Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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	(1,568)	1,568	$	10.23
Options exercised	—	(280)	$	3.36
Options forfeited/cancelled	380	(380)	$	10.23
Balance at June 30, 2017	5,034	9,951	$	6.33	7.44	$	46,865
Exercisable at June 30, 2017		5,415	$	3.89	6.25	$	38,550
Vested and expected to vest at June 30, 2017		9,509	$	6.19	7.37	$	46,054

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	295	$	10.25
Vested	(51)	$	9.70
Canceled/forfeited	(20)	$	9.64
Balance at June 30, 2017	383	$	10.16

Summary of stock-based compensation expenses

	Three months ended  June 30,
	2017						2016
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	139	$	13	$	152	$	157	$	32	$	189
Research and development		730		—		730		716		1		717
Selling, general and administrative		1,992		3		1,995		1,940		51		1,991
Total	$	2,861	$	16	$	2,877	$	2,813	$	84	$	2,897

	Six months ended June 30,
	2017						2016
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	282	$	1	$	283	$	315	$	7	$	322
Research and development		1,380		—		1,380		1,321		—		1,321
Selling, general and administrative		3,756		1		3,757		3,401		248		3,649
Total	$	5,418	$	2	$	5,420	$	5,037	$	255	$	5,292

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  June 30,										Six months ended June 30,
	2017					2016					2017					2016
Expected term (years)	5.1		—	5.2		5.1		—	5.2		5.1		—	5.2		5.1		—	5.2
Expected volatility	62.7	%	—	62.9	%	68.5	%	—	69.2	%	62.7	%	—	62.9	%	68.5	%	—	71.0	%
Expected dividend rate				0	%				0	%				0	%				0	%
Risk-free interest rate	1.80	%	—	1.87	%	1.18	%	—	1.24	%	1.80	%	—	1.91	%	1.18	%	—	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  June 30,						Six months ended June 30,
	2017			2016			2017					2016
Expected term (years)		2.7			2.8					2.7		2.8		—	3.2
Expected volatility		52.2	%		56.5	%	51.7	%	—	52.2	%	56.5	%	—	72.6	%
Expected dividend rate		0	%		0	%				0	%				0	%
Risk-free interest rate		1.50	%		0.68	%	1.42	%	—	1.50	%	0.68	%	—	0.90	%