View Filing Data

108,227

81,712

Prepaid expenses and other current assets

230

216

2,420

1,280

Total current assets

128,535

94,641

Property and equipment, net

Other long-term assets

1,091

1,200

Total assets

129,627

95,851

Current liabilities:

Accounts payable and accrued expenses

9,330

8,284

Accounts payable and accrued expenses, related party

437

216

Current portion of long-term debt, net

2,813

1,531

Total current liabilities

12,580

10,031

Long-term debt, net

4,150

5,567

Other long-term liabilities

500

388

Total liabilities

17,230

15,986

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; 33,375 and 30,217 shares issued as of June 30, 2018 and December 31, 2017, respectively; and 33,173 and 29,424 shares outstanding as of June 30, 2018 and December 31, 2017, respectively; excluding 202 and 793 shares subject to repurchase as of June 30, 2018 and December 31, 2017, respectively

Additional paid-in capital

231,120

169,201

Accumulated other comprehensive loss

(93)

(49)

Accumulated deficit

(118,633)

(89,290)

Total stockholders' equity

112,397

79,865

Total liabilities and stockholders' equity

$ 129,627

$ 95,851

[1]	The balance sheet data at December 31, 2017 has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by U.S. generally accepted accounting principles for complete financial statements.

Condensed Balance Sheets (Unaudited) (Parenthetical) - $ / shares

Jun. 30, 2018

Dec. 31, 2017

^[1]

Statement Of Financial Position [Abstract]

Preferred stock, par value

$ 0.0001

Preferred stock, shares authorized

10,000,000

Preferred stock, shares issued

Preferred stock, shares outstanding

Common stock, par value

$ 0.0001

Common stock, shares authorized

200,000,000

Common stock, shares issued

33,375,000

30,217,000

Common stock, shares outstanding

33,173,000

29,424,000

Number of shares, subject to repurchase

202,000

793,000

[1]	The balance sheet data at December 31, 2017 has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by U.S. generally accepted accounting principles for complete financial statements.

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating Expenses:
Research and development	$ 11,099	$ 5,158	$ 22,366	$ 10,378
Research and development, related party	377	494	676	787
General and administrative	3,736	2,217	7,102	4,292
General and administrative, related party	64	61	123	126
Total operating expenses	15,276	7,930	30,267	15,583
Other Income (Expense):
Management fee income, related party	180	195	375	390
Interest income	624	124	1,074	252
Interest expense	(267)	(209)	(525)	(412)
Total other income	537	110	924	230
Net Loss	$ (14,739)	$ (7,820)	$ (29,343)	$ (15,353)
Net loss per share, basic and diluted	$ (0.45)	$ (0.40)	$ (0.91)	$ (0.78)
Weighted average number of shares used in computing net loss per share, basic and diluted	32,971	19,789	32,403	19,627
Comprehensive Loss:
Net Loss	$ (14,739)	$ (7,820)	$ (29,343)	$ (15,353)
Other comprehensive loss	(25)	(3)	(44)	(4)
Comprehensive Loss	$ (14,764)	$ (7,823)	$ (29,387)	$ (15,357)

Condensed Statements of Cash Flows (Unaudited) - USD ($)
$ in Thousands

6 Months Ended

Jun. 30, 2018

Jun. 30, 2017

Operating Activities

Net loss

$ (29,343)

$ (15,353)

Adjustments to reconcile net loss to net cash used in operating activities:

Share-based compensation expense

4,415

1,924

Non-cash interest expense

114

Depreciation expense

Amortization of premium and accretion of discounts on marketable securities

(703)

Changes in operating assets and liabilities:

Prepaid expenses and other current assets

(14)

(9)

(1,026)

(462)

Other long-term assets

(42)

(117)

Accounts payable and accrued expenses

814

(502)

Accounts payable and accrued expenses, related party

221

(373)

Other long-term liabilities

112

109

Net cash used in operating activities

(25,443)

(14,732)

