Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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, 2016	4,115	9,043	$	5.72	7.55	$	55,396
Additional shares authorized	2,107	—
Options granted	(2,078)	2,078	$	10.55
Options exercised	—	(565)	$	4.10
Options forfeited	593	(593)	$	10.37
Balance at December 31, 2017	4,737	9,963	$	6.54	7.03	$	31,902
Exercisable at December 31, 2017		6,103	$	4.41	5.95	$	30,201
Vested and expected to vest at December 31, 2017		9,592	$	6.41	6.96	$	31,738

Restricted stock units

		Weighted-
		Average
	Number of	Grant Date
	Shares	Fair Value
Balance at December 31, 2016	159	$	9.80
Granted	345	$	10.48
Vested	(64)	$	9.79
Canceled/Forfeited	(51)	$	10.17
Balance at December 31, 2017	389	$	10.38

Summary of stock-based compensation expenses

	Year ended December 31,
	2017						2016						2015
	Employee		Non-Employee		Total		Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	544	$	—	$	544	$	651	$	(10)	$	641	$	351	$	241	$	592
Research and development		3,214		—		3,214		2,829		24		2,853		1,566		9		1,575
Selling, general and administrative		7,644		—		7,644		6,837		270		7,107		4,993		166		5,159
Total	$	11,402	$	—	$	11,402	$	10,317	$	284	$	10,601		6,910	$	416	$	7,326

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,
	2017					2016					2015
Expected term (years)	5.14		—	5.24		5.10		—	5.20		5.58		—	10.00
Expected volatility	40.75	%	—	62.93	%	63.06	%	—	72.49	%	69.65	%	—	78.82	%
Expected dividend rate				0	%				0	%				0	%
Risk-free interest rate	1.67	%	—	2.16	%	0.97	%	—	1.92	%	1.56	%	—	2.32	%

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,
	2017					2016					2015
Expected term (years)	2.67		—	2.71		2.65		—	3.16		4.94		—	9.78
Expected volatility	41.22	%	—	52.18	%	50.90	%	—	72.61	%	70.17	%	—	75.35	%
Expected dividend rate				0	%				0	%				0	%
Risk-free interest rate	1.42	%	—	1.95	%	0.68	%	—	1.38	%	1.74	%	—	2.24	%