Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

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, 2017	4,737	9,963	$	6.54	7.03	$	31,902
Additional shares authorized	2,161	—
Options granted	(2,319)	2,319	$	11.77
Options exercised	—	(1,967)	$	6.78
Options forfeited	852	(852)	$	7.54
Balance at December 31, 2018	5,431	9,463	$	7.69	6.91	$	61,718
Exercisable at December 31, 2018		5,484	$	5.25	5.57	$	48,055
Vested and expected to vest at December 31, 2018		9,224	$	7.60	6.87	$	60,895

Restricted stock units

		Weighted-
		Average
	Number of	Grant Date
	Shares	Fair Value
Balance at December 31, 2017	389	$	10.38
Granted	953	$	11.86
Vested	(177)	$	13.84
Canceled/Forfeited	(81)	$	9.91
Balance at December 31, 2018	1,084	$	11.72

Summary of stock-based compensation expenses

	Year ended December 31,
	2018						2017						2016
	Employee		Non-Employee		Total		Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	564	$	5	$	569	$	544	$	—	$	544	$	651	$	(10)	$	641
Research and development		4,043		—		4,043		3,214		—		3,214		2,829		24		2,853
Selling, general and administrative		9,474		112		9,586		7,644		—		7,644		6,837		270		7,107
Total	$	14,081	$	117	$	14,198	$	11,402	$	—	$	11,402	$	10,317	$	284	$	10,601

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,
	2018					2017					2016
Expected term (years)	5.24		—	5.62		5.14		—	5.24		5.10		—	5.20
Expected volatility	40.28	%	—	42.53	%	40.75	%	—	62.93	%	63.06	%	—	72.49	%
Expected dividend rate				0	%				0	%				0	%
Risk-free interest rate	2.37	%	—	3.06	%	1.67	%	—	2.16	%	0.97	%	—	1.92	%

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,
	2018					2017					2016
Expected term (years)	2.72		—	2.76		2.67		—	2.71		2.65		—	3.16
Expected volatility	41.36	%	—	43.84	%	41.22	%	—	52.18	%	50.90	%	—	72.61	%
Expected dividend rate				0	%				0	%				0	%
Risk-free interest rate	2.36	%	—	2.86	%	1.42	%	—	1.95	%	0.68	%	—	1.38	%