Stock Compensation Plans (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Stock Compensation Plans [Abstract]
Number of stock compensation plans	2		2
Compensation Expense [Abstract]
Share-based compensation expense	$ 1,797,000	$ 2,001,000	$ 3,416,000	$ 2,873,000
Tax benefit	(665,000)	(740,000)	(1,264,000)	(1,063,000)
Stock-based compensation expense, net of tax	1,132,000	1,261,000	2,152,000	1,810,000
Restricted Stock [Member] | Granted to Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	3,300,000		3,300,000
Weighted-average period of cost recognition (in years)			1.9
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	9,900,000		9,900,000
Weighted-average period of cost recognition (in years)			1.94
Valuation Assumptions [Abstract]
Expected dividend yield, maximum (in hundredths)				0.60%
Expected dividend yield, minimum (in hundredths)				0.80%
Expected stock price volatility, minimum (in hundredths)				40.50%
Expected stock price volatility, maximum (in hundredths)				57.90%
Risk free interest rate, minimum (in hundredths)				0.28%
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)				$ 27.36
Stock Options, Shares [Roll Forward]
Outstanding, beginning of period (in shares)			1,504,311
Granted (in shares)			0
Exercised (in shares)			(58,051)
Forfeited or expired (in shares)			(7,974)
Outstanding, end of period (in shares)		1,438,286		1,438,286
Exercisable, end of period (in shares)		707,155		707,155
Weighted-Average Exercise Price [Abstract]
Outstanding, beginning of period (in dollars per share)			$ 42.26
Granted (in dollars per share)	$ 0		$ 0
Exercised (in dollars per share)	$ 28.14		$ 28.14
Forfeited or expired (in dollars per share)			$ 44.16
Outstanding, end of period (in dollars per share)		$ 42.82		$ 42.82
Exercisable, end of period (in dollars per share)		$ 35.72		$ 35.72
Weighted-Average Remaining Contractual Term [Abstract]
Outstanding, end of period (in years)		7.5		7.5
Exercisable, end of period (in years)			6.4
Aggregate Intrinsic Value [Abstract]
Outstanding, end of period		20,179,000		20,179,000
Exercisable, end of period		14,617,000		14,617,000
Intrinsic value of stock options exercised			$ 3,000,000
Stock Options [Member] | Granted to Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration term (in years)			10