Investing Activities

Purchases of marketable securities

(106,850)

(19,360)

Maturities of marketable securities

80,993

36,327

Net cash (used in) provided by investing activities

(25,857)

16,967

Financing Activities

Proceeds from issuance of common stock, net

57,650

159

Proceeds from exercise of stock options

125

Repayment of long-term debt

(250)

Net cash provided by financing activities

57,525

194

Net increase in cash and cash equivalents

6,225

2,429

Cash and cash equivalents at beginning of period

11,433

^[1]

9,725

Cash and cash equivalents at end of period

$ 17,658

$ 12,154

[1]	The balance sheet data at December 31, 2017 has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by U.S. generally accepted accounting principles for complete financial statements.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Comprehensive Loss

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

Net Loss per Share

Net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common shares and common 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 periods presented, due to the anti-dilutive effect of the securities.

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

	Three and Six Months Ended
	2018		2017
Stock options		3,097		2,214
Unvested restricted stock awards		202		1,387
Warrants		34		34
Total		3,333		3,635

Recent Accounting Pronouncements

In February 2016, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2016-02, Leases (Topic 842), which requires lessees to recognize a right-to-use asset and a lease obligation for all leases. Additional qualitative and quantitative disclosures, including significant judgments made by management, will be required. ASU 2016-02 is required to be adopted at the earliest period presented using a modified retrospective approach. In July 2018, the FASB issued ASU 2018-11 to provide another transition method for adoption of the new lease standard by recognizing a cumulative-effect adjustment to the opening balance sheet of retained earnings in the period of adoption. We plan to adopt the lease standard using this alternative transition method on January 1, 2019 and will evaluate existing leases and recognize a right-to-use asset and lease obligation for all leases with terms greater than 12 months on our condensed financial statements. We are currently evaluating the effect the new lease standard will have on our condensed financial statements and related disclosures.

Investments

6 Months Ended

Jun. 30, 2018

Investments All Other Investments [Abstract]

Investments

3. Investments

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

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

		As of June 30, 2018
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	1 or less	$	11,317	$	—	$	—		$	11,317
Commercial paper	1 or less		3,997		—		—			3,997
Total cash equivalents			15,314		—		—			15,314

Short-term investments:
U.S. Treasury securities	2 or less		49,620		1		(85	)		49,536
Commercial paper	1 or less		47,281		—		—			47,281
Corporate debt securities	1 or less		11,424		—		(14	)		11,410
Total short-term investments			108,325		1		(99	)		108,227
Total		$	123,639	$	1	$	(99	)	$	123,541

		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

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 June 30, 2018, $93.4 million of our short-term investments had maturities less than one year, and $14.8 million had maturities between one to two years. There were no realized gains or losses for the three and six months ended June 30, 2018. As of June 30, 2018, $51.0 million of our marketable securities were in gross unrealized loss positions, all of which had been in such position for less than 12 months. We reviewed our marketable securities as of June 30, 2018 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 of June 30, 2018, we did not recognize any such impairment in our condensed financial statements.

Fair Value Measurements

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

4. Fair Value Measurements

As a basis for considering assumptions that market participants would use in pricing an asset or liability, 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; and

•	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.

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

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

	As of June 30, 2018
	Balance		Level 1		Level 2
Cash equivalents:
Money market funds	$	11,317	$	11,317	$	—
Commercial paper		3,997	—			3,997
Total cash equivalents		15,314		11,317		3,997

Short-term investments:
U.S. Treasury securities		49,536		49,536	—
Commercial paper		47,281	—			47,281
Corporate debt securities		11,410	—			11,410
Total short-term investments		108,227		49,536		58,691
Total	$	123,541	$	60,853	$	62,688

	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

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.

