View Filing Data

166,855

81,712

^[1]

Prepaid expenses and other current assets

232

216

^[1]

2,737

1,280

^[1]

Total current assets

190,392

94,641

^[1]

Property and equipment, net

^[1]

Other long-term assets

1,108

1,200

^[1]

Total assets

191,500

95,851

^[1]

Current liabilities:

Accounts payable and accrued expenses

9,817

8,284

^[1]

Accounts payable and accrued expenses, related party

254

216

^[1]

Current portion of long-term debt, net

2,834

1,531

^[1]

Total current liabilities

12,905

10,031

^[1]

Long-term debt, net

3,432

5,567

^[1]

Other long-term liabilities

556

388

^[1]

Total liabilities

16,893

15,986

^[1]

Stockholders' equity:

Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares issued and outstanding

^[1]

Common stock, $0.0001 par value; 200,000 shares authorized; 38,017 and 30,217 shares issued as of September 30, 2018 and December 31, 2017, respectively; and 38,014 and 29,424 shares outstanding as of September 30, 2018 and December 31, 2017, respectively; excluding 3 and 793 shares subject to repurchase as of September 30, 2018 and December 31, 2017, respectively

^[1]

Additional paid-in capital

308,366

169,201

^[1]

Accumulated other comprehensive loss

(123)

(49)

^[1]

Accumulated deficit

(133,640)

(89,290)

^[1]

Total stockholders' equity

174,607

79,865

^[1]

Total liabilities and stockholders' equity

$ 191,500

$ 95,851

^[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.

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

Sep. 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

38,017,000

30,217,000

Common stock, shares outstanding

38,014,000

29,424,000

Number of shares, subject to repurchase

3,000

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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Expenses:
Research and development	$ 11,480	$ 6,808	$ 33,846	$ 17,186
Research and development, related party	181	334	857	1,121
General and administrative	4,251	2,313	11,353	6,605
General and administrative, related party	70	44	193	170
Total operating expenses	15,982	9,499	46,249	25,082
Other Income (Expense):
Management fee income, related party	180	195	555	585
Interest income	1,047	197	2,121	449
Interest expense	(252)	(226)	(777)	(638)
Total other income	975	166	1,899	396
Net Loss	$ (15,007)	$ (9,333)	$ (44,350)	$ (24,686)
Net loss per share, basic and diluted	$ (0.40)	$ (0.38)	$ (1.30)	$ (1.16)
Weighted average number of shares used in computing net loss per share, basic and diluted	37,789	24,344	34,218	21,217
Comprehensive Loss:
Net Loss	$ (15,007)	$ (9,333)	$ (44,350)	$ (24,686)
Other comprehensive income (loss)	(30)	8	(74)	4
Comprehensive Loss	$ (15,037)	$ (9,325)	$ (44,424)	$ (24,682)

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

9 Months Ended

Sep. 30, 2018

Sep. 30, 2017

Operating Activities

Net loss

$ (44,350)

$ (24,686)

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

Share-based compensation expense

6,938

3,099

Non-cash interest expense

167

Depreciation expense

Amortization of premium and accretion of discounts on marketable securities

(1,299)

(73)

Changes in operating assets and liabilities:

Prepaid expenses and other current assets

(16)

(1,282)

(184)

Other long-term assets

(355)

(205)

Accounts payable and accrued expenses

1,537

1,173

Accounts payable and accrued expenses, related party

(428)

Other long-term liabilities

168

166

Net cash used in operating activities

(38,444)

(20,967)

Investing Activities

Purchases of marketable securities

(203,461)

(79,254)

Maturities of marketable securities

119,543

59,927

Net cash used in investing activities

(83,918)

(19,327)

Financing Activities

Proceeds from issuance of common stock, net

132,170

53,683

Proceeds from exercise of stock options

327

222

Repayment of long-term debt

(1,000)

Net cash provided by financing activities

131,497

53,905

Net increase in cash and cash equivalents

9,135

13,611

Cash and cash equivalents at beginning of period

11,433

^[1]

9,725

Cash and cash equivalents at end of period

$ 20,568

$ 23,336

[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

9 Months Ended

Sep. 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, outstanding warrants and employee stock purchase plan rights.

