Stock‑Based Compensation (Tables)

12 Months Ended

Dec. 31, 2015

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Summary of stock option activity

	Outstanding Options
					Weighted-
			Weighted-		Average
	Shares		Average		Remaining	Aggregate
	Available for	Number of	Exercise		Contractual	Intrinsic
(in thousands, except for contractual life and exercise price)	Grant	Shares	Price		Life	Value
					(In years)
Balance at December 31, 2014	294	8,463	$	2.28	8.83	$	43,659
Additional shares authorized	4,985	—
Options granted	(2,181)	2,181	$	10.16
Options exercised	—	(683)	$	1.72
Options forfeited	645	(645)	$	5.25
Balance at December 31, 2015	3,743	9,316	$	3.96	8.31	$	63,713
Exercisable at December 31, 2015		5,602	$	1.90	5.31	$	49,880
Vested and expected to vest at December 31, 2015		8,414	$	3.72	7.32	$	59,529

Summary of stock-based compensation expenses

	Year ended December 31,
	2015						2014						2013
	Employee		Non-Employee		Total		Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	351	$	241	$	592	$	262	$	29	$	291	$	55	$	7	$	62
Research and development		1,566		9		1,575		1,563		30		1,593		612		4		616
Selling, general and administrative		4,993		166		5,159		3,180		93		3,273		970		9		979
Total	$	6,910	$	416	$	7,326	$	5,005	$	152	$	5,157		1,637	$	20	$	1,657

Employee stock options

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of assumptions used in valuation of fair value of employee stock options

	Year ended December 31,
	2015					2014					2013
Expected term	5.6		—	10.0		4.91		—	7.06		6.0
Expected volatility	69.7	%	—	78.8	%	73.4	%	—	87.0	%	63.7	%	—	85.7	%
Expected dividend rate				0	%				0	%				0	%
Risk-free interest rate	1.56	%	—	2.32	%	1.65	%	—	2.04	%	0.44	%	—	2.86	%

Non-employee stock options

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of assumptions used in valuation of fair value of employee stock options

	Year ended December 31,
	2015					2014					2013
Expected term	4.9		—	9.8		4.4		—	10.0		8.4
Expected volatility	70.2	%	—	75.4	%	71.9	%	—	80.2	%	75.6	%	—	81.5	%
Expected dividend rate				0	%				0	%				0	%
Risk-free interest rate	1.74	%	—	2.24	%	1.41	%	—	2.61	%	1.44	%	—	2.51	%