Equity Incentive Plan

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Equity Incentive Plan

7. Equity Incentive Plan

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development	$	1,369	$	678	$	2,808	$	1,266
General and administrative		867		352		1,607		658
Total share-based compensation expense	$	2,236	$	1,030	$	4,415	$	1,924

Restricted stock awards:
Employee	$	33	$	33	$	66	$	66
Nonemployee		798		445		1,799		828
Total	$	831	$	478	$	1,865	$	894

Stock options:
Employee	$	1,349	$	530	$	2,429	$	989
Nonemployee		50		22		115		41
Total	$	1,399	$	552	$	2,544	$	1,030

Employee stock purchase plan:
Employee	$	6	$	—	$	6	$	—
Total	$	6	$	—	$	6	$	—

Pursuant to our 2015 Employee Stock Purchase Plan, we commenced the first purchase period in the second quarter of 2018. As of June 30, 2018, unrecognized compensation costs related to employee stock options and restricted stock awards were approximately $15.6 million and $0.1 million, respectively, which are expected to be recognized over a weighted average period of approximately 2.7 years and 0.2 years, respectively.

Related Party Transactions

6 Months Ended

Jun. 30, 2018

Related Party Transactions

8. Related Party Transactions

Our president and chief executive officer is also the sole managing member of Araxes Pharma LLC, or Araxes, and is a significant stockholder of each of us and Araxes. The following is a summary of transactions with Araxes for the three and six months ended June 30, 2018 and 2017:

•

Asset Purchase Agreement

Under our asset purchase agreement with Araxes, in the three and six months ended June 30, 2017, we paid a milestone payment of $0.2 million to Araxes following dosing of the first patient in the first KO-947 Phase 1 clinical trial in April 2017.

•

Facility Sublease

We subleased office space in La Jolla, California from Wellspring Biosciences, Inc., or Wellspring, a wholly owned subsidiary of Araxes pursuant to a sublease agreement that expired in June 2017. In December 2016, we entered into a new sublease agreement with Wellspring for office space in San Diego, California, or New Sublease. The New Sublease will expire on October 31, 2019. For both the three months ended June 30, 2018 and 2017, rent expense, including operating costs, related to our subleases was approximately $0.1 million. For the six months ended June 30, 2018 and 2017, rent expense, including operating costs, related to our subleases was approximately $0.2 million and $0.1 million, respectively.

•

Management Fees

Effective April 2018, we amended our management services agreement with Araxes. Under the amendment, Araxes pays us a fixed fee of $60,000 per month for management services, which is reduced from the fixed fee of $65,000 per month. 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 $367,000, plus actual expenses as reasonably incurred. The initial term of this agreement expired on December 31, 2015 but, pursuant to the terms of the agreement, renews automatically for additional consecutive one-year periods. The agreement may be terminated by either party with a notice of at least 30 days prior to the expiration of the then-renewal term. For the three months ended June 30, 2018 and 2017, we recorded reimbursements of approximately $0.1 million in each period, and for the six months ended June 30, 2018 and 2017, we recorded reimbursements of approximately $0.1 million and $0.2 million, respectively, for research and development services provided to Araxes, which was recorded as a reduction to research and development expenses on our condensed statements of operations and comprehensive loss. As of June 30, 2018 and December 31, 2017, approximately $0.2 million related to management fees and reimbursements of research and development services are included in accounts receivable, related party on our condensed 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 three months ended June 30, 2018 and 2017, we recognized approximately $0.4 million and $0.3 million, respectively, and for both the six months ended June 30, 2018 and 2017, we recognized $0.7 million from research and development services provided to us under this agreement as research and development expense, related party on our condensed statements of operations and comprehensive loss. As of June 30, 2018 and December 31, 2017, approximately $0.4 million and $0.2 million, respectively, related to research and development services under this agreement are included in accounts payable and accrued expenses, related party on our condensed balance sheets.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Comprehensive Loss

Net Loss per Share

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

	Three and Six Months Ended
	2018		2017
Stock options		3,097		2,214
Unvested restricted stock awards		202		1,387
Warrants		34		34
Total		3,333		3,635