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, outstanding warrants and employee stock purchase plan rights 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 Nine Months Ended
	September 30,
	2018		2017
Stock options		3,302		2,171
Unvested restricted stock awards		3		1,091
Warrants		34		34
Employee stock purchase plan rights		4		—
Total		3,343		3,296

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. We are in the process of evaluating existing leases and the effect the new lease standard will have on our unaudited condensed financial statements and related disclosure and will recognize a right-to-use asset and lease obligation for all leases with terms greater than 12 months on our unaudited condensed financial statements.

Investments

9 Months Ended

Sep. 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 unaudited condensed balance sheets.

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

		As of September 30, 2018
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	1 or less	$	9,482	$	—	$	—		$	9,482
Commercial paper	1 or less		4,998		—		—			4,998
Total cash equivalents			14,480		—		—			14,480

Short-term investments:
Commercial paper	1 or less		64,415		—		—			64,415
Corporate debt securities	2 or less		52,843		—		(25	)		52,818
U.S. Treasury securities	1 or less		49,722		—		(100	)		49,622
Total short-term investments			166,980		—		(125	)		166,855
Total		$	181,460	$	—	$	(125	)	$	181,335

		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:
Commercial paper	1 or less		50,929		—		—			50,929
Corporate debt securities	1 or less		7,903		—		(7	)		7,896
U.S. Treasury securities	2 or less		22,929		—		(42	)		22,887
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 September 30, 2018, $161.9 million of our short-term investments had maturities less than one year, and $5.0 million had maturities between one to two years. There were no realized gains or losses for the three and nine months ended September 30, 2018. As of September 30, 2018, $102.4 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 September 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 September 30, 2018, we did not recognize any such impairment in our unaudited condensed financial statements.

Fair Value Measurements

9 Months Ended

Sep. 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 September 30, 2018
	Balance		Level 1		Level 2
Cash equivalents:
Money market funds	$	9,482	$	9,482	$	—
Commercial paper		4,998	—			4,998
Total cash equivalents		14,480		9,482		4,998

Short-term investments:
Commercial paper		64,415		—		64,415
Corporate debt securities		52,818	—			52,818
U.S. Treasury securities		49,622		49,622		—
Total short-term investments		166,855		49,622		117,233
Total	$	181,335	$	59,104	$	122,231

	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:
Commercial paper		50,929		—		50,929
Corporate debt securities		7,896		—		7,896
U.S. Treasury securities		22,887		22,887		—
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

9 Months Ended

Sep. 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				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Research and development	$	1,227	$	770	$	4,035	$	2,036
General and administrative		1,296		405		2,903		1,063
Total share-based compensation expense	$	2,523	$	1,175	$	6,938	$	3,099

Restricted stock awards:
Employee	$	29	$	33	$	95	$	99
Nonemployee		823		514		2,623		1,342
Total	$	852	$	547	$	2,718	$	1,441

Stock options:
Employee	$	1,571	$	576	$	4,000	$	1,566
Nonemployee		87		52		201		92
Total	$	1,658	$	628	$	4,201	$	1,658

Employee stock purchase plan:
Employee	$	13	$	—	$	19	$	—
Total	$	13	$	—	$	19	$	—

Pursuant to our 2015 Employee Stock Purchase Plan, we commenced the first purchase period in the second quarter of 2018. As of September 30, 2018, unrecognized compensation costs related to employee stock options was approximately $18.0 million, which is expected to be recognized over a weighted average period of approximately 2.8 years. As of September 30, 2018, there was no remaining unrecognized compensation costs related to employee restricted stock awards.

