Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2017

Stock-Based Compensation

Schedule of total employee, director and non-employee stock-based compensation expense recognized

Total employee, director and non-employee stock-based compensation expense recognized for the three months ended March 31, 2017 are as follows (in thousands):

	Three Months Ended
	March 31,
	2017		2016
General and administrative	$	1,467	$	952
Research and development		1,691		1,008
	$	3,158	$	1,960

Schedule of weighted average assumptions used for estimation of fair value of stock options

	Options
	Three Months Ended
	March 31,
	2017		2016
Expected term (years)	6.2		6.1
Expected volatility	89.2	%	75.8	%
Risk-free interest rate	2.07	%	1.56	%
Expected dividend yield	—	%	—	%

Schedule of weighted average assumptions used for estimation of fair value of ESPP

	ESPP
	Three Months Ended
	March 31,
	2017		2016
Expected term (years)	0.5 - 2.0		0.5 - 2.0
Expected volatility	67.8 - 79.8	%	67.8	%
Risk-free interest rate	.55 - .93	%	.55 - .93	%
Expected dividend yield	—	%	—	%

Summary of stock option activity

		Weighted		Weighted
		Average		Average
	Number of	Exercise		Remaining		Aggregate
	Shares subject	Price		Contractual		Intrinsic
	to outstanding	(Per		Term		Value
	options	Share)		(in years)		(in thousands)
Balances at December 31, 2016	4,045,801	$	11.95		7.82
Options granted	1,135,600	$	22.67
Options forfeited	(72,678)	$	15.40
Options exercised	(121,469)	$	8.45
Balance at March 31, 2017	4,987,254	$	14.43		8.05	$	47,683
Exercisable	2,072,560	$	9.61		6.70	$	29,654