Recent Accounting Pronouncements

Investments (Tables)

6 Months Ended

Jun. 30, 2018

Investments All Other Investments [Abstract]

Investments Measured at Fair Value on Recurring Basis

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

		As of June 30, 2018
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	1 or less	$	11,317	$	—	$	—		$	11,317
Commercial paper	1 or less		3,997		—		—			3,997
Total cash equivalents			15,314		—		—			15,314

Short-term investments:
U.S. Treasury securities	2 or less		49,620		1		(85	)		49,536
Commercial paper	1 or less		47,281		—		—			47,281
Corporate debt securities	1 or less		11,424		—		(14	)		11,410
Total short-term investments			108,325		1		(99	)		108,227
Total		$	123,639	$	1	$	(99	)	$	123,541

		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

Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Schedule Of Fair Value Measurements, By Major Security Type

	As of June 30, 2018
	Balance		Level 1		Level 2
Cash equivalents:
Money market funds	$	11,317	$	11,317	$	—
Commercial paper		3,997	—			3,997
Total cash equivalents		15,314		11,317		3,997

Short-term investments:
U.S. Treasury securities		49,536		49,536	—
Commercial paper		47,281	—			47,281
Corporate debt securities		11,410	—			11,410
Total short-term investments		108,227		49,536		58,691
Total	$	123,541	$	60,853	$	62,688

	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

Equity Incentive Plan (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Share-based Compensation Expense

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development	$	1,369	$	678	$	2,808	$	1,266
General and administrative		867		352		1,607		658
Total share-based compensation expense	$	2,236	$	1,030	$	4,415	$	1,924

Restricted stock awards:
Employee	$	33	$	33	$	66	$	66
Nonemployee		798		445		1,799		828
Total	$	831	$	478	$	1,865	$	894

Stock options:
Employee	$	1,349	$	530	$	2,429	$	989
Nonemployee		50		22		115		41
Total	$	1,399	$	552	$	2,544	$	1,030

Employee stock purchase plan:
Employee	$	6	$	—	$	6	$	—
Total	$	6	$	—	$	6	$	—

Investments - Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands

6 Months Ended

12 Months Ended

Jun. 30, 2018

Dec. 31, 2017

Schedule Of Available For Sale Securities [Line Items]

Fair Value Measurements on Recurring Basis

$ 108,227

$ 81,712

^[1]

Schedule Of Available For Sale Securities [Line Items]

Cash equivalents, Amortized Cost

15,314

8,841

Cash equivalents, Fair Value

15,314

8,841

Short-term investments, Unrealized Gains

108,325

81,761

Short-term investments, Unrealized Losses

(99)

(49)

Cash equivalents and Short-term investments, Amortized Cost

108,227

81,712

123,639

90,602

Cash equivalents and Short-term investments, Fair Value

$ 123,541

$ 90,553

Fair Value Measurements on Recurring Basis | Money Market Funds

Schedule Of Available For Sale Securities [Line Items]

Cash equivalents, Amortized Cost

1 or less

$ 11,317

$ 5,848

Cash equivalents, Fair Value

$ 11,317

$ 5,848

Fair Value Measurements on Recurring Basis | Commercial Paper

Schedule Of Available For Sale Securities [Line Items]

Cash equivalents, Amortized Cost

1 or less

$ 3,997

$ 2,993

Cash equivalents, Fair Value

$ 3,997

$ 2,993

1 or less

$ 47,281

$ 50,929

Fair Value Measurements on Recurring Basis | U.S. Treasury Securities

$ 47,281

$ 50,929

Schedule Of Available For Sale Securities [Line Items]

2 or less

Short-term investments, Unrealized Gains

$ 49,620

$ 22,929

Short-term investments, Unrealized Losses

(85)

(42)

Fair Value Measurements on Recurring Basis | Corporate Debt Securities

$ 49,536

$ 22,887

Schedule Of Available For Sale Securities [Line Items]

1 or less

Short-term investments, Unrealized Losses

$ 11,424

$ 7,903

(14)

(7)

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

$ 11,410

$ 7,896

[1]	The balance sheet data at December 31, 2017 has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by U.S. generally accepted accounting principles for complete financial statements.