Related Party Transactions

9 Months Ended

Sep. 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 nine months ended September 30, 2018 and 2017:

•

Asset Purchase Agreement

Under our asset purchase agreement with Araxes, in the nine months ended September 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 September 30, 2018 and 2017, rent expense, including operating costs, related to our subleases was approximately $0.1 million. For the nine months ended September 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 September 30, 2018 and 2017, we recorded reimbursements of approximately $0.1 million in each period, and for the nine months ended September 30, 2018 and 2017, we recorded reimbursements of approximately $0.2 million and $0.3 million, respectively, for research and development services provided to Araxes, which was recorded as a reduction to research and development expenses on our unaudited condensed statements of operations and comprehensive loss. As of September 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 unaudited 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 September 30, 2018 and 2017, we recognized approximately $0.2 million and $0.3 million, respectively, and for the nine months ended September 30, 2018 and 2017, we recognized approximately $0.9 million and $1.0 million, respectively, from research and development services provided to us under this agreement as research and development expense, related party on our unaudited condensed statements of operations and comprehensive loss. As of September 30, 2018 and December 31, 2017, approximately $0.2 million in both periods related to research and development services under this agreement are included in accounts payable and accrued expenses, related party on our unaudited condensed balance sheets.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 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 Nine Months Ended
	September 30,
	2018		2017
Stock options		3,302		2,171
Unvested restricted stock awards		3		1,091
Warrants		34		34
Employee stock purchase plan rights		4		—
Total		3,343		3,296

Recent Accounting Pronouncements

Investments (Tables)

9 Months Ended

Sep. 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 September 30, 2018
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Cash equivalents:
Money market funds	1 or less	$	9,482	$	—	$	—		$	9,482
Commercial paper	1 or less		4,998		—		—			4,998
Total cash equivalents			14,480		—		—			14,480

Short-term investments:
Commercial paper	1 or less		64,415		—		—			64,415
Corporate debt securities	2 or less		52,843		—		(25	)		52,818
U.S. Treasury securities	1 or less		49,722		—		(100	)		49,622
Total short-term investments			166,980		—		(125	)		166,855
Total		$	181,460	$	—	$	(125	)	$	181,335

		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:
Commercial paper	1 or less		50,929		—		—			50,929
Corporate debt securities	1 or less		7,903		—		(7	)		7,896
U.S. Treasury securities	2 or less		22,929		—		(42	)		22,887
Total short-term investments			81,761		—		(49	)		81,712
Total		$	90,602	$	—	$	(49	)	$	90,553

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Schedule Of Fair Value Measurements, By Major Security Type

	As of September 30, 2018
	Balance		Level 1		Level 2
Cash equivalents:
Money market funds	$	9,482	$	9,482	$	—
Commercial paper		4,998	—			4,998
Total cash equivalents		14,480		9,482		4,998

Short-term investments:
Commercial paper		64,415		—		64,415
Corporate debt securities		52,818	—			52,818
U.S. Treasury securities		49,622		49,622		—
Total short-term investments		166,855		49,622		117,233
Total	$	181,335	$	59,104	$	122,231

	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:
Commercial paper		50,929		—		50,929
Corporate debt securities		7,896		—		7,896
U.S. Treasury securities		22,887		22,887		—
Total short-term investments		81,712		22,887		58,825
Total	$	90,553	$	28,735	$	61,818

Equity Incentive Plan (Tables)

9 Months Ended

Sep. 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				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Research and development	$	1,227	$	770	$	4,035	$	2,036
General and administrative		1,296		405		2,903		1,063
Total share-based compensation expense	$	2,523	$	1,175	$	6,938	$	3,099

Restricted stock awards:
Employee	$	29	$	33	$	95	$	99
Nonemployee		823		514		2,623		1,342
Total	$	852	$	547	$	2,718	$	1,441

Stock options:
Employee	$	1,571	$	576	$	4,000	$	1,566
Nonemployee		87		52		201		92
Total	$	1,658	$	628	$	4,201	$	1,658

