Kura Oncology (KURA) 10-K 12 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Mar. 09, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	KURA
Entity Registrant Name	Kura Oncology, Inc.
Entity Central Index Key	1,422,143
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Smaller Reporting Accelerated Filer
Entity Public Float			$ 157.1
Entity Common Stock, Shares Outstanding		33,353,809

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 11,433	$ 9,725
Short-term investments	81,712	58,065
Accounts receivable, related party	216	295
Prepaid expenses and other current assets	1,280	725
Total current assets	94,641	68,810
Property and equipment, net	10	40
Other long-term assets	1,200	971
Total assets	95,851	69,821
Current liabilities:
Accounts payable and accrued expenses	8,284	4,681
Accounts payable and accrued expenses, related party	216	770
Current portion of long-term debt, net	1,531
Total current liabilities	10,031	5,451
Long-term debt, net	5,567	7,324
Other long-term liabilities	388	170
Total liabilities	15,986	12,945
Commitments and contingencies (Note 10)
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; 30,217 and 21,368 shares issued as of December 31, 2017 and 2016, respectively; and 29,424 and 19,348 shares outstanding as of December 31, 2017 and 2016, respectively, excluding 793 and 2,020 shares subject to repurchase as of December 31, 2017 and 2016, respectively	3	2
Additional paid-in capital	169,201	110,748
Accumulated other comprehensive loss	(49)	(18)
Accumulated deficit	(89,290)	(53,856)
Total stockholders' equity	79,865	56,876
Total liabilities and stockholders' equity	$ 95,851	$ 69,821

BALANCE SHEETS (Parenthetical)

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
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	30,217,000	21,368,000
Common stock, shares outstanding	29,424,000	19,348,000
Number of shares, subject to repurchase	792,765	2,020,000

STATEMENTS OF OPERATIONS AND CO

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating Expenses:
Research and development	$ 25,114	$ 16,575
Research and development, related party	1,312	3,829
General and administrative	9,404	7,861
General and administrative, related party	247	102
Total operating expenses	36,077	28,367
Other Income (Expense):
Management fee income, related party	780	885
Interest income	751	499
Interest expense	(888)	(577)
Total other income	643	807
Net loss	$ (35,434)	$ (27,560)
Net loss per share, basic and diluted	$ (1.52)	$ (1.47)
Weighted average number of shares used in computing net loss per share, basic and diluted	23,237	18,701
Comprehensive Loss:
Net loss	$ (35,434)	$ (27,560)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities	(31)	69
Comprehensive loss	$ (35,465)	$ (27,491)

STATEMENTS OF STOCKHOLDERS' EQU

STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid- In Capital	Unrealized Gain (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2015	$ 82,103	$ 2	$ 108,484	$ (87)	$ (26,296)
Beginning balance (in shares) at Dec. 31, 2015		18,138
Restricted stock awards vested	3		3
Restricted stock awards vested (in shares)		1,210
Share-based compensation expense	2,089		2,089
Unrealized gain (loss) on marketable securities	69			69
Issuance of warrants in connection with debt facility	172		172
Net loss	(27,560)				(27,560)
Ending balance at Dec. 31, 2016	56,876	$ 2	110,748	(18)	(53,856)
Ending balance (in shares) at Dec. 31, 2016		19,348
Restricted stock awards vested	3		3
Restricted stock awards vested (in shares)		1,193
Share-based compensation expense	4,545		4,545
Unrealized gain (loss) on marketable securities	(31)			(31)
Issuance of common stock from exercise of options	232		232
Issuance of common stock from exercise of options (in shares)		47
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
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

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating Activities
Net loss	$ (35,434)	$ (27,560)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	4,545	2,089
Non-cash interest expense	118	42
Depreciation expense	30	31
Amortization of premium and accretion of discounts on marketable securities	(260)	129
Changes in operating assets and liabilities:
Accounts receivable, related party	79	135
Prepaid expenses and other current assets	(196)	(32)
Other long-term assets	(593)	(652)
Accounts payable and accrued expenses	3,606	471
Accounts payable and accrued expenses, related party	(554)	(167)
Other long-term liabilities	218	165
Net cash used in operating activities	(28,441)	(25,349)
Investing Activities
Purchases of marketable securities	(100,635)	(56,427)
Maturities of marketable securities	77,217	68,605
Net cash (used in) provided by investing activities	(23,418)	12,178
Financing Activities
Proceeds from issuance of common stock, net	53,679
Proceeds from exercise of stock options	232
Payment of fee related to long-term debt	(344)
Proceeds from issuance of long-term debt, net		7,453
Net cash provided by financing activities	53,567	7,453
Net increase (decrease) in cash and cash equivalents	1,708	(5,718)
Cash and cash equivalents at beginning of period	9,725	15,443
Cash and cash equivalents at end of period	11,433	9,725
Supplemental disclosure of cash flow information:
Interest paid	$ 627	352
Supplemental non-cash disclosures:
Warrants issued in connection with debt facility		$ 172

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation 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, and we intend to pair them with molecular or cellular diagnostics to identify respond to We intend to advance our product candidates through a combination of internal development and strategic partnerships and maintain 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., a private Delaware corporation incorporated in the State of Delaware in August 2014, for the periods prior to our reverse merger transaction which took place on March 6, 2015, or the Merger, and Kura Oncology, Inc., a Delaware corporation incorporated in November 2007 and formerly known as Zeta Acquisition Corp. III, for the periods following the Merger.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies 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 our president and chief executive officer, 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. 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 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. 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. 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. While our current and historical operating losses and negative cash flows are indicators of impairment, we believe that future cash flows to be received support the carrying value of our long-lived assets and, accordingly, have not recognized any impairment losses through December 31, 2017. Research and Development Expenses Research and development expenses consist of costs associated with our research activities including salaries, benefits, share-based compensation and other personnel costs, clinical trial costs, preclinical study fees, manufacturing costs for non-commercial products, costs for the development of our earlier-stage programs and research supply, equipment and facility costs. 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, 2017, 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. Awards granted to non-employees are subject to periodic revaluation over their vesting terms. The fair value of non-employee awards is remeasured at each reporting period as the underlying awards vest unless the instruments are fully vested, immediately exercisable and nonforfeitable on the date of grant. We record 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 is recorded on the earlier of the performance commitment date or the date the services required are completed and are remeasured at fair value during the service period. As non-employee restricted stock awards vest, they are remeasured at fair value and expensed based on the intrinsic value method which is 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 Income (Loss) Comprehensive income (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 solely of unrealized gains and losses on marketable securities. 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 share equivalents outstanding for the period determined using the treasury-stock method. Dilutive common stock equivalents are comprised of unvested restricted stock awards, outstanding stock options and outstanding warrants. 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. Because of our net loss, unvested restricted stock awards, outstanding stock options and outstanding warrants are excluded from the calculation of diluted net loss per common share for the years ended December 31, 2017 and 2016, 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 for the years ended December 31, 2017 and 2016, in thousands: Years Ended December 31, 2017 2016 Stock options 2,233 1,202 Unvested restricted stock awards 793 2,020 Warrants 34 68 Total 3,060 3,290

Recent Accounting Pronouncement

Recent Accounting Pronouncements	12 Months Ended
	Dec. 31, 2017
Accounting Changes And Error Corrections [Abstract]
Recent Accounting Pronouncements	3. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers (Topic 606). The guidance provides that an entity recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments, and assets recognized from costs incurred to obtain or fulfill a contract. We adopted this standard on January 1, 2018. We currently do not have any revenue contracts with customers. The adoption of this guidance does not have an impact on our financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires lessees to recognize a right-to-use asset and a lease obligation for all leases. Lessees are permitted to make an accounting policy election to not recognize an asset and liability for leases with a term of 12 months or less. Lessor accounting under the new standard is substantially unchanged. Additional qualitative and quantitative disclosures, including significant judgments made by management, will be required.

