Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 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 and six months ended June 30, 2017 are as follows (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2017		2016		2017		2016
General and administrative	$	1,416	$	874	$	2,884	$	1,826
Research and development		2,032		1,159		3,723		2,167
	$	3,448	$	2,033	$	6,607	$	3,993

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	1,356,100	$	22.65
Options forfeited	(76,606)	$	15.60
Options exercised	(252,278)	$	6.66
Balance at June 30, 2017	5,073,017	$	15.02		7.92	$	33,950
Exercisable	2,206,587	$	10.22		6.60	$	24,051

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

	Options				Options
	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2017		2016		2017		2016
Expected term (years)	6.1		5.9		6.1		6.1
Expected volatility	88.9	%	76.1	%	89.2	%	75.8	%
Risk-free interest rate	1.91	%	1.36	%	2.04	%	1.53	%
Expected dividend yield	—	%	—	%	—	%	—	%

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

	ESPP				ESPP
	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2017		2016		2017		2016
Expected term (years)	0.5 - 2.0		0.5 - 2.0		0.5 - 2.0		0.5 - 2.0
Expected volatility	67.8 - 79.8	%	67.8 - 79.6	%	67.8 - 79.8	%	67.8 - 79.6	%
Risk-free interest rate	.47% - 1.09	%	.47% - .93	%	.47% - 1.09	%	.47% - .93	%
Expected dividend yield	—	%	—	%	—	%	—	%