Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2017

Share-based Compensation [Abstract]

Stock-Based Compensation Expense and Related Tax Benefit [Table Text Block]

Total stock-based compensation expense and the related tax benefit were as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
	(in thousands)
Stock options	$	598	$	585	$	1,257	$	1,139
Restricted stock units	4,071		3,143		8,368		6,239
Unrestricted stock awards	255		250		510		500
Phantom stock units	492		211		884		287
Total stock-based compensation	$	5,416	$	4,189	$	11,019	$	8,165
Related tax benefit	$	1,100	$	1,296	$	2,328	$	2,504

Employee Stock Options Activity [Table Text Block]

A summary of our stock option activity is as follows:

	Shares		Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Life	Aggregate Intrinsic Value		Weighted Average Grant Date Fair Value
	(in thousands)				(years)	(in thousands)
Outstanding, January 1, 2016	1,180		$	48.31	5.7	$	405
Granted	185		40.04					$	13.15
Exercised	(34	)	35.29			195
Forfeited	(36	)	35.29
Expired	(147	)	62.50
Outstanding, June 30, 2016	1,148		$	45.95	6.0	$	3,700
Outstanding, January 1, 2017	959		$	45.64	6.6	$	19,125
Granted	132		65.80					$	21.99
Exercised	(34	)	37.58			933
Forfeited	(35	)	47.38
Expired	(47	)	67.43
Outstanding, June 30, 2017	975		$	47.54	6.7	$	21,680
Exercisable June 30, 2017	632		$	47.38	5.5	$	14,846
Expected to vest, June 30, 2017	343		$	47.85	8.8	$	6,834

Stock Options, Valuation Assumptions [Table Text Block]

The weighted-average assumptions used to estimate the fair value of stock options granted and the resulting weighted average fair value are as follows:

	Three Months Ended June 30,						Six Months Ended June 30,
	2017			2016			2017			2016
Expected volatility	30.8		%	—		%	32.6		%	33.5		%
Risk-free interest rate	1.8		%	—		%	2.0		%	1.3		%
Expected term (years)	5.5			—			5.5			5.5
Weighted average fair value	$	21.71		$	—		$	21.99		$	13.15

Restricted Stock Units Award Activity [Table Text Block]

The following table summarizes restricted stock unit activity:

	Number of Restricted Stock Units		Weighted Average Grant Date Fair Value		Aggregate Intrinsic Value
	(in thousands)				(in thousands)
Outstanding, January 1, 2016	756
Granted	172		$	40.02
Released	(270	)			$	10,429
Forfeited	(42	)
Outstanding, June 30, 2016	616
Outstanding, January 1, 2017	701		$	38.04
Granted	140		65.48
Released	(328	)	38.26		$	12,533
Forfeited	(19	)	43.60
Outstanding, June 30, 2017	494		45.58
Vested but not released, June 30, 2017	7				$	447
Expected to vest, June 30, 2017	403				$	27,332

Restricted Stock Units, Valuation Assumptions

The weighted-average assumptions used to estimate the fair value of performance-based restricted stock units granted and the resulting weighted average fair value are as follows:

	Three Months Ended June 30,						Six Months Ended June 30,
	2017			2016			2017			2016
Expected volatility	28.0		%	—		%	28.0		%	30.0		%
Risk-free interest rate	1.4		%	—		%	1.1		%	0.7		%
Expected term (years)	2.5			—			1.7			1.8
Weighted average fair value	$	75.58		$	—		$	77.65		$	44.77

Schedule of Other Share-based Compensation, Activity [Table Text Block]

The following table summarizes phantom stock unit activity:

	Number of Phantom Stock Units		Weighted Average Grant Date Fair Value
	(in thousands)
Outstanding, January 1, 2016	—
Granted	63		$	40.11
Forfeited	(1	)
Outstanding, June 30, 2016	62
Expected to vest, June 30, 2016	55
Outstanding, January 1, 2017	62		$	40.11
Granted	32		65.55
Released	(20	)	40.11
Forfeited	(6	)	40.05
Outstanding, June 30, 2017	68		52.18
Expected to vest, June 30, 2017	68