Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 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	(1,921)	1,921	$	10.41
Options exercised	—	(474)	$	3.87
Options forfeited/cancelled	531	(531)	$	10.45
Balance at September 30, 2017	4,832	9,959	$	6.46	7.27	$	64,602
Exercisable at September 30, 2017		5,498	$	4.08	6.09	$	48,763
Vested and expected to vest at September 30, 2017		9,536	$	6.33	7.21	$	63,102

Restricted stock units

		Weighted-
		Average
		Grant Date
(in thousands, except for grant date fair value)	Shares	Fair Value
Balance at December 31, 2016	159	$	9.80
Granted	313	$	10.39
Vested	(57)	$	9.70
Canceled/forfeited	(36)	$	10.09
Balance at September 30, 2017	379	$	10.28

Summary of stock-based compensation expenses

	Three months ended  September 30,
	2017						2016
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	138	$	9	$	147	$	164	$	(4)	$	160
Research and development		943		—		943		784		(1)		783
Selling, general and administrative		1,894		2		1,896		1,716		14		1,730
Total	$	2,975	$	11	$	2,986	$	2,664	$	9	$	2,673

	Nine months ended September 30,
	2017						2016
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	420	$	10	$	430	$	479	$	3	$	482
Research and development		2,323		—		2,323		2,105		(1)		2,104
Selling, general and administrative		5,650		3		5,653		5,117		262		5,379
Total	$	8,393	$	13	$	8,406	$	7,701	$	264	$	7,965

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,
	2017					2016					2017					2016
Expected term (years)				5.2					5.2		5.1		—	5.2		5.1		—	5.2
Expected volatility	62.3	%	—	62.5	%	69.0	%	—	72.5	%	62.3	%	—	62.9	%	68.5	%	—	72.5	%
Expected dividend rate				0	%				0	%				0	%				0	%
Risk-free interest rate	1.67	%	—	1.90	%	0.97	%	—	1.12	%	1.67	%	—	1.90	%	0.97	%	—	1.24	%

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,
	2017			2016			2017					2016
Expected term (years)		2.7			2.8					2.7		2.8		—	3.2
Expected volatility		51.3	%		50.9	%	51.3	%	—	52.2	%	50.9	%	—	72.6	%
Expected dividend rate		0	%		0	%				0	%				0	%
Risk-free interest rate		1.58	%		0.85	%	1.42	%	—	1.58	%	0.68	%	—	0.90	%