Investments

Investments	12 Months Ended
	Dec. 31, 2017
Investments All Other Investments [Abstract]
Investments	4. Investments We invest in available-for-sale securities consisting of money market funds, U.S. Treasury securities, corporate debt securities, commercial paper and government sponsored enterprise securities. Available-for-sale securities are classified as part of either cash and cash equivalents or short-term investments in the balance sheets. The following tables summarize, by major security type, our investments that are measured at fair value on a recurring basis as of December 31, 2017 and 2016, in thousands: As of December 31, 2017 Maturities (years) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds 1 or less $ 5,848 $ — $ — $ 5,848 Commercial paper 1 or less 2,993 — — 2,993 Total cash equivalents 8,841 — — 8,841 Short-term investments: U.S. Treasury securities 2 or less 22,929 — (42 ) 22,887 Commercial paper 1 or less 50,929 — — 50,929 Corporate debt securities 1 or less 7,903 — (7 ) 7,896 Total short-term investments 81,761 — (49 ) 81,712 Total $ 90,602 $ — $ (49 ) $ 90,553 As of December 31, 2016 Maturities (years) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds 1 or less $ 5,762 $ — $ — $ 5,762 Commercial paper 1 or less 2,000 — — 2,000 Total cash equivalents 7,762 — — 7,762 Short-term investments: U.S. Treasury securities 2 or less 28,006 5 (9 ) 28,002 Commercial paper 1 or less 14,273 — — 14,273 Corporate debt securities 2 or less 13,603 — (14 ) 13,589 Government sponsored enterprise securities 1 or less 2,201 — — 2,201 Total short-term investments 58,083 5 (23 ) 58,065 Total $ 65,845 $ 5 $ (23 ) $ 65,827 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, 2017 and 2016, $76.7 million and $50.3 million of our short-term investments had maturities less than one year, respectively, and $5.0 million and $7.8 million had maturities between one to two years, respectively. There were no realized gains or losses for the years ended December 31, 2017 and 2016. As of December 31, 2017 and 2016, $30.8 million and $32.8 million of our marketable securities were in gross unrealized loss positions, respectively, all of which had been in such position for less than 12 months. We reviewed our marketable securities as of December 31, 2017 and determined that the unrealized losses were not considered to be other-than-temporary based upon (i) the financial strength of the issuing institution and (ii) the fact that all securities have been in an unrealized loss position for less than 12 months. In addition, we do not intend to sell these securities and it is not more likely than not that we will be required to sell these securities before the recovery of their amortized cost basis. As such, we did not recognize any such impairment in our financial statements as of December 31, 2017 and 2016.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	5. Fair Value Measurements As of December 31, 2017 and 2016, 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, accrued expenses and all related party amounts approximate their fair values as of December 31, 2017 and 2016, 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, commercial paper and government sponsored enterprise securities, 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. 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 as of December 31, 2017 and 2016, in thousands: As of December 31, 2017 Balance Level 1 Level 2 Cash equivalents: Money market funds $ 5,848 $ 5,848 $ — Commercial paper 2,993 — 2,993 Total cash equivalents 8,841 5,848 2,993 Short-term investments: U.S. Treasury securities 22,887 22,887 — Commercial paper 50,929 — 50,929 Corporate debt securities 7,896 — 7,896 Total short-term investments 81,712 22,887 58,825 Total $ 90,553 $ 28,735 $ 61,818 As of December 31, 2016 Balance Level 1 Level 2 Cash equivalents: Money market funds $ 5,762 $ 5,762 $ — Commercial paper 2,000 — 2,000 Total cash equivalents 7,762 5,762 2,000 Short-term investments: U.S. Treasury securities 28,002 28,002 — Commercial paper 14,273 — 14,273 Corporate debt securities 13,589 — 13,589 Government sponsored enterprise securities 2,201 — 2,201 Total short-term investments 58,065 28,002 30,063 Total $ 65,827 $ 33,764 $ 32,063 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 8, Long-Term Debt, for further discussion of our term loan facility.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Property and Equipment, Net	6. Property and Equipment, Net Property and equipment consisted of the following, in thousands: December 31, 2017 2016 Computer software and equipment $ 92 $ 92 Less: accumulated depreciation (82 ) (52 ) Property and equipment, net $ 10 $ 40 Depreciation expense was $30,000 and $31,000 for the years ended December 31, 2017 and 2016, respectively.

Accounts Payable and Accrued Li

Accounts Payable and Accrued Liabilities	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
Accounts Payable and Accrued Liabilities	7. Accounts Payable and Accrued Liabilities Accounts payable and accrued liabilities consisted of the following, in thousands: December 31, 2017 2016 Accounts payable $ 1,248 $ 638 Accrued compensation and benefits 2,345 1,907 Accrued research and development expenses 3,852 1,669 Other accrued expenses 839 467 Total accounts payable and accrued expenses $ 8,284 $ 4,681

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-Term Debt	8. Long-Term Debt On April 27, 2016, we entered into a loan and security agreement with Oxford Finance LLC and Silicon Valley Bank, or the Lenders, which was amended in May 2017, pursuant to which the Lenders provided a loan facility of up to $20.0 million. The loan and security agreement, as amended, shall be referred to as the Loan Agreement. On April 27, 2016, we borrowed $7.5 million from the Lenders, or Term Loan. We could, at our sole discretion, borrow up to an additional $12.5 million at a certain specified time. On October 31, 2017, the draw period for the additional loan expired without us drawing down the additional loan; therefore, we paid an unused fee of approximately $0.3 million on November 1, 2017. The fee was recorded as a debt discount in the year ended December 31, 2017 and is being amortized to interest expense using the effective interest method through the scheduled maturity date. The Term Loan will mature on November 1, 2020 , or Maturity Date. Repayment of the We are subject to customary affirmative and restrictive covenants under the term loan facility. Our obligations under the 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 Loan Agreement. The Loan Agreement also contains customary indemnification obligations and customary events of default, including, among other things, our failure to fulfill certain obligations under the 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 Lenders’ lien in the collateral or in the value of such collateral. In the event of default by us under the Loan Agreement, the Lenders 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 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, 2017, we were in compliance with all financial covenants under the Loan Agreement and there had been no material adverse change or other events of default that had not subsequently been remediated or waived by the Lenders. In connection with the Term Loan, we issued to the Lenders warrants to purchase up to 67,976 shares of our common stock at an exercise price of $3.31 per share, or the Warrants. The Warrants are exercisable, in whole or in part, and will terminate on the earlier of April 27, 2026 or the closing of certain merger or consolidation transactions. The Warrants were valued using the Black-Scholes model with the following assumptions: volatility of 70.92%, expected term of ten years, risk-free interest rate of 2.11% and a zero dividend yield. The fair value of the Warrants was approximately $0.2 million upon issuance, which was recorded as a debt discount and is being amortized to interest expense using the effective interest method through the scheduled maturity date. In February 2017, Silicon Valley Bank exercised its warrant to purchase 33,988 shares of common stock in a cashless exercise resulting in the issuance of 17,070 shares of our common stock. The warrant issued to Oxford Finance LLC to purchase up to 33,988 shares of our common stock remains outstanding as of December 31, 2017. The following table summarizes future minimum payments under the term loan facility as of December 31, 2017, in thousands: Year Ending December 31, 2018 $ 2,376 2019 3,388 2020 3,435 Total future minimum payments 9,199 Less: interest payments (1,699 ) Principal amount of long-term debt 7,500 Less: Unamortized discount (402 ) Long-term debt, net of unamortized discount 7,098 Current portion of long-term debt (1,531 ) Long-term debt, net $ 5,567

