Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 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	2,162	—
Options granted	(1,697)	1,697	$	11.24
Options exercised	—	(1,774)	$	6.80
Options forfeited/cancelled	759	(759)	$	7.23
Balance at September 30, 2018	5,961	9,127	$	7.31	6.97	$	151,881
Exercisable at September 30, 2018		5,348	$	5.01	5.75	$	101,241
Vested and expected to vest at September 30, 2018		8,908	$	7.23	6.93	$	148,943

Restricted stock units

		Weighted-
		Average
		Grant Date
(in thousands, except for grant date fair value)	Shares	Fair Value
Balance at December 31, 2017	389	$	10.38
Granted	923	$	11.72
Vested	(146)	$	13.02
Canceled/forfeited	(77)	$	9.78
Balance at September 30, 2018	1,089	$	11.56

Summary of stock-based compensation expenses

	Three months ended  September 30,
	2018						2017
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	176	$	15	$	191	$	138	$	9	$	147
Research and development		1,047		—		1,047		943		—		943
Selling, general and administrative		2,292		86		2,378		1,894		2		1,896
Total	$	3,515	$	101	$	3,616	$	2,975	$	11	$	2,986

	Nine months ended September 30,
	2018						2017
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	466	$	20	$	486	$	420	$	10	$	430
Research and development		2,963		—		2,963		2,323		—		2,323
Selling, general and administrative		6,606		83		6,689		5,650		3		5,653
Total	$	10,035	$	103	$	10,138	$	8,393	$	13	$	8,406

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

	Three months ended  September 30,									Nine months ended September 30,
	2018					2017				2018					2017
Expected term (years)	5.35		—	5.50		5.22	—	5.23		5.24		—	5.62		5.14		—	5.23
Expected volatility	40.59	%	—	41.05	%	62.27	—	62.49	%	40.28	%	—	41.05	%	62.27	%	—	62.93	%
Expected dividend rate				0.00	%			0.00	%				0.00	%				0.00	%
Risk-free interest rate	2.75	%	—	2.97	%	1.67	—	1.90	%	2.37	%	—	2.97	%	1.67	%	—	1.90	%

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

	Three months ended  September 30,						Nine months ended September 30,
	2018			2017			2018					2017
Expected term (years)		2.76			2.70		2.72		—	2.76		2.67		—	2.70
Expected volatility		41.36	%		51.28	%	41.36	%	—	42.03	%	51.28	%	—	52.18	%
Expected dividend rate		0.00	%		0.00	%				0.00	%				0.00	%
Risk-free interest rate		2.86	%		1.58	%	2.36	%	—	2.86	%	1.42	%	—	1.58	%