Share-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

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

Schedule of Share-based Compensation, Restricted Stock Units Award Activity

RSU activity for the six months ended June 30, 2018 is as follows:

	Number of		Weighted-Average Grant-Date
(in thousands, except weighted-average fair value prices)	Shares		Fair Value
Unvested RSUs outstanding at December 31, 2017	1,309		$	37.54
RSUs granted	530		$	46.73
RSUs vested	(617	)	$	37.01
RSUs forfeited	(26	)	$	40.68
Unvested RSUs outstanding at June 30, 2018	1,196		$	41.81

Schedule of Share-based Payment Award, Performance-Based Units, Valuation Assumptions

The fair values of the awards containing market-based vesting conditions were estimated using Monte-Carlo simulation with the following weighted-average assumptions:

	For the Six Months Ended June 30,
	2018		2017
Expected dividend yield	—	%	—	%
Risk-free interest rate (1)	2.38	%	1.47	%
Expected volatility (2)	23.63	%	27.83	%
Average total stockholder return (2)	6.11	%	1.46	%

(1) The risk-free interest rate for the periods within the contractual term of the PBRSUs is based on the U.S. Treasury yield curve in effect at the time of the grant.

(2) The expected volatility and average total stockholder return are measures of the amount by which a stock price has fluctuated or is expected to fluctuate based primarily on our and our peers' historical data.

Schedule of Other Share-based Compensation, Activity

PBRSU activity for the six months ended June 30, 2018 is as follows:

	Number of		Weighted-Average Grant-Date
(in thousands, except weighted-average fair value prices)	Shares		Fair Value
Unvested PBRSUs outstanding at December 31, 2017	659		$	37.22
PBRSUs granted	327		$	46.28
PBRSUs vested	(239	)	$	39.91
PBRSUs forfeited	(43	)	$	39.10
Unvested PBRSUs outstanding at June 30, 2018	704		$	41.11

Schedule of Share-based Compensation, Stock Options, Activity

Option activity for the six months ended June 30, 2018 is as follows:

(in thousands, except weighted-average price)	Number of Shares		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term	Aggregate Intrinsic Value
Options outstanding at December 31, 2017	1,186		$	20.67
Options exercised	(594	)	$	21.28
Options vested, exercisable, and outstanding at June 30, 2018	592		$	20.07	3.5	$	18,829

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan

The following table sets forth the share-based compensation expense recognized for the three and six months ended June 30, 2018 and 2017.

	For the Three Months Ended				For the Six Months Ended
	June 30,				June 30,
(in thousands)	2018		2017		2018		2017
RSUs	$	7,238	$	6,596	$	14,633	$	16,378
PBRSUs	3,445		1,809		4,159		3,477
Stock options	—		—		—		144
Employee stock purchase plan	439		367		1,007		940
	$	11,122	$	8,772	$	19,799	$	20,939