License Agreements

License Agreements	12 Months Ended
	Dec. 31, 2017
License Agreements [Abstract]
License Agreements	9. 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 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. The University of California San Francisco License Agreement In November 2014, we entered into a license agreement with The Regents of the University of California San Francisco, or UCSF, which was amended in April 2015, under which we received certain license rights. The agreement provided for an upfront payment as well as contingent milestone payments. Additionally, pursuant to the terms of the agreement we paid a one-time indexed milestone payment of $0.5 million. The license agreement with UCSF was terminated in January 2017. 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. All milestone payments under the agreements will be recognized as research and development expense upon completion of the required events because the triggering events are not considered to be probable until they are achieved. As of December 31, 2017, we have not achieved any milestones under the 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. Additional payments will be due for each subsequent indication if specified regulatory approvals are achieved. We will recognize the milestones as expense when each event occurs. 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 years ended December 31, 2017 and 2016, we paid to Araxes milestone payments 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 and a $0.1 million milestone payment upon the filing of the investigational new drug application, or IND, for KO-947 in the fourth quarter of 2016.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies Sponsored Research Agreement with the University of Michigan In February 2015, we entered into a sponsored research agreement with the University of Michigan, as amended in May 2017, under which we agreed to sponsor up to $2.1 million of research at the University of Michigan over a three-year period. We received a non-exclusive right to any technology developed under the agreement and had an option right for an exclusive license to invention made under the agreement. The sponsored research agreement expired by its terms in February 2018. Costs incurred for the sponsored research agreement were expensed as incurred. For the years ended December 31, 2017 and 2016, we recorded approximately $0.2 million and $1.0 million, respectively, in research and development expense under this sponsored research agreement. 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. In December 2016, we entered into a new sublease, or the New Sublease, with Wellspring 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 will expire on October 31, 2019. 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. Future minimum payments required under the facility leases as of December 31, 2017 are summarized as follows, in thousands: Year Ending December 31, 2018 $ 461 2019 436 2020 159 Total future minimum lease payments $ 1,056 Rent expense for the years ended December 31, 2017 and was approximately $0.4 million and $0.3 million, respectively. 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.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	11. Stockholders’ Equity 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. In January 2017, we entered into an at-the-market issuance sales agreement with Cowen and Company, LLC, or Cowen, which was amended in November 2017, under which we may offer and sell, from time to time, in our sole discretion, shares of our common stock having an aggregate offering price of up to $100.0 million through Cowen as our sales agent, or the ATM facility. In January 2018, we sold an aggregate of 3,136,722 shares of our common stock under the ATM facility at a weighted-average price per share of $18.85, for gross proceeds of approximately $59.1 million.

Equity Incentive Plan

Equity Incentive Plan	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Plan	12. Equity Incentive Plan As of December 31, 2017, under our Amended and Restated The number of shares available for future grant under our 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, 2018, an automatic increase pursuant to the 2014 Plan occurred, resulting in 1,208,683 additional shares available for future grant under the 2014 Plan. In addition, as of December 31, 2017, we had 238,705 shares of common stock reserved for future issuance under our 2015 Employee Stock Purchase Plan, or ESPP, which has not been implemented as of December 31, 2017. 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 2017, 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, 2017, 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, 2016 1,202 $ 6.38 Granted 1,163 $ 7.07 Exercised (47 ) $ 4.93 Canceled (85 ) $ 6.45 Outstanding at December 31, 2017 2,233 $ 6.77 8.5 $ 19,095 Vested and expected to vest at December 31, 2017 2,233 $ 6.77 8.5 $ 19,095 Exercisable at December 31, 2017 819 $ 6.53 8.1 $ 7,207 The aggregate intrinsic value in the above table is calculated as the difference between the closing price of our common stock at December 31, 2017 of $15.30 per share and the exercise price of stock options that had strike prices below the closing price. For the year ended December 31, 2017, the total intrinsic value of stock options exercised and cash received from stock option exercises were both approximately $0.2 million. There were no option exercises in 2016. The assumptions used to estimate the fair value of stock options granted to employees in the years ended December 31, 2017 and 2016 using the Black-Scholes model were as follows: Years Ended December 31, 2017 2016 Weighted average grant date fair value per share $ 4.76 $ 3.09 Expected volatility 75.4% — 77.7% 73.8% — 76.6% Expected term (in years) 5.50 — 6.08 5.50 — 6.08 Risk free interest rate 1.4% — 2.0% 1.5% — 1.7% Expected dividend yield — — In estimating fair value for stock options issued under the 2014 Plan, expected volatility was based on 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. Pursuant to ASU 2016-09, Improvements to Employee Share-Based Payment Accounting, we apply actual forfeitures as they occur. For the years ended December 31, 2017 and 2016, we recognized $2.3 million and $1.1 million expense related to options, respectively. As of December 31, 2017, unrecognized estimated compensation expense related to options was $5.7 million, which is expected to be recognized over the weighted-average remaining requisite service period of approximately 2.5 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 vest 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 maintain a repurchase right where shares of restricted common stock are released from such repurchase right over a period of time of continued service by the recipient. The repurchase price for unvested stock awards will be 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, 2017, there were 792,765 The following is a summary of restricted stock awards activity for the year ended December 31, 2017, in thousands (except weighted-average grant date fair value data): Number Shares Employee Non-employee Weighted- Average Grant Date Fair Value of Employee Awards Unvested at December 31, 2016 2,020 1,697 323 $ 0.002 Granted — — — $ — Vested (1,193 ) (1,000 ) (193 ) $ 0.002 Canceled (34 ) (34 ) — $ 0.002 Unvested at December 31, 2017 793 663 130 $ 0.002 Vested at December 31, 2017 4,093 3,375 718 $ 0.002 The following table summarizes share-based compensation expense related to restricted stock awards for the years ended December 31, 2017 and 2016, in thousands: Years Ended December 31, 2017 2016 Employee $ 132 $ 133 Non-employee 2,077 858 Total $ 2,209 $ 991 The total fair value of restricted stock awards vested during the years ended December 31, 2017 and 2016 were $12.7 million and $5.3 million, respectively. As of December 31, 2017, unrecognized estimated compensation expense related to employee restricted stock awards was $0.1 million, which is expected to be recognized over the weighted-average remaining requisite service period of approximately 0.7 years. The following table summarizes share-based compensation expense for all share-based compensation arrangements, in thousands: Years Ended December 31, 2017 2016 Research and development $ 3,048 $ 1,293 General and administrative 1,497 796 Total share-based compensation expense $ 4,545 $ 2,089