Fair Value Measurements - Fair Values of Investment Securities (Detail) - USD ($)
$ in Thousands

Jun. 30, 2018

Dec. 31, 2017

Fair Value Measurements on Recurring Basis

$ 108,227

$ 81,712

^[1]

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

15,314

8,841

Cash equivalents and short-term investments

108,227

81,712

123,541

90,553

Fair Value Measurements on Recurring Basis | Level 1

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

11,317

5,848

Cash equivalents and short-term investments

49,536

22,887

60,853

28,735

Fair Value Measurements on Recurring Basis | Level 2

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

3,997

2,993

Cash equivalents and short-term investments

58,691

58,825

62,688

61,818

Fair Value Measurements on Recurring Basis | Money Market Funds

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

Fair Value Measurements on Recurring Basis | Money Market Funds | Level 1

11,317

5,848

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

Fair Value Measurements on Recurring Basis | Commercial Paper

11,317

5,848

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

3,997

2,993

Fair Value Measurements on Recurring Basis | Commercial Paper | Level 2

47,281

50,929

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

3,997

2,993

Fair Value Measurements on Recurring Basis | U.S. Treasury Securities

47,281

50,929

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

Fair Value Measurements on Recurring Basis | U.S. Treasury Securities | Level 1

49,536

22,887

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

Fair Value Measurements on Recurring Basis | Corporate Debt Securities

49,536

22,887

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

Fair Value Measurements on Recurring Basis | Corporate Debt Securities | Level 2

11,410

7,896

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

Accrued research and development expenses

$ 11,410

$ 7,896

[1]	The balance sheet data at December 31, 2017 has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by U.S. generally accepted accounting principles for complete financial statements.

Accounts Payable and Accrued Liabilities (Detail) - USD ($)
$ in Thousands

Jun. 30, 2018

Dec. 31, 2017

Payables And Accruals [Abstract]

Accounts payable

$ 1,755

$ 1,248

5,242

3,852

Accrued compensation and benefits

1,563

2,345

Other accrued expenses

770

839

Total accounts payable and accrued expenses

$ 9,330

$ 8,284

^[1]

[1]	The balance sheet data at December 31, 2017 has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by U.S. generally accepted accounting principles for complete financial statements.

Equity Incentive Plan - Summary of Share-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 2,236	$ 1,030	$ 4,415	$ 1,924
Research and development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	1,369	678	2,808	1,266
General and administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	867	352	1,607	658
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	831	478	1,865	894
Employee	33	33	66	66
Nonemployee	798	445	1,799	828
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	1,399	552	2,544	1,030
Nonemployee	50	22	115	41
Employee	1,349	$ 530	2,429	$ 989
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	6		6
Employee	$ 6		$ 6

Related Party Transactions - Additional Information (Detail) - USD ($)

1 Months Ended

3 Months Ended

6 Months Ended

Apr. 30, 2016

Oct. 01, 2014

Apr. 30, 2018

Jun. 30, 2018

Jun. 30, 2017

Jun. 30, 2018

Jun. 30, 2017

Dec. 31, 2017

Research and development, related party

$ 230,000

$ 216,000

^[1]

377,000

$ 494,000

676,000

$ 787,000

Accounts payable and accrued expenses, related party

437,000

$ 437,000

216,000

^[1]

Araxes Pharma LLC

Asset purchase agreement milstone payment

200,000

Araxes Pharma LLC | Management Fees | Management Service

Management Fee, Description

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 $367,000, 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.

Service Agreement for research and development, FTE rate

$ 367,000

Agreement expiration date

Dec. 31, 2015

Agreement termination notice period

30 days

Amount received on research and development services

100,000

$ 100,000

200,000