Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2015

Summary of Stock Option Activity

Stock option activity is summarized as follows:

	Number of Outstanding Options			Weighted Average Price		Weighted Remaining Contractual Term		Aggregate Intrinsic Value (in 000s)
Outstanding as of December 31, 2014		1,514,471		$	4.60
Granted		1,715,028		$	11.29
Exercised		(197,253	)	$	2.78
Canceled		(406,966	)	$	6.37
Outstanding as of December 31, 2015		2,625,280		$	8.83		8.02	$	6,684
Options vested and expected to vest as of December 31, 2015		2,625,280		$	8.83		8.02	$	6,684
Options exercisable as of December 31, 2015		899,931		$	4.91		6.64	$	5,063

Summary of Assumptions Used to Determine Fair Value of Employee Stock Purchase Plan

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the ESPP offering were as follows:

	Year Ended
	December 31, 2015
Expected term (in years)		0.50
Risk-free interest rate		0.33	%
Expected volatility		67.3	%
Expected dividend yield		0.0	%

Schedule of Allocation of Stock-Based Compensation for All Options Including Performance Options with Market Condition

The allocation of stock-based compensation for all options, including performance options,with market condition is as follows (in thousands):

	Years Ended December 31,
	2015		2014		2013
Research and development	$	2,524	$	527	$	96
General and administrative		2,332		1,264		59
	$	4,856	$	1,791	$	155

Summary of Warrants Outstanding

Warrants outstanding as of December 31, 2015:

Number		Exercise Price		Expiration
Outstanding		Per Share		Date
	9,051	$	6.63	September 2017
	2,006	$	7.48	March 2021
	14,913	$	20.12	July 2023
	25,970

Summary of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance is as follows:

	As of December 31,
	2015		2014
Conversion of redeemable convertible preferred stock		—		9,238,868
Conversion of redeemable convertible preferred stock issuable    upon conversion of promissory note		—		94,455
Redeemable convertible preferred stock warrants		—		25,970
Common stock warrants		25,970		—
Common stock options outstanding		2,625,280		1,514,471
Shares available under the 2014 Plan		984,357		180,190
Shares available under the 2015 Plan		903,350		—
Shares available under the 2015 ESPP Plan		227,623		—
		4,766,580		11,053,954

Employee Stock Option [Member]

Summary of Assumptions Used to Determine Fair Value of Employee Stock Option Grants and Performance Options with Market Condition

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows:

	Years Ended December 31,
	2015			2014			2013
Expected term (in years)	5.50 – 6.08			5.77 – 6.56			6.52 – 6.56
Risk-free interest rate	1.5% – 1.9%			1.7% – 2.7%			2.0% – 2.2%
Expected volatility	79.2% – 100.9%				111.0	%		109.0	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

Performance Options with Market Condition [Member]

Summary of Assumptions Used to Determine Fair Value of Employee Stock Option Grants and Performance Options with Market Condition

The assumptions used to determine the fair value of the performance options with market condition were as follows:

	Year Ended December 31, 2015
Expected term (in years)		4.8
Risk-free interest rate		2.05	%
Expected volatility		80.6	%
Expected dividend yield		0.0	%