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	13. Related Party Transactions Our president and chief executive officer is also the sole managing member of Araxes. Four individuals are significant stockholders of each of us and Araxes. The following is a summary of transactions with Araxes for the years ended December 31, 2017 and 2016: • Asset Purchase Agreement Under the asset purchase agreement with Araxes, for the years ended December 31, 2017 and 2016, we paid to Araxes milestone payments of $0.2 million upon dosing of the first patient in the first KO-947 Phase 1 clinical trial in the second quarter of 2017 and $0.1 million to Araxes upon the filing of the IND for KO-947 in the fourth quarter of 2016. • Facility Sublease We sublease office space in San Diego, California from Wellspring. Rent expense, including operating costs, related to the Sublease and the New Sublease, as applicable, for each of the years ended December 31, 2017 and 2016 was approximately $0.2 million and $0.1 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 for office space in San Diego, California. The New Sublease commenced in June 2017 and will expire on October 31, 2019. See Note 10, 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 a fixed fee of $65,000 per month for management services. 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 $350,000, 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, 2017 and 2016, we recorded reimbursements of approximately $0.3 million and $0.4 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, 2017 and 2016, approximately $0.2 million and $0.3 million related to management fees and reimbursements of research and development services, respectively, 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, 2017 and 2016, we recognized approximately $1.2 million and $4.0 million, respectively, from research and development services provided to us under this agreement as research and development expense, related party on the statements of operations and comprehensive loss. As of December 31, 2017 and 2016, approximately $0.2 million and $0.7 million, respectively, related to research and development services under this agreement are included in accounts payable and accrued expenses, related party on the balance sheets.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2017
Postemployment Benefits [Abstract]
Employee Benefit Plan	14. 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. Beginning in 2016, 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, 2017 and 2016, we incurred approximately $0.2 million in expenses in each year related to the safe harbor contribution.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	15. Income Taxes We file tax returns as prescribed by the tax laws of the jurisdictions in which we operate. In the normal course of business, our 2014 Our effective income tax rate differs from the statutory federal rate of 34% for the years ended December 31, 2017 and 2016, due to the following, in thousands: Years Ended December 31, 2017 2016 Income taxes at statutory federal rate $ (12,048 ) $ (9,370 ) State income tax, net of federal benefit (2,226 ) (1,823 ) Share-based compensation 1,046 564 Research and development tax credits (476 ) (398 ) Other (209 ) (112 ) Impact of Tax Act 9,517 — Valuation allowance 4,396 11,139 Income tax expense $ — $ — Significant components of our deferred tax assets at December 31, 2017 and 2016 are shown below, in thousands: December 31, 2017 2016 Deferred tax assets Net operating loss carryforwards $ 22,050 $ 18,321 Research and development tax credit carryforwards 1,690 971 Intangibles 708 982 Accruals 692 809 Share-based compensation 601 267 Other 110 104 Total deferred tax assets 25,851 21,454 Less valuation allowance (25,851 ) (21,454 ) Net deferred tax assets $ — $ — Public Law No. 115-97 known as t he Tax Cut and Jobs Act, or the Tax Act, was enacted on December 22, 2017. and interpretation and examination of the tax legislation evolves. At December 31, 2017, we had federal and state net operating loss, or NOL, carryforwa rds of $75.4 million and $90.9 million, respe begin to expire in 2034, unless previously utilized. We have $90.4 million of state losses that begin to expire in 2034 and $0.5 million of state loss carryforwards that begin to expire in 2030, unless previously utilized. We also have federal and state research and development credit carryforwards of $1.4 million (net of $0.5 million to be utilized as a payroll tax offset) and $1.0 million, respectively research and development expire in 2034, unless previously research and development research and development 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. The valuation allowance increased by $4.4 million and $11.1 million from December 31, 2016 to 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 an additional study and concluded no further ownership changes occurred through December 31, 2017. 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, 2017 2016 Gross unrecognized tax benefits at the beginning of the year $ 358 $ 167 Increases related to prior year tax positions 42 — Increases from tax positions taken in the current year 215 191 Gross unrecognized tax benefits at the end of the year $ 615 $ 358 Our practice is to recognize interest and penalties related to income tax matters in income tax expense. We did 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.

Summary of Significant Accoun22

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Use of Estimates	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	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by our president and chief executive officer, 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.
Cash and Cash Equivalents	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 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 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 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	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.
Property and Equipment	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.
Impairment of Long-Lived Assets	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. While our current and historical operating losses and negative cash flows are indicators of impairment, we believe that future cash flows to be received support the carrying value of our long-lived assets and, accordingly, have not recognized any impairment losses through December 31, 2017.
Research and Development Expenses	Research and Development Expenses Research and development expenses consist of costs associated with our research activities including salaries, benefits, share-based compensation and other personnel costs, clinical trial costs, preclinical study fees, manufacturing costs for non-commercial products, costs for the development of our earlier-stage programs and research supply, equipment and facility costs. 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, 2017, we have no in-licensed technologies that have alternative future uses in research and development projects or otherwise.
Clinical Trial Costs and Accruals	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	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	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. Awards granted to non-employees are subject to periodic revaluation over their vesting terms. The fair value of non-employee awards is remeasured at each reporting period as the underlying awards vest unless the instruments are fully vested, immediately exercisable and nonforfeitable on the date of grant. We record 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 is recorded on the earlier of the performance commitment date or the date the services required are completed and are remeasured at fair value during the service period. As non-employee restricted stock awards vest, they are remeasured at fair value and expensed based on the intrinsic value method which is 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 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 Income (Loss)	Comprehensive Income (Loss) Comprehensive income (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 solely of unrealized gains and losses on marketable securities.
Net Loss per Share	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 share equivalents outstanding for the period determined using the treasury-stock method. Dilutive common stock equivalents are comprised of unvested restricted stock awards, outstanding stock options and outstanding warrants. 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. Because of our net loss, unvested restricted stock awards, outstanding stock options and outstanding warrants are excluded from the calculation of diluted net loss per common share for the years ended December 31, 2017 and 2016, 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 for the years ended December 31, 2017 and 2016, in thousands: Years Ended December 31, 2017 2016 Stock options 2,233 1,202 Unvested restricted stock awards 793 2,020 Warrants 34 68 Total 3,060 3,290
Recent Accounting Pronouncements	In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers (Topic 606). The guidance provides that an entity recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments, and assets recognized from costs incurred to obtain or fulfill a contract. We adopted this standard on January 1, 2018. We currently do not have any revenue contracts with customers. The adoption of this guidance does not have an impact on our financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires lessees to recognize a right-to-use asset and a lease obligation for all leases. Lessees are permitted to make an accounting policy election to not recognize an asset and liability for leases with a term of 12 months or less. Lessor accounting under the new standard is substantially unchanged. Additional qualitative and quantitative disclosures, including significant judgments made by management, will be required.

