Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2018

Schedule of stock-based compensation

The following table summarizes stock-based compensation expense related to all of the Company’s stock awards included by operating expense categories, as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Cost of revenues	$	1,300	$	471	$	2,412	$	2,208
Research and development	1,802		953		3,342		2,980
Selling, general and administrative	4,536		1,214		9,070		5,561
Total stock-based compensation expense	$	7,638	$	2,638	$	14,824	$	10,749

The following table summarizes stock-based compensation expense related to all of the Company’s stock awards included by award types, as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Stock options	$	1,980	$	1,535	$	3,740	$	2,988
Restricted stock awards	5,658		1,036		11,084		7,431
Employee Stock Purchase Plan	—		67		—		330
Total stock-based compensation before taxes	$	7,638	$	2,638	$	14,824	$	10,749
Tax benefit	$	531	$	506	$	2,954	$	1,713

Stock options

Schedule of fair value assumptions

The Company uses the Black-Scholes option pricing model for determining the estimated fair value for stock options. The weighted-average assumptions used in the Black-Scholes option pricing model are as follows: 

	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
Expected stock price volatility	65.1		%	53.2		%	65.1		%	49.2		%
Risk-free interest rate	2.6		%	1.7		%	2.5		%	1.7		%
Expected life of options (in years)	4.08			4.05			4.08			4.03
Expected dividend yield	0.0		%	0.0		%	0.0		%	0.0		%
Weighted-average fair value (grant date) of the options	$	5.47		$	6.87		$	5.34		$	7.79

Schedule of information about stock options outstanding

The following table summarizes information about stock options outstanding as of June 30, 2018: 

Options	Number of Options		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding at December 31, 2017	3,950		$	21.54
Options Granted	902		10.37
Options Exercised	—		—
Options Cancelled	(290	)	24.40
Outstanding at June 30, 2018	4,562		$	19.15	5.37	$	566
Vested at June 30, 2018	1,420		$	30.97	3.46	$	—
Exercisable at June 30, 2018	1,420		$	30.97	3.46	$	—

Restricted stock awards

Schedule of unvested restricted stock

A summary of the Company’s unvested restricted stock at June 30, 2018, and changes during the six months ended June 30, 2018, is presented below:

Unvested Restricted Stock	Number of Awards		Weighted- Average Grant Date Fair Value
Unvested at December 31, 2017	2,064		$	22.75
Granted	1,329		10.17
Vested	(499	)	30.27
Forfeited	(109	)	19.56
Unvested at June 30, 2018	2,785		$	15.45