Stock Plans (Tables)

12 Months Ended

Dec. 31, 2017

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

Stock Options Activity

The following table summarizes total aggregate stock option activity for the year ended December 31, 2017 (in thousands, except for per share data):

	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Balance at December 31, 2016	414		$	8.97
Granted	50		5.56
Cancelled	(103	)	10.56
Balance at December 31, 2017	361		$	8.05	5.72	$	67
Vested or expected to vest at December 31, 2017	354		$	8.09	5.68	$	65
Exercisable at December 31, 2017	220		$	9.20	4.39	$	30

Stock Options, Valuation Assumptions

The fair value of the stock options granted during the years ended December 31, 2017 and 2015 was estimated using the Black-Scholes valuation model using the following assumptions:

	Years Ended December 31,
	2017		2015
Expected dividends	—	%	—	%
Expected volatility range	58% to 59%		60% to 61%
Expected volatility weighted average	59	%	60	%
Risk-free interest rate	1.9	%	1.6	%
Expected life/term weighted average (in years)	5.5		4.9

Nonvested Restricted Stock Units Activity

The following table summarizes RSU activity for both service-based awards and performance-based awards for the year ended December 31, 2017 (in thousands, except for per share data):

	Shares		Weighted Average Grant Date Fair Value
Nonvested at December 31, 2016	1,748		$	6.40
Granted	1,796		5.89
Released	(540	)	5.86
Forfeited	(354	)	6.45
Nonvested at December 31, 2017	2,650		$	6.16

Stock-based Compensation Expense Allocation

Compensation cost for stock options, RSAs, RSUs, ESPP, bonuses and director fees is as follows (in thousands):

	Years Ended December 31,
	2017		2016		2015
Stock options	$	237	$	171	$	232
Restricted stock awards	416		388		1,974
Restricted stock units	5,186		3,215		1,462
ESPP	114		231		278
Bonuses settled in stock	2,826		1,359		—
Director fees settled in stock	258		—		—
Total stock-based compensation expense	$	9,037	$	5,364	$	3,946

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

	Years Ended December 31,
	2017		2016		2015
Cost of revenue	$	1,070	$	854	$	644
Selling, general and administrative	6,606		3,674		2,502
Research and development	1,361		836		800
Total stock-based compensation expense	$	9,037	$	5,364	$	3,946

Employee Stock Purchase Plan, Valuation Assumptions

The fair value of ESPP awards was calculated using the following weighted-average assumptions:

	Years Ended December 31,
	2017			2016			2015
Expected dividends	—		%	—		%	—		%
Expected volatility	34		%	57		%	57		%
Risk-free interest rate	0.89		%	0.43		%	0.29		%
Expected life (in years)	0.45			0.5			0.5
Fair value per share	$	1.30		$	1.93		$	1.86

Schedule of Stock Plan Shares Reserved for Future Issuance

The following table summarizes the shares available for grant under the Company’s stock-based compensation plans as of December 31, 2017:

2013 Omnibus Equity Incentive Plan	3,138,321
2004 Employee Stock Purchase Plan	617,609
Total	3,755,930

Unvested restricted stock awards

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

Nonvested Restricted Stock Shares Activity

The following table summarizes RSA activity for the year ended December 31, 2017 (in thousands, except for per share data):

	Shares		Weighted Average Grant Date Fair Value
Nonvested at December 31, 2016	88		$	13.37
Vested	(53	)	12.58
Forfeited	(9	)	14.57
Nonvested at December 31, 2017	26		$	14.57

Unvested restricted stock unit awards

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

Schedule of Share-based Payment Award, Market-condition PSUs, Valuation Assumptions [Table Text Block]

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

	Years Ended December 31,
	2017		2016
Expected dividend yield	—	%	—	%
Expected volatility	53	%	62	%
Risk-free interest rate	1.55	%	1.07	%
Expected term (in years)	2.8		3.0

Stock-based Compensation Expense Allocation

The following table summarizes the amount of compensation expense recognized for RSUs for the years ended December 31, 2017, 2016 and 2015 (in thousands):

	Years Ended December 31,
RSU Type	2017		2016		2015
Service-based	$	3,268	$	2,243	$	1,362
Performance objectives	379		103		(28		)
Market-condition	1,539		869		128
	$	5,186	$	3,215	$	1,462