Summary of Significant Accoun23

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
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 for the years ended December 31, 2017 and 2016, in thousands: Years Ended December 31, 2017 2016 Stock options 2,233 1,202 Unvested restricted stock awards 793 2,020 Warrants 34 68 Total 3,060 3,290

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2017
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 as of December 31, 2017 and 2016, in thousands: As of December 31, 2017 Maturities (years) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds 1 or less $ 5,848 $ — $ — $ 5,848 Commercial paper 1 or less 2,993 — — 2,993 Total cash equivalents 8,841 — — 8,841 Short-term investments: U.S. Treasury securities 2 or less 22,929 — (42 ) 22,887 Commercial paper 1 or less 50,929 — — 50,929 Corporate debt securities 1 or less 7,903 — (7 ) 7,896 Total short-term investments 81,761 — (49 ) 81,712 Total $ 90,602 $ — $ (49 ) $ 90,553 As of December 31, 2016 Maturities (years) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds 1 or less $ 5,762 $ — $ — $ 5,762 Commercial paper 1 or less 2,000 — — 2,000 Total cash equivalents 7,762 — — 7,762 Short-term investments: U.S. Treasury securities 2 or less 28,006 5 (9 ) 28,002 Commercial paper 1 or less 14,273 — — 14,273 Corporate debt securities 2 or less 13,603 — (14 ) 13,589 Government sponsored enterprise securities 1 or less 2,201 — — 2,201 Total short-term investments 58,083 5 (23 ) 58,065 Total $ 65,845 $ 5 $ (23 ) $ 65,827

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
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 as of December 31, 2017 and 2016, in thousands: As of December 31, 2017 Balance Level 1 Level 2 Cash equivalents: Money market funds $ 5,848 $ 5,848 $ — Commercial paper 2,993 — 2,993 Total cash equivalents 8,841 5,848 2,993 Short-term investments: U.S. Treasury securities 22,887 22,887 — Commercial paper 50,929 — 50,929 Corporate debt securities 7,896 — 7,896 Total short-term investments 81,712 22,887 58,825 Total $ 90,553 $ 28,735 $ 61,818 As of December 31, 2016 Balance Level 1 Level 2 Cash equivalents: Money market funds $ 5,762 $ 5,762 $ — Commercial paper 2,000 — 2,000 Total cash equivalents 7,762 5,762 2,000 Short-term investments: U.S. Treasury securities 28,002 28,002 — Commercial paper 14,273 — 14,273 Corporate debt securities 13,589 — 13,589 Government sponsored enterprise securities 2,201 — 2,201 Total short-term investments 58,065 28,002 30,063 Total $ 65,827 $ 33,764 $ 32,063

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Property and Equipment, Net	Property and equipment consisted of the following, in thousands: December 31, 2017 2016 Computer software and equipment $ 92 $ 92 Less: accumulated depreciation (82 ) (52 ) Property and equipment, net $ 10 $ 40

Accounts Payable and Accrued 27

Accounts Payable and Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
Accounts Payable and Accrued Liabilities	Accounts payable and accrued liabilities consisted of the following, in thousands: December 31, 2017 2016 Accounts payable $ 1,248 $ 638 Accrued compensation and benefits 2,345 1,907 Accrued research and development expenses 3,852 1,669 Other accrued expenses 839 467 Total accounts payable and accrued expenses $ 8,284 $ 4,681

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
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, 2017, in thousands: Year Ending December 31, 2018 $ 2,376 2019 3,388 2020 3,435 Total future minimum payments 9,199 Less: interest payments (1,699 ) Principal amount of long-term debt 7,500 Less: Unamortized discount (402 ) Long-term debt, net of unamortized discount 7,098 Current portion of long-term debt (1,531 ) Long-term debt, net $ 5,567

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Future Minimum Payments Required under Facility Leases	Future minimum payments required under the facility leases as of December 31, 2017 are summarized as follows, in thousands: Year Ending December 31, 2018 $ 461 2019 436 2020 159 Total future minimum lease payments $ 1,056

Equity Incentive Plan (Tables)

Equity Incentive Plan (Tables)	12 Months Ended
	Dec. 31, 2017
Summary of Stock Option Activities	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, 2017, 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, 2016 1,202 $ 6.38 Granted 1,163 $ 7.07 Exercised (47 ) $ 4.93 Canceled (85 ) $ 6.45 Outstanding at December 31, 2017 2,233 $ 6.77 8.5 $ 19,095 Vested and expected to vest at December 31, 2017 2,233 $ 6.77 8.5 $ 19,095 Exercisable at December 31, 2017 819 $ 6.53 8.1 $ 7,207
Summary of Assumptions used to Estimate the Fair Value of Stock Options Under Black-Scholes Model	The assumptions used to estimate the fair value of stock options granted to employees in the years ended December 31, 2017 and 2016 using the Black-Scholes model were as follows: Years Ended December 31, 2017 2016 Weighted average grant date fair value per share $ 4.76 $ 3.09 Expected volatility 75.4% — 77.7% 73.8% — 76.6% Expected term (in years) 5.50 — 6.08 5.50 — 6.08 Risk free interest rate 1.4% — 2.0% 1.5% — 1.7% Expected dividend yield — —
Summary of Restricted Stock Awards Activity	The following is a summary of restricted stock awards activity for the year ended December 31, 2017, in thousands (except weighted-average grant date fair value data): Number Shares Employee Non-employee Weighted- Average Grant Date Fair Value of Employee Awards Unvested at December 31, 2016 2,020 1,697 323 $ 0.002 Granted — — — $ — Vested (1,193 ) (1,000 ) (193 ) $ 0.002 Canceled (34 ) (34 ) — $ 0.002 Unvested at December 31, 2017 793 663 130 $ 0.002 Vested at December 31, 2017 4,093 3,375 718 $ 0.002
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, 2017 2016 Research and development $ 3,048 $ 1,293 General and administrative 1,497 796 Total share-based compensation expense $ 4,545 $ 2,089
Restricted Stock Awards
Summary of Share-based Compensation Expense	The following table summarizes share-based compensation expense related to restricted stock awards for the years ended December 31, 2017 and 2016, in thousands: Years Ended December 31, 2017 2016 Employee $ 132 $ 133 Non-employee 2,077 858 Total $ 2,209 $ 991

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation	Our effective income tax rate differs from the statutory federal rate of 34% for the years ended December 31, 2017 and 2016, due to the following, in thousands: Years Ended December 31, 2017 2016 Income taxes at statutory federal rate $ (12,048 ) $ (9,370 ) State income tax, net of federal benefit (2,226 ) (1,823 ) Share-based compensation 1,046 564 Research and development tax credits (476 ) (398 ) Other (209 ) (112 ) Impact of Tax Act 9,517 — Valuation allowance 4,396 11,139 Income tax expense $ — $ —
Components of Deferred Tax Assets	Significant components of our deferred tax assets at December 31, 2017 and 2016 are shown below, in thousands: December 31, 2017 2016 Deferred tax assets Net operating loss carryforwards $ 22,050 $ 18,321 Research and development tax credit carryforwards 1,690 971 Intangibles 708 982 Accruals 692 809 Share-based compensation 601 267 Other 110 104 Total deferred tax assets 25,851 21,454 Less valuation allowance (25,851 ) (21,454 ) 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, 2017 2016 Gross unrecognized tax benefits at the beginning of the year $ 358 $ 167 Increases related to prior year tax positions 42 — Increases from tax positions taken in the current year 215 191 Gross unrecognized tax benefits at the end of the year $ 615 $ 358

