Stock-Based Compensation (Tables)

3 Months Ended

Mar. 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	(146)	146	$	9.37
Options exercised	—	(128)	$	3.23
Options forfeited/cancelled	287	(287)	$	10.26
Balance at March 31, 2017	6,363	8,774	$	5.67	7.23	$	33,558
Exercisable at March 31, 2017		4,919	$	3.17	6.13	$	29,209
Vested and expected to vest at March 31, 2017		8,398	$	5.53	7.17	$	33,134

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	5	$	9.37
Vested	(15)	$	9.59
Canceled/forfeited	(11)	$	9.69
Balance at March 31, 2017	138	$	9.82

Summary of stock-based compensation expenses

	Three months ended  March 31,
	2017						2016
	Employee		Non-Employee		Total		Employee		Non-Employee		Total
	(in thousands)
Cost of revenues	$	143	$	(12)	$	131	$	158	$	(25)	$	133
Research and development		650		—		650		606		(1)		605
Selling, general and administrative		1,764		(2)		1,762		1,461		197		1,658
Total	$	2,557	$	(14)	$	2,543	$	2,225	$	171	$	2,396

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  March 31,
	2017			2016
Expected term		5.1		5.1		—	5.2
Expected volatility		62.7	%	70.6	%	—	71.0	%
Expected dividend rate		0	%				0	%
Risk-free interest rate		1.91	%	1.25	%	—	1.51	%

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  March 31,
	2017			2016
Expected term		2.7			3.2
Expected volatility		51.7	%		72.6	%
Expected dividend rate		0	%		0	%
Risk-free interest rate		1.42	%		0.90	%