Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

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

Schedule of Stock-Based Compensation Expense

Stock-based compensation expense related to ESPP purchase rights and RSUs is summarized as follows (in thousands):

	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
Stock-based compensation expense by type of awards
RSUs	$	9,883		$	6,093		$	15,206		$	15,330
ESPP purchase rights	1,903			1,520			3,349			2,563
Total stock-based compensation expense	11,786			7,613			18,555			17,893
Income tax benefit	(1,831		)	(2,531		)	(2,670		)	(5,404		)
Stock-based compensation expense, net of tax	$	9,955		$	5,082		$	15,885		$	12,489

Schedule of ESPP Purchase Rights and Underlying Weighted Average Assumptions

The estimated weighted average fair value per share and underlying assumptions of ESPP purchase rights issued were as follows:

ESPP Purchase Rights:	Six Months Ended June 30,
	2018		2017
Weighted average fair value per share	$	9.03	$	12.03
Expected volatility	59% - 107%		24% - 28%
Risk-free interest rate	1.6% - 2.2%		0.7% - 1.2%
Expected term (in years)	0.5 - 2.0		0.5 - 2.0

Schedule of Non-Vested RSUs

Non-vested RSU activity during the six months ended June 30, 2018 are summarized below (shares in thousands):

	Time-based				Performance-based				Market-based			Total
	Shares		Weighted average grant date fair value		Shares		Weighted average grant date fair value		Shares	Weighted average grant date fair value		Shares		Weighted average grant date fair value
Non-vested at January 1, 2018	1,048		$	35.76	1,209		$	42.18	23	$	35.15	2,280		$	39.16
Granted	491		28.03		478		28.26		—	—		969		28.14
Vested	(106	)	32.44		(20	)	44.83		—	—		(126	)	34.42
Forfeited	(67	)	35.67		(579	)	45.35		—	—		(646	)	44.34
Non-vested at June 30, 2018	1,366		33.24		1,088		34.32		23	35.15		2,477		33.73

Schedule of Weighted Average Grant Date Fair Value Per Share of Performance-Based RSUs Assumptions Used to Estimate Fair Value

The weighted average grant date fair value per share of performance-based RSUs granted and the assumptions used to estimate grant date fair value are as follows:

	Short-term		Long-term
Six Months Ended June 30, 2018
Grant date fair value per share	$	28.26	$	—
Service period (years)	1.0		N/A
Six Months Ended June 30, 2017
Grant date fair value per share	$	47.23	$	45.96
Service period (years)	1.0		2.0 - 3.0