Summary of Significant Accoun32

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017USD ($)Segment
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment	1
Impairment losses on long-lived assets | $	$ 0
Computer Software and Equipment
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	3 years

Summary of Significant Accoun33

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, 2017	Dec. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	3,060	3,290
Unvested Restricted Stock Awards
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	793	2,020
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	2,233	1,202
Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities	34	68

Investments - Investments Measu

Investments - Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Short-term investments	$ 81,712	$ 58,065
Fair Value Measurements on Recurring Basis
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, Amortized Cost	8,841	7,762
Cash equivalents, Fair Value	8,841	7,762
Short-term investments, Amortized Cost	81,761	58,083
Short-term investments, Unrealized Gains		5
Short-term investments, Unrealized Losses	(49)	(23)
Short-term investments	81,712	58,065
Cash equivalents and Short-term investments, Amortized Cost	90,602	65,845
Cash equivalents and Short-term investments, Fair Value	$ 90,553	$ 65,827
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	$ 5,848	$ 5,762
Cash equivalents, Fair Value	$ 5,848	$ 5,762
Fair Value Measurements on Recurring Basis | Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	1 or less	1 or less
Cash equivalents, Amortized Cost	$ 2,993	$ 2,000
Cash equivalents, Fair Value	2,993	2,000
Short-term investments, Amortized Cost	50,929	14,273
Short-term investments	$ 50,929	$ 14,273
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	$ 22,929	$ 28,006
Short-term investments, Unrealized Gains		5
Short-term investments, Unrealized Losses	(42)	(9)
Short-term investments	$ 22,887	$ 28,002
Fair Value Measurements on Recurring Basis | Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	1 or less	2 or less
Short-term investments, Amortized Cost	$ 7,903	$ 13,603
Short-term investments, Unrealized Losses	(7)	(14)
Short-term investments	$ 7,896	$ 13,589
Fair Value Measurements on Recurring Basis | Government Sponsored Enterprise Securities
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)		1 or less
Short-term investments, Amortized Cost		$ 2,201
Short-term investments		$ 2,201

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Investments All Other Investments [Abstract]
Short-term investments with maturities less than one year	$ 76,700,000	$ 50,300,000
Short-term investments with maturities between one to two years	5,000,000	7,800,000
Available-for-sale securities, realized gains or losses	0	0
Marketable securities gross unrealized loss positions for less than twelve months	$ 30,800,000	$ 32,800,000

Fair Value Measurements - Fair

Fair Value Measurements - Fair Values of Investment Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 81,712	$ 58,065
Fair Value Measurements on Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	8,841	7,762
Short-term investments	81,712	58,065
Cash equivalents and short-term investments	90,553	65,827
Fair Value Measurements on Recurring Basis | Government Sponsored Enterprise Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		2,201
Fair Value Measurements on Recurring Basis | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	5,848	5,762
Short-term investments	22,887	28,002
Cash equivalents and short-term investments	28,735	33,764
Fair Value Measurements on Recurring Basis | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	2,993	2,000
Short-term investments	58,825	30,063
Cash equivalents and short-term investments	61,818	32,063
Fair Value Measurements on Recurring Basis | Level 2 | Government Sponsored Enterprise Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		2,201
Fair Value Measurements on Recurring Basis | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	5,848	5,762
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	5,848	5,762
Fair Value Measurements on Recurring Basis | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	2,993	2,000
Short-term investments	50,929	14,273
Fair Value Measurements on Recurring Basis | Commercial Paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	2,993	2,000
Short-term investments	50,929	14,273
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	22,887	28,002
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	22,887	28,002
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	7,896	13,589
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	$ 7,896	$ 13,589

Property and Equipment, Net (De

Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Less: accumulated depreciation	$ (82)	$ (52)
Property and equipment, net	10	40
Computer Software and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 92	$ 92

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Depreciation expense	$ 30	$ 31

Accounts Payable and Accrued 39

Accounts Payable and Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accounts payable	$ 1,248	$ 638
Accrued compensation and benefits	2,345	1,907
Accrued research and development expenses	3,852	1,669
Other accrued expenses	839	467
Total accounts payable and accrued expenses	$ 8,284	$ 4,681

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Detail) - USD ($)	Nov. 01, 2017	Apr. 27, 2016	Aug. 31, 2017	Feb. 28, 2017	Dec. 31, 2017	May 31, 2017
Debt Instrument [Line Items]
Maximum borrowing capacity under term loans						$ 20,000,000
Credit facility, unused fee	$ 300,000
Principal amount outstanding on loan					$ 7,500,000
Term loan unused facility		$ 12,500,000
Additional borrowing description					We could, at our sole discretion, borrow up to an additional $12.5 million at a certain specified time. On October 31, 2017, the draw period for the additional loan expired without us drawing down the additional loan; therefore, we paid an unused fee of approximately $0.3 million on November 1, 2017. The unused fee was recorded as a debt discount in the year ended December 31, 2017 and is being amortized to interest expense using the effective interest method through the scheduled maturity date.
Common stock, shares issued			8,805,000
Silicon Valley Bank
Debt Instrument [Line Items]
Warrants issued to purchase of common stock				33,988
Common stock, shares issued				17,070
Maximum [Member] | Oxford Finance LLC
Debt Instrument [Line Items]
Warrants issued to purchase of common stock					33,988
Term Loan
Debt Instrument [Line Items]
Principal amount outstanding on loan		$ 7,500,000
Term loan facility maturity date		Nov. 1, 2020
Description of term loan payment terms					The Term Loan will mature on November 1, 2020, or Maturity Date. Repayment of the Term Loan is interest only through May 1, 2018, followed by 30 equal monthly payments of principal plus accrued interest commencing on June 1, 2018.
Percentage of prime rate included in effective interest rate		4.25%
Final payment as a percentage of amounts borrowed		7.50%
Final payment due on the maturity date		$ 600,000
Team loan effective interest rate description					The per annum interest rate for the Term Loan is the greater of (i) 7.75% and (ii) the sum of (a) the prime rate reported in The Wall Street Journal on the last business day of the month that immediately precedes the month in which the interest will accrue, plus (b) 4.25%.
Fair Value Of Warrants		$ 200,000
Term Loan | Term Loan Warrants
Debt Instrument [Line Items]
Warrants exercisable exercise price		$ 3.31
Warrants termination date					Apr. 27, 2026
Volatility Rate		70.92%
Expected Term		10 years
Risk Free Interest Rate		2.11%
Dividend yield		0.00%
Term Loan | Maximum [Member] | Term Loan Warrants
Debt Instrument [Line Items]
Warrants issued to purchase of common stock		67,976
Term Loan | Base Rate | Minimum
Debt Instrument [Line Items]
Minimum percentage of interest rate on borrowings		7.75%
Term Loan | Transaction Occurring Assumption One
Debt Instrument [Line Items]
Prepayment fee equal to outstanding principal amount		1.00%
Term Loan | Transaction Occurring Assumption Two
Debt Instrument [Line Items]
Prepayment fee equal to outstanding principal amount		2.00%

