Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2016

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

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

RSU activity for the three months ended March 31, 2016 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, 2015	1,537		$	32.92
RSUs granted	730		$	33.83
RSUs vested	(525	)	$	31.29
RSUs forfeited	(30	)	$	35.14
Unvested RSUs outstanding at March 31, 2016	1,712		$	33.77

Schedule of Share-based Payment Award, Performance-Based Units, Valuation Assumptions [Table Text Block]

The fair values of the 2016 and 2015 awards were estimated using Monte-Carlo simulation with the following weighted-average assumptions:

	For the Three Months Ended March 31,
	2016		2015
Expected dividend yield	—	%	—	%
Risk-free interest rate (1)	0.99	%	0.93	%
Expected volatility (2)	25.12	%	24.01	%
Average total stockholder return (2)	1.48	%	8.37	%

(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 is a measure 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 three months ended March 31, 2016 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, 2015	659		$	29.15
PBRSUs granted	174		$	34.29
PBRSUs vested	(88	)	$	26.04
PBRSUs forfeited	(91	)	$	19.50
Unvested PBRSUs outstanding at March 31, 2016	654		$	33.49

Schedule of Share-based Compensation, Stock Options, Activity

Option activity for the three months ended March 31, 2016 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, 2015	1,826		$	21.33
Options exercised	(165	)	$	22.42
Options outstanding at March 31, 2016	1,661		$	21.22	5.3	$	22,358
Options vested and expected to vest at March 31, 2016	1,655		$	21.20	5.3	$	22,348
Options exercisable at March 31, 2016	1,575		$	20.70	5.2	$	22,052

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

The following table sets forth the stock-based compensation expense recognized for the three months ended March 31, 2016 and 2015.

	For the Three Months Ended
	March 31,
(in thousands)	2016		2015
RSUs	$	7,019	$	6,015
PBRSUs	1,813		1,780
Stock options	383		563
Employee stock purchase plan	328		374
	$	9,543	$	8,732