	71,698	76,257
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	71,698	76,257
Fair Value Measurements on Recurring Basis \| Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	27,276	20,851
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	$ 27,276	$ 20,851

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2020

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.

Restricted Cash

	March 31, 2020		December 31, 2019		March 31, 2019		December 31, 2018
Cash and cash equivalents	$	33,811	$	26,135	$	17,778	$	16,119
Restricted cash		210		—		—		—
Total	$	34,021	$	26,135	$	17,778	$	16,119

Net Loss per Share

Recent Accounting Pronouncements

Fair Value Measurements

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

4. Fair Value Measurements

As of March 31, 2020 and December 31, 2019, we had cash equivalents and short-term investments measured at fair value on a recurring basis. 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.

	March 31, 2020
	Balance		Level 1		Level 2
Cash equivalents:
Money market funds	$	30,881	$	30,881	$	—

Short-term investments:
Corporate debt securities		84,150	—			84,150
U.S. Treasury securities		71,698		71,698		—
Commercial paper		27,276		—		27,276
Total short-term investments		183,124		71,698		111,426
Total	$	214,005	$	102,579	$	111,426

	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

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.

Balance Sheet Detail - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 897	$ 136
Less: accumulated depreciation	(92)	(92)
Property and equipment, net	805	44
Computer Software and Equipment and Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	136	$ 136
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	511
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 250

Investments - Additional Information (Detail)	3 Months Ended
Investments - Additional Information (Detail)	Mar. 31, 2020 USD ($)
Investments All Other Investments [Abstract]
Short-term investments maturities, description	As of March 31, 2020, $173.0 million of our short-term investments had maturities less than one year, and $10.1 million had maturities between one to two years.
Short-term investments with maturities less than one year	$ 173,000,000.0
Short-term investments with maturities between one to two years	10,100,000
Allowance for credit losses	$ 0

Condensed Statements of Stockholders' Equity (Unaudited) - 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, 2018	$ 160,985	$ 4	$ 310,849	$ (131)	$ (149,737)
Beginning balance (in shares) at Dec. 31, 2018		38,148
Share-based compensation expense	2,269		2,269
Issuance of common stock from exercise of options	102		102
Issuance of common stock from exercise of options (in shares)		21
Other comprehensive income	149			149
Net loss	(13,940)				(13,940)
Ending balance at Mar. 31, 2019	149,565	$ 4	313,220	18	(163,677)
Ending balance (in shares) at Mar. 31, 2019		38,169
Beginning balance at Dec. 31, 2019	218,781	$ 5	431,322	331	(212,877)
Beginning balance (in shares) at Dec. 31, 2019		45,384
Share-based compensation expense	3,153		3,153
Issuance of common stock from exercise of options	247		247
Issuance of common stock from exercise of options (in shares)		46
Other comprehensive income	230			230
Net loss	(19,210)				(19,210)
Ending balance at Mar. 31, 2020	$ 203,201	$ 5	$ 434,722	$ 561	$ (232,087)
Ending balance (in shares) at Mar. 31, 2020		45,430

- Definition

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

+ References + Details

Leases - Schedule of Maturities of Lease Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2020 (remaining)*	$ (739)
2021	706
2022	728
2023	749
2024	772
2025	527
Total lease payments	2,743
Less: imputed interest	(526)
Total operating lease liabilities	$ 2,217	$ 300

Related Party Transactions - Additional Information (Detail) - USD ($)						1 Months Ended		3 Months Ended
	Apr. 22, 2020	Mar. 05, 2019	Jun. 01, 2017	Apr. 30, 2016	Oct. 01, 2014	Apr. 30, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Rent expense related to office space sublease								$ 300,000	$ 100,000
Management fee income								15,000	126,000
Accounts receivable, related party								31,000		$ 30,000
Research and development, related party								$ 132,000	53,000
Araxes Pharma LLC \| Management Fees
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 $382,000, 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								$ 100,000	100,000
Service Agreement for research and development				$ 382,000
Agreement expiration date					Dec. 31, 2015
Agreement termination notice period					30 days
Reimbursements of research and development services									100,000
Accounts receivable, related party								100,000		$ 100,000
Araxes Pharma LLC \| San Diego, California
Related Party Transaction [Line Items]
Sublease commencement date			Jun. 30, 2017
Sublease expiration date		Oct. 31, 2019	Oct. 31, 2019
Sublease extended expiration date		Apr. 30, 2020					Apr. 30, 2020
Amended sublease effective date							Nov. 01, 2019
Araxes Pharma LLC \| San Diego, California \| Monthly
Related Party Transaction [Line Items]
Rent expense, amended sublease							$ 24,000
Araxes Pharma LLC \| San Diego, California \| Sublease
Related Party Transaction [Line Items]
Rent expense related to office space sublease								$ 100,000	100,000
Wellspring Biosciences Inc \| Service Agreements
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 Biosciences, Inc., or 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								$ 100,000	$ 100,000
Accrued expenses								$ 100,000
Subsequent Event \| Araxes Pharma LLC \| San Diego, California
Related Party Transaction [Line Items]
Sublease extended expiration date	Jun. 30, 2020					Jun. 30, 2020
Subsequent Event \| Araxes Pharma LLC \| San Diego, California \| Monthly
Related Party Transaction [Line Items]
Amended change in amount of rent expense						$ 0

