Shared Based Awards (Tables)

12 Months Ended

Dec. 31, 2012

Share Based Awards [Abstract]

Exercised Options Data [Table Text Block]

	Year ended December 31,
	2012		2011		2010
Intrinsic value of options exercised	$	12,211	$	11,451	$	4,422
Cash received from exercise of stock options	$	14,844	$	7,974	$	2,517
Tax benefit from stock option exercises	$	4,567	$	4,288	$	1,680

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

	Number of Units	Weighted Average Contractual Life (Years)	Aggregate Intrinsic Value
Non-vested at December 31, 2011	—
Granted	37,310
Vested	—
Forfeited	—
Non-vested and expected to vest at December 31, 2012	37,310	1.0	$	2,273

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

	Year ended December 31,
	2012		2011		2010
Stock compensation expense	$	5,563	$	4,016	$	3,471
Tax benefit from stock-based compensation cost	1,922		1,376		1,153
Indirect tax benefit	209		785		438

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

	Year ended December 31,
	2012			2011			2010
Number of options granted	228,328			290,000			243,000
Grant date fair value of options granted (in thousands)	$	3,158		$	4,090		$	2,474
Weighted average assumptions for stock option valuation:
Expected term (years)	4.7			5.0			3.4
Expected stock price volatility	33.6		%	34.5		%	40.2		%
Risk-free interest rate	0.7		%	1.7		%	0.8		%
Expected dividend yield	—		%	—		%	—		%
Weighted average grant price per option	$	47.12		$	43.27		$	34.70
Weighted average grant date fair value per option	$	13.83		$	14.10		$	10.18

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, 2012 is as follows:

	Shares		Weighted Average Exercise Price Per Share		Weighted Average Contractual Life (Years)	Aggregate Intrinsic Value
Outstanding at December 31, 2011	2,745,428		$	33.28
Granted	228,328		$	47.12
Exercised	(526,040	)	$	28.22
Forfeited or expired	(2,963	)	$	34.12
Outstanding at December 31, 2012	2,444,753		$	35.66	4.7	$	61,778
Exercisable at December 31, 2012	1,670,325		$	34.66	3.5	$	43,873
Vested or expected to vest, December 31, 2012	2,444,753		$	35.66	4.7	$	61,778

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

	Year ended December 31,
	2012			2011			2010
ESPP shares purchased by employees	61,004			57,643			53,739
Intrinsic value of ESPP purchases (in thousands)	$	913		$	530		$	278
Weighted average assumptions for ESPP valuation:
Expected term (in years)	0.5			0.5			0.5
Expected stock price volatility	23.6		%	26.0		%	26.5		%
Risk-free interest rate	0.1		%	0.4		%	0.2		%
Expected dividend yield	—		%	—		%	—		%