Stock-Based Awards (Tables)

6 Months Ended

Jun. 30, 2017

Stock-Based Awards

Assumptions used to determine fair value of stock options granted

	Six Months Ended
	June 30,
	2017		2016
Risk-free interest rate	1.93	%	1.44	%
Expected term (in years)	6.0		6.6
Expected volatility	94.09	%	96.90	%
Expected dividend yield	0	%	0	%

Summary of stock option activity

					Weighted
			Weighted		Average
			Average		Remaining	Aggregate
	Number		Exercise		Contractual	Intrinsic
	of Shares		Price		Term	Value
					(in years)
Outstanding as of December 31, 2016	2,702,350		$	18.94	9.05	$	24,434
Granted	135,000			27.19
Exercised	(36,738)			6.40
Forfeited and cancelled	(27,546)			(17.55)
Outstanding as of June 30, 2017	2,773,066		$	19.53	8.64	$	23,461
Options vested and expected to vest as of June 30, 2017	2,773,066		$	19.53	8.64	$	23,461
Options exercisable as of June 30, 2017	736,308	(1)	$	11.02	7.99	$	12,043

(1) All options granted under the 2012 Plan are exercisable immediately, subject to a repurchase right in the Company’s favor that lapses as the option vests. This amount reflects the number of shares under options that were vested, as opposed to exercisable, as of June  30, 2017.

Summary of restricted stock activity

		Weighted
		Average
		Grant Date
	Number	Fair Value
	of Shares	Per Share
Outstanding as of December 31, 2016	219,614	$	27.43
Granted	13,167		28.50
Vested	(7,799)		20.26
Forfeited and cancelled	(2,096)		25.08
Outstanding as of June 30, 2017	222,886	$	27.76

Stock-based compensation expense

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2017		2016		2017		2016
Research and development	$	1,304	$	533	$	2,521	$	954
General and administrative		2,000		821		3,936		1,622
Total stock-based compensation expense	$	3,304	$	1,354	$	6,457	$	2,576