Stock-Based Compensation (Tables)

9 Months Ended

Sep. 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 September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	(in thousands)
Stock options	$	717	$	602	$	1,974	$	1,741
Restricted stock units	4,170		4,595		12,538		10,834
Unrestricted stock awards	232		225		742		725
Phantom stock units	626		371		1,510		658
Total stock-based compensation	$	5,745	$	5,793	$	16,764	$	13,958
Related tax benefit	$	1,192	$	1,289	$	3,520	$	3,793

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	191		40.40					$	13.27
Exercised	(35	)	35.31			214
Forfeited	(36	)	35.29
Expired	(312	)	55.11
Outstanding, September 30, 2016	988		$	45.57	6.8	$	13,732
Outstanding, January 1, 2017	959		$	45.64	6.6	$	19,125
Granted	135		65.94					$	21.98
Exercised	(36	)	38.68			972
Forfeited	(35	)	47.38
Expired	(47	)	67.43
Outstanding, September 30, 2017	976		$	47.60	6.5	$	30,320
Exercisable September 30, 2017	631		$	47.36	5.3	$	20,197
Expected to vest, September 30, 2017	344		$	48.03	8.6	$	10,123

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 September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
Expected volatility	29.0		%	33.7		%	32.5		%	33.5		%
Risk-free interest rate	1.8		%	1.3		%	2.0		%	1.3		%
Expected term (years)	5.5			5.5			5.5			5.5
Weighted average fair value	$	21.84		$	17.37		$	21.98		$	13.27

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	196		$	41.58
Released	(280	)			$	10,823
Forfeited	(50	)
Outstanding, September 30, 2016	622
Outstanding, January 1, 2017	701		$	38.04
Granted	141		65.54
Released	(340	)	38.51		$	13,097
Forfeited	(23	)	45.27
Outstanding, September 30, 2017	479		45.64
Vested but not released, September 30, 2017	9				$	660
Expected to vest, September 30, 2017	388				$	30,013

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 September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
Expected volatility	27.9		%	28.8		%	28.0		%	30.0		%
Risk-free interest rate	1.4		%	0.8		%	1.0		%	0.7		%
Expected term (years)	2.3			2.3			1.7			1.8
Weighted average fair value	$	80.64		$	63.10		$	77.75		$	44.92

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, September 30, 2016	62
Expected to vest, September 30, 2016	56
Outstanding, January 1, 2017	62		$	40.11
Granted	32		65.55
Released	(20	)	40.11
Forfeited	(7	)	41.61
Outstanding, September 30, 2017	67		52.24
Expected to vest, September 30, 2017	67