Stock Plans (Tables)

9 Months Ended

Sep. 30, 2016

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of allocation of stock-based compensation expense

Stock-based compensation cost included in cost of revenue; selling, general and administrative expense; and research and development expense is as follows (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2016		2015		2016		2015
Cost of revenue	$	146	$	186	$	643	$	539
Selling, general and administrative	799		708		2,436		1,732
Research and development	152		161		680		635
Total stock-based compensation expense	$	1,097	$	1,055	$	3,759	$	2,906

Stock options

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of valuation assumptions for fair value of stock options granted

The fair value of the stock options granted during the three and nine months ended September 30, 2015 was estimated using the Black-Scholes valuation model with the following weighted average assumptions:

	Three Months Ended		Nine Months Ended
	September 30,		September 30,
	2015		2015
Expected dividend yield	—	%	—	%
Expected volatility	60	%	61	%
Risk-free interest rate	1.60	%	1.59	%
Expected term (in years)	5.0		5.0

Restricted stock unit awards

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of RSU expense by vesting type

The following table summarizes the amount of compensation expense recognized for RSUs for the three and nine months endedSeptember 30, 2016 and 2015 (in thousands):

	Three Months Ended September 30,					Nine Months Ended September 30,
RSU Type	2016		2015			2016		2015
Service-based	$	544	$	400		$	1,613	$	975
Performance objectives	30		(60		)	71		(28		)
Market-condition	250		34			621		102
	$	824	$	374		$	2,305	$	1,049

Performance restricted stock unit awards

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of market-condition awards fair value assumptions

The fair value of the market-condition PSUs granted was calculated using a Monte Carlo valuation model with the following assumptions:

	Nine Months Ended
	September 30,
	2016
Expected dividend yield	—	%
Expected volatility	62	%
Risk-free interest rate	1.07	%
Expected term (in years)	3.0

Employee stock purchase plan

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of employee stock purchase plan fair value assumptions

The fair value of the ESPP shares for the three and nine months ended September 30, 2016 and 2015 was estimated using the Black-Scholes valuation model for a call and a put option with the following weighted-average assumptions:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2016			2015			2016			2015
Expected dividend yield	—		%	—		%	—		%	—		%
Expected volatility	54		%	68		%	58		%	58		%
Risk-free interest rate	0.36		%	0.01		%	0.45		%	0.08		%
Expected term (in years)	0.5			0.5			0.5			0.5
Fair value per share	$	1.59		$	1.54		$	2.04		$	1.74