Investments

3 Months Ended

Mar. 31, 2020

Investments All Other Investments [Abstract]

Investments

3. 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 our unaudited condensed balance sheets.

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

		March 31, 2020
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	1 or less	$	30,881	$	—	$	—		$	30,881

Short-term investments:
Corporate debt securities	2 or less		84,224		15		(89	)		84,150
U.S. Treasury securities	2 or less		71,063		635		—			71,698
Commercial paper	1 or less		27,276		—		—			27,276
Total short-term investments			182,563		650		(89	)		183,124
Total		$	213,444	$	650	$	(89	)	$	214,005

		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

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 March 31, 2020, $173.0 million of our short-term investments had maturities less than one year, and $10.1 million had maturities between one to two years. Realized gains and losses were de minimus for the three months ended March 31, 2020.

We evaluate our available-for-sale debt securities for credit losses when the amortized cost basis exceeds fair value. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in interest income through an allowance account. Unrealized gains and losses that are not credit-related are included in accumulated other comprehensive income (loss). When evaluating an investment for impairment, we review factors such as the severity of the impairment, changes in underlying credit ratings, forecasted recovery, our intent to sell or the likelihood that we would be required to sell the investment before its anticipated recovery in market value and the probability that the scheduled cash payments will continue to be made. We recorded no allowance for credit losses in the statement of operations and comprehensive loss during the three months ended March 31, 2020.

Subsequent Events - Additional Information (Detail) - USD ($) $ in Millions					1 Months Ended
	May 02, 2020	Apr. 22, 2020	Apr. 03, 2020	Mar. 05, 2019	Apr. 30, 2020	Mar. 31, 2019
Araxes Pharma LLC \| San Diego, California
Subsequent Event [Line Items]
Sublease extended expiration date				Apr. 30, 2020		Apr. 30, 2020
Subsequent Event \| Araxes Pharma LLC \| San Diego, California
Subsequent Event [Line Items]
Sublease extended expiration date		Jun. 30, 2020			Jun. 30, 2020
Subsequent Event \| First Amendment \| San Diego, California
Subsequent Event [Line Items]
Lease commencement amendment date	Aug. 01, 2020
Subsequent Event \| First Amendment \| Silicon Valley Bank
Subsequent Event [Line Items]
Term loan unused facility			$ 12.5
Discretionary extended draw period date			Nov. 30, 2020

Balance Sheet Detail - Summary of Accounts Payable and Accrued Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accounts payable	$ 2,453	$ 3,526
Accrued research and development expenses	7,052	6,970
Accrued compensation and benefits	2,088	3,694
Other accrued expenses	1,961	1,124
Total accounts payable and accrued expenses	$ 13,554	$ 15,314

Balance Sheet Detail

3 Months Ended

Mar. 31, 2020

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Detail

5. Balance Sheet Detail

Property and equipment consisted of the following, in thousands:

	March 31, 2020			December 31, 2019
Computer software and equipment and laboratory equipment	$	136		$	136
Furniture and fixtures		511			—
Leasehold improvements		250			—
Property and equipment, gross		897			136
Less: accumulated depreciation		(92	)		(92	)
Property and equipment, net	$	805		$	44

Furniture and fixtures and leasehold improvements are being constructed for our new office facilities and have not been placed into service as of March 31, 2020.

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

	March 31, 2020		December 31, 2019
Accounts payable	$	2,453	$	3,526
Accrued research and development expenses		7,052		6,970
Accrued compensation and benefits		2,088		3,694
Other accrued expenses		1,961		1,124
Total accounts payable and accrued expenses	$	13,554	$	15,314