Shared Based Awards (Tables)

12 Months Ended

Dec. 31, 2013

Share Based Awards [Abstract]

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]

	Year ended December 31,
	2013	2012	2011
Stock compensation expense	5,434	5,563	4,016
Tax benefit from stock-based compensation cost	2,052	1,922	1,376
Indirect tax benefit	866	209	785

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Year ended December 31,
	2013			2012			2011
Number of options granted	244,440			228,328			290,000
Grant date fair value of options granted (in thousands)	$	3,934		$	3,158		$	4,090
Weighted average assumptions for stock option valuation:
Expected term (years)	4.6			4.7			5.0
Expected stock price volatility	29.2		%	33.6		%	34.5		%
Risk-free interest rate	0.8		%	0.7		%	1.7		%
Expected dividend yield	—		%	—		%	—		%
Weighted average grant price per option	$	62.12		$	47.12		$	43.27
Weighted average grant date fair value per option	$	16.09		$	13.83		$	14.10

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

A summary of our stock option activity as of and for the year ended December 31, 2013 is as follows:

	Shares		Weighted Average Exercise Price Per Share		Weighted Average Contractual Life (Years)	Aggregate Intrinsic Value
Outstanding at December 31, 2012	2,444,753		$	35.66
Granted	244,440		$	62.12
Exercised	(715,779	)	$	34.48
Forfeited or expired	(21,290	)	$	48.75
Outstanding at December 31, 2013	1,952,124		$	39.26	5.1	$	47,783
Exercisable at December 31, 2013	1,392,417		$	35.18	4.0	$	39,726
Vested and expected to vest, December 31, 2013	1,952,124		$	39.26	5.1	$	47,783

Exercised Options Data [Table Text Block]

	Year ended December 31,
	2013		2012		2011
Intrinsic value of options exercised	$	21,847	$	12,211	$	11,451
Cash received from exercise of stock options	$	18,004	$	14,844	$	7,974
Tax benefit from stock option exercises	$	6,966	$	4,567	$	4,288

Schedule of restricted stock activity [Table Text Block]

	Year ended December 31,
	2013		2012		2011
PRSU
Shares granted	15,085		15,589		—
Grant date fair value per share	$	50.82	$	43.60	$	—
Grant date fair value	$	767	$	680	$	—
Intrinsic value vested	$	636
RSU
Shares granted	4,908		6,132		—
Grant date fair value per share	$	67.25	$	53.81	$	—
Grant date fair value	$	330	$	330	$	—
Intrinsic value vested	$	412

Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]

	Number of Units		Grant Date Fair Value Per Share		Weighted Average Contractual Life (Years)	Aggregate Intrinsic Value
Non-vested at December 31, 2012	37,310		$	45.28
Granted	19,993		$	54.85
Vested	(16,526	)	$	47.39
Forfeited	(15,085	)	$	50.82
Non-vested and expected to vest at December 31, 2013	25,692		$	48.12	0.5	$	1,637

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block]

	Year ended December 31,
	2013			2012			2011
ESPP shares purchased by employees	50,944			61,004			57,643
Intrinsic value of ESPP purchases (in thousands)	$	840		$	913		$	530
Weighted average assumptions for ESPP valuation:
Expected term (in years)	0.5			0.5			0.5
Expected stock price volatility	24.4		%	23.6		%	26.0		%
Risk-free interest rate	0.1		%	0.1		%	0.4		%
Expected dividend yield	—		%	—		%	—		%