Stock-Based Compensation Expense (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Effect of Recording Stock-Based Compensation Expense

The effect of recording stock-based compensation expense for the three and six months ended June 30, 2018 and 2017 is as follows (in thousands):

	Three Months Ended						Six Months Ended
	June 30, 2018			June 30, 2017			June 30, 2018			June 30, 2017
Research, development and other related costs	$	3,344		$	3,437		$	6,438		$	6,134
Selling, general and administrative	3,875			5,087			8,189			9,451
Total stock-based compensation expense	7,219			8,524			14,627			15,585
Tax effect on stock-based compensation expense	(1,159		)	(2,359		)	(2,415		)	(4,379		)
Net effect on net income (loss)	$	6,060		$	6,165		$	12,212		$	11,206

Stock-Based Compensation Expense Categorized by Equity Components

Stock-based compensation expense categorized by various equity components for the three and six months ended June 30, 2018 and 2017 is summarized in the table below (in thousands):

	Three Months Ended				Six Months Ended
	June 30, 2018		June 30, 2017		June 30, 2018		June 30, 2017
Employee stock options	$	106	$	586	$	283	$	1,231
Restricted stock awards and units	6,379		7,301		12,810		13,287
Employee stock purchase plan	734		637		1,534		1,067
Total stock-based compensation expense	$	7,219	$	8,524	$	14,627	$	15,585

Schedule of Assumptions Used To Value Options Granted

ESPP grants occur in February and August. The following assumptions were used to value the ESPP shares for these grants:

	February 2018		February 2017
Expected life (years)	2.0		2.0
Risk-free interest rate	2.2	%	1.2	%
Dividend yield	3.6	%	2.0	%
Expected volatility	39.4	%	28.3	%