Employee stock purchase plan:
Employee	$	13	$	—	$	19	$	—
Total	$	13	$	—	$	19	$	—

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

9 Months Ended

12 Months Ended

Sep. 30, 2018

Dec. 31, 2017

Schedule Of Available For Sale Securities [Line Items]

Fair Value Measurements on Recurring Basis

$ 166,855

$ 81,712

^[1]

Schedule Of Available For Sale Securities [Line Items]

Cash equivalents, Amortized Cost

14,480

8,841

Cash equivalents, Fair Value

14,480

8,841

Short-term investments, Unrealized Losses

166,980

81,761

(125)

(49)

Cash equivalents and Short-term investments, Amortized Cost

166,855

81,712

181,460

90,602

Cash equivalents and Short-term investments, Fair Value

$ 181,335

$ 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

$ 9,482

$ 5,848

Cash equivalents, Fair Value

$ 9,482

$ 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

$ 4,998

$ 2,993

Cash equivalents, Fair Value

$ 4,998

$ 2,993

1 or less

$ 64,415

$ 50,929

Fair Value Measurements on Recurring Basis | Corporate Debt Securities

$ 64,415

$ 50,929

Schedule Of Available For Sale Securities [Line Items]

2 or less

1 or less

Short-term investments, Unrealized Losses

$ 52,843

$ 7,903

(25)

(7)

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

$ 52,818

$ 7,896

Schedule Of Available For Sale Securities [Line Items]

1 or less

2 or less

Short-term investments, Unrealized Losses

$ 49,722

$ 22,929

(100)

(42)

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

$ 49,622

$ 22,887

[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

Sep. 30, 2018

Dec. 31, 2017

Fair Value Measurements on Recurring Basis

$ 166,855

$ 81,712

^[1]

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

14,480

8,841

Cash equivalents and short-term investments

166,855

81,712

181,335

90,553

Fair Value Measurements on Recurring Basis | Level 1

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

9,482

5,848

Cash equivalents and short-term investments

49,622

22,887

59,104

28,735

Fair Value Measurements on Recurring Basis | Level 2

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

4,998

2,993

Cash equivalents and short-term investments

117,233

58,825

122,231

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

9,482

5,848

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

Fair Value Measurements on Recurring Basis | Commercial Paper

9,482

5,848

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

4,998

2,993

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

64,415

50,929

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

4,998

2,993

Fair Value Measurements on Recurring Basis | Corporate Debt Securities

64,415

50,929

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

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

52,818

7,896

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

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

52,818

7,896

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

49,622

22,887

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

Accrued research and development expenses

$ 49,622

$ 22,887

[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

Sep. 30, 2018

Dec. 31, 2017

Payables And Accruals [Abstract]

Accounts payable

$ 1,838

$ 1,248

5,312

3,852

Accrued compensation and benefits

2,080

2,345

Other accrued expenses

587

839

Total accounts payable and accrued expenses

$ 9,817

$ 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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 2,523	$ 1,175	$ 6,938	$ 3,099
Research and development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	1,227	770	4,035	2,036
General and administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	1,296	405	2,903	1,063
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	852	547	2,718	1,441
Employee	29	33	95	99
Nonemployee	823	514	2,623	1,342
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	1,658	628	4,201	1,658
Nonemployee	87	52	201	92
Employee	1,571	$ 576	4,000	$ 1,566
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	13		19
Employee	$ 13		$ 19

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

1 Months Ended

3 Months Ended

9 Months Ended

Apr. 30, 2016

Oct. 01, 2014

Apr. 30, 2018

Sep. 30, 2018

Sep. 30, 2017

Sep. 30, 2018

Sep. 30, 2017

Dec. 31, 2017

Research and development, related party

$ 232,000

$ 216,000

^[1]

181,000

$ 334,000

857,000

$ 1,121,000

Accounts payable and accrued expenses, related party

254,000

$ 254,000

216,000

^[1]

Araxes Pharma LLC

Asset purchase agreement milestone 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

$ 200,000

300,000