Stock-Based Awards (Tables)

9 Months Ended

Sep. 30, 2017

Stock-Based Awards

Assumptions used to determine fair value of stock options granted

	Nine Months Ended
	September 30,
	2017		2016
Risk-free interest rate	1.89	%	1.41	%
Expected term (in years)	6.2		6.5
Expected volatility	93.84	%	96.60	%
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	617,500			26.47
Exercised	(36,738)			6.40
Forfeited and cancelled	(40,281)			21.09
Outstanding as of September 30, 2017	3,242,831		$	20.49	8.60	$	21,704
Options vested and expected to vest as of September 30, 2017	3,242,831		$	20.49	8.60	$	21,704
Options exercisable as of September 30, 2017	828,823	(1)	$	10.95	7.73	$	12,666

(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 September  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	88,547		26.59
Vested	(9,299)		20.32
Forfeited and cancelled	(4,531)		27.05
Outstanding as of September 30, 2017	294,331	$	27.41

Stock-based compensation expense

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2017		2016		2017		2016
Cost of revenue	$	130	$	—	$	130	$	—
Research and development		1,332		623		3,853		1,577
General and administrative		2,211		995		6,147		2,617
Total stock-based compensation expense	$	3,673	$	1,618	$	10,130	$	4,194