Stock Compensation Plans (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Stock Compensation Plans [Abstract]
Number of stock compensation plans	2
Compensation Expense [Abstract]
Share-based compensation expense	$ 1,619,000	$ 871,000
Tax benefit	(599,000)	(322,000)
Stock-based compensation expense, net of tax	1,020,000	549,000
Restricted Stock [Member] | Granted to Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	2,600,000
Weighted-average period of cost recognition (in years)	2.4
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, minimum (in years)	2
Vesting period, maximum (in years)	4
Expiration term (in years)	10
Unrecognized compensation expense	11,200,000
Weighted-average period of cost recognition (in years)	2.19
Valuation Assumptions [Abstract]
Expected Dividend Yield (in hundredths)		0.80%
Expected stock price volatility, minimum (in hundredths)		48.60%
Expected stock price volatility, maximum (in hundredths)		57.60%
Risk free interest rate, minimum (in hundredths)		0.86%
Risk free interest rate, maximum (in hundredths)		2.39%
Expected life options, minimum (in years)		2
Expected life options, maximum (in years)		5
Weighted-average fair value per share at grant date (in dollars per share)		$ 24.31
Stock Options, Shares [Roll Forward]
Outstanding, beginning of period (in shares)	1,504,311
Granted (in shares)	0
Exercised (in shares)	(50,051)
Forfeited or expired (in shares)	(6,750)
Outstanding, end of period (in shares)	1,447,510
Exercisable, end of period (in shares)	702,437
Weighted-Average Exercise Price [Abstract]
Outstanding, beginning of period (in dollars per share)	$ 42.26
Granted (in dollars per share)	$ 0
Exercised (in dollars per share)	$ 30.64
Forfeited or expired (in dollars per share)	$ 42.46
Outstanding, end of period (in dollars per share)	$ 42.66
Exercisable, end of period (in dollars per share)	$ 34.91
Weighted-Average Remaining Contractual Term [Abstract]
Outstanding, end of period (in years)	7.7
Exercisable, end of period (in years)	6.6
Aggregate Intrinsic Value [Abstract]
Outstanding, end of period	55,196,000
Exercisable, end of period	32,216,000
Intrinsic value of stock options exercised	$ 2,500,000
Stock Options [Member] | Granted to Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration term (in years)	10