Long-Term Debt - Future Minimum

Long-Term Debt - Future Minimum Payments under Term Loan Facility (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
2,018	$ 2,376
2,019	3,388
2,020	3,435
Total future minimum payments	9,199
Less: interest payments	(1,699)
Principal amount outstanding on loan	7,500
Less: Unamortized discount	(402)
Long-term debt, net of unamortized discount	7,098
Current portion of long-term debt	(1,531)
Long-term debt, net	$ 5,567	$ 7,324

License Agreements - Additional

License Agreements - Additional Information (Detail) - USD ($) $ in Millions	Dec. 23, 2014	Dec. 22, 2014	Dec. 18, 2014	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2017
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties		$ 80
Araxes Asset Purchase Agreement
License Agreements [Line Items]
Convertible notes payable, related party	$ 0.5
Contingent Milestone Payables	9.7
Milestone payment paid				$ 0.2	$ 0.1
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
The University of California San Francisco License Agreement
License Agreements [Line Items]
Indexed milestone paid						$ 0.5
License agreement termination description.						The license agreement with UCSF was terminated in January 2017.
Janssen License Agreement
License Agreements [Line Items]
Agreement termination written notice			180 days
Agreement termination notice period in event of material breach			45 days
Initiation of Certain Development Activities
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties		$ 0.5
Specified Regulatory Approvals
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties		28.7
Specified Levels of Product Sales
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties		$ 50.8
Certain Regulatory Filings and Approvals | Araxes Asset Purchase Agreement
License Agreements [Line Items]
Contingent Milestone Payables	1.2
Initiation of Certain Development Activities | Araxes Asset Purchase Agreement
License Agreements [Line Items]
Total future milestone payments under license agreements with related party	$ 8.5
Up front Payment Arrangement | Janssen License Agreement
License Agreements [Line Items]
Upfront license fee			$ 1

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	May 31, 2017USD ($)	Aug. 01, 2015USD ($)ft²	Dec. 31, 2016USD ($)ft²	Aug. 31, 2014USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)ft²
Loss Contingencies [Line Items]
Rent expense					$ 400,000	$ 300,000
Cambridge, Massachusetts
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. 1, 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
Wellspring Biosciences Inc | La Jolla, California
Loss Contingencies [Line Items]
Percentage of rent escalation				3.00%
Sublease expiration date						Oct. 31, 2019
Sublease term description						In December 2016, we entered into a third amendment to Sublease pursuant to which the Sublease expired in June 2017
Wellspring Biosciences Inc | La Jolla, California | Monthly
Loss Contingencies [Line Items]
Rent expense				$ 4,820
Wellspring Biosciences Inc | San Diego, California
Loss Contingencies [Line Items]
Percentage of rent escalation			3.00%			3.00%
Sublease expiration date					Oct. 31, 2019	Oct. 31, 2019
Sublease term description						The terms of the New Sublease commenced in June 2017
Operating lease, area of space | ft²			5,216			5,216
Security deposit			$ 16,000			$ 16,000
Wellspring Biosciences Inc | San Diego, California | Monthly
Loss Contingencies [Line Items]
Rent expense			$ 16,000
The University of Michigan Sponsored Research Agreement
Loss Contingencies [Line Items]
Sponsor of research over three- year	$ 2,100,000
Sponsored research agreement period	3 years
Research and development					$ 200,000	$ 1,000,000

Commitments and Contingencies44

Commitments and Contingencies - Future Minimum Payments Required under Facility Leases (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Leases [Abstract]
2,018	$ 461
2,019	436
2,020	159
Total future minimum lease payments	$ 1,056

Stockholder's Equity - Addition

Stockholder's Equity - Additional Information (Detail) - USD ($)	Nov. 30, 2017	Jan. 31, 2018	Aug. 31, 2017	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Common stock, shares issued			8,805,000
Common stock, issued price per share			$ 6.50
Proceeds from issuance of common stock, net			$ 53,500,000	$ 53,679,000
At-The-Market Facility | Subsequent Event
Stockholders' Equity Note [Abstract]
Common stock, shares issued		3,136,722
Common stock weighted average price per share		$ 18.85
Proceeds from issuance of common stock, gross		$ 59,100,000
Cowen and Company, LLC | At-The-Market Facility | Maximum [Member]
Stockholders' Equity Note [Abstract]
Aggregate offering price	$ 100,000,000

Equity Incentive Plan - Additio

Equity Incentive Plan - Additional Information (Detail) - USD ($)	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Cash received from stock options exercised		$ 232,000
Share-based compensation expense		$ 4,545,000	$ 2,089,000
Number of shares, subject to repurchase		792,765	2,020,000
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Closing price of common stock		$ 15.30
Total intrinsic value of stock option exercised		$ 200,000	$ 0
Cash received from stock options exercised		200,000
Share-based compensation expense		2,300,000	1,100,000
Unrecognized estimated stock option compensation expenses		$ 5,700,000
Weighted average service period		2 years 6 months
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense		$ 2,209,000	991,000
Weighted average service period		8 months 12 days
Number of shares, subject to repurchase		663,180
Fair value of awards vested		$ 12,700,000	$ 5,300,000
Unrecognized Expense		$ 100,000
Non Employee Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, subject to repurchase		129,585
Maximum [Member] | 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
Minimum | Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		3 years
2014 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common shares reserved for future issuance pursuant to future option grants		518,868
Percentage of increase in common shares reserved for future issuance pursuant to future option grants		4.00%
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 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance		7,684,531
2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common shares reserved for future issuance pursuant to future option grants		238,705
2015 Employee Stock Purchase Plan | Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional common shares reserved for future issuance pursuant to future option grants		2,000,000
2015 Employee Stock Purchase Plan | Maximum [Member] | Employee Stock Option
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%
Subsequent Event | 2014 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional common shares reserved for future issuance pursuant to future option grants	1,208,683

Equity Incentive Plan - Summary

Equity Incentive Plan - Summary of Stock Option Activities (Detail) - Stock Option $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options Outstanding, Beginning Balance, Number of Shares | shares	1,202
Granted, Number of Shares | shares	1,163
Exercised, Number of Shares | shares	(47)
Canceled, Number of Shares | shares	(85)
Stock Options Outstanding, Ending Balance, Number of Shares | shares	2,233
Vested and expected to vest, Number of Shares | shares	2,233
Exercisable, Number of Shares | shares	819
Outstanding, Beginning Balance, Weighted-Average Exercise Price per Share | $ / shares	$ 6.38
Granted, Weighted-Average Exercise Price per Share | $ / shares	7.07
Exercised, Weighted-Average Exercise Price per Share | $ / shares	4.93
Canceled, Weighted-Average Exercise Price per Share | $ / shares	6.45
Outstanding, Ending Balance, Weighted-Average Exercise Price per Share | $ / shares	6.77
Vested and expected to vest, Weighted-Average Exercise Price per Share | $ / shares	6.77
Exercisable, Weighted-Average Exercise Price per Share | $ / shares	$ 6.53
Outstanding, Weighted-Average Remaining Contractual Term (years)	8 years 6 months
Vested and expected to vest, Weighted-Average Remaining Contractual Term (years)	8 years 6 months
Exercisable, Weighted-Average Remaining Contractual Term (years)	8 years 1 month 6 days
Outstanding, Aggregate Intrinsic Value | $	$ 19,095
Vested and expected to vest, Aggregate Intrinsic Value | $	19,095
Exercisable, Aggregate Intrinsic Value | $	$ 7,207

Equity Incentive Plan - Summa48

Equity Incentive Plan - Summary of Assumptions used to Estimate the Fair Value of Stock Options Under Black-Scholes Model (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value per share	$ 4.76	$ 3.09
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	75.40%	73.80%
Expected term (in years)	5 years 6 months	5 years 6 months
Risk free interest rate	1.40%	1.50%
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	77.70%	76.60%
Expected term (in years)	6 years 29 days	6 years 29 days
Risk free interest rate	2.00%	1.70%

Equity Incentive Plan - Summa49

Equity Incentive Plan - Summary of Restricted Stock Awards Activity (Detail) - Restricted Stock Awards shares in Thousands	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Beginning Balance, Number of Shares	2,020
Vested, Number of Shares	(1,193)
Canceled, Number of Shares	(34)
Ending Balance, Number of Shares	793
Vested, Number of Shares	4,093
Beginning Balance, Weighted-Average Grant Date Fair Value | $ / shares	$ 0.002
Vested, Weighted-Average Grant Date Fair Value | $ / shares	0.002
Canceled, Weighted-Average Grant Date Fair Value | $ / shares	0.002
Ending Balance, Weighted-Average Grant Date Fair Value | $ / shares	0.002
Vested, Weighted-Average Grant Date Fair Value | $ / shares	$ 0.002
Employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Beginning Balance, Number of Shares	1,697
Vested, Number of Shares	(1,000)
Canceled, Number of Shares	(34)
Ending Balance, Number of Shares	663
Vested, Number of Shares	3,375
Non-employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Beginning Balance, Number of Shares	323
Vested, Number of Shares	(193)
Ending Balance, Number of Shares	130
Vested, Number of Shares	718

Equity Incentive Plan - Summa50

Equity Incentive Plan - Summary of Share-based Compensation Expense Related to Restricted Stock Awards Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total	$ 4,545	$ 2,089
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Employee	132	133
Non-employee	2,077	858
Total	$ 2,209	$ 991

Equity Incentive Plan - Summa51

Equity Incentive Plan - Summary of Share-based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 4,545	$ 2,089
Research and development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	3,048	1,293
General and administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 1,497	$ 796

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($)	Apr. 30, 2016	Oct. 01, 2014	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Accounts receivable, related party				$ 295,000	$ 216,000	$ 295,000
Research and development, related party					1,312,000	3,829,000
Accounts payable and accrued expenses, related party				770,000	$ 216,000	770,000
Araxes Pharma LLC | Management Fees
Related Party Transaction [Line Items]
Management Fee, Description					We have a management services agreement with Araxes pursuant to which Araxes pays us a fixed fee of $65,000 per month for management services.
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 $350,000, 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 service agreement, fixed	$ 65,000
Service Agreement for research and development	$ 350,000
Agreement expiration date		Dec. 31, 2015
Agreement termination notice period		30 days
Amount received on research and development services					$ 300,000	400,000
Accounts receivable, related party				300,000	$ 200,000	300,000
Wellspring Biosciences Inc | Service Agreements
Related Party Transaction [Line Items]
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.
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, related party					$ 1,200,000	4,000,000
Accounts payable and accrued expenses, related party				700,000	200,000	700,000
Wellspring Biosciences Inc | Sublease
Related Party Transaction [Line Items]
Rent expense related to office space sublease					$ 200,000	$ 100,000
Sublease agreement description					In December 2016, we entered into a third amendment to Sublease pursuant to which the Sublease expired in June 2017.
Wellspring Biosciences Inc | San Diego California
Related Party Transaction [Line Items]
Sublease commencement date					Jun. 30, 2017
Sublease expiration date					Oct. 31, 2019	Oct. 31, 2019
Araxes Asset Purchase Agreement | Araxes Pharma LLC
Related Party Transaction [Line Items]
Milestone payment paid			$ 200,000	$ 100,000

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Detail) - Safe Harbor 401(k) Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Expenses related to contribution plan	$ 0.2	$ 0.2
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Percent of employees compensation	3.00%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Effective federal statutory income tax rate, Percent		34.00%	34.00%
Remeasurement of net deferred tax balance reduction		$ 9,517,000
Loss carryforwards begin to expire		2,034
Increase in valuation allowance		$ 4,400,000	$ 11,100,000
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
Maximum [Member]
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Effective federal statutory income tax rate, Percent		35.00%
Scenario Forecast
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Effective federal statutory income tax rate, Percent	21.00%
Domestic Tax Authority
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards		$ 75,400,000
Research and development credit carryforwards		1,400,000
Research and development credit carryforwards, payroll tax offset utilized		$ 500,000
Credit carry forward begin to expire		2,034
Domestic Tax Authority | Research and Development Credits
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Research and development credit carryforwards payroll tax offset qualifying amount		$ 300,000
Deferred tax assets tax credit carryforwards recognized benefit		300,000	$ 300,000
State and Local Jurisdiction
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards		90,900,000
Research and development credit carryforwards		1,000,000
State and Local Jurisdiction | Research and Development Credits
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Credit carryforwards not subject to expiration		900,000
State and Local Jurisdiction | Expire in 2034
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards		$ 90,400,000
Credit carry forward begin to expire		2,034
State and Local Jurisdiction | Expire in 2030
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards		$ 500,000
Credit carry forward begin to expire		2,030
State and Local Jurisdiction | Expire in 2031 | Research and Development Credits
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Credit carry forward begin to expire		2,031
Credit carryforwards subject to expiration		$ 100,000

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income taxes at statutory federal rate	$ (12,048)	$ (9,370)
State income tax, net of federal benefit	(2,226)	(1,823)
Share-based compensation	1,046	564
Research and development tax credits	(476)	(398)
Other	(209)	(112)
Impact of Tax Act	9,517
Valuation allowance	4,396	11,139
Income tax expense	$ 0	$ 0

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Net operating loss carryforwards	$ 22,050	$ 18,321
Research and development tax credit carryforwards	1,690	971
Intangibles	708	982
Accruals	692	809
Share-based compensation	601	267
Other	110	104
Total deferred tax assets	25,851	21,454
Less valuation allowance	(25,851)	(21,454)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Schedule of Acti

Income Taxes - Schedule of Activity Related to Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Gross unrecognized tax benefits at the beginning of the year	$ 358	$ 167
Increases related to prior year tax positions	42
Increases from tax positions taken in the current year	215	191
Gross unrecognized tax benefits at the end of the year	$ 615	$ 358