Stock Compensation Plans (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	May 31, 2013
Stock Compensation Plans [Abstract]
Number of stock compensation plans	2
Compensation Expense [Abstract]
Total stock-based compensation expense	$ 2,573,000	$ 1,619,000
Tax benefit	(952,000)	(599,000)
Stock-based compensation expense, net of tax	1,621,000	1,020,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, minimum (in years)	P2Y
Vesting period, maximum (in years)	P4Y
Compensation Expense [Abstract]
Total stock-based compensation expense	1,212,000	1,331,000
Valuation Assumptions [Abstract]
Expected dividend yield, maximum (in hundredths)	1.02%
Expected stock price volatility, minimum (in hundredths)	46.40%
Expected stock price volatility, maximum (in hundredths)	53.00%
Risk free interest rate, minimum (in hundredths)	0.27%
Risk free interest rate, maximum (in hundredths)	0.60%
Expected life options, minimum (in years)	2
Expected life options, maximum (in years)	4
Weighted-average fair value per share at grant date (in dollars per share)	$ 18.24
Stock Options, Shares [Roll Forward]
Outstanding, beginning of period (in shares)	1,625,327
Granted (in shares)	10,500	0
Exercised (in shares)	(30,182)
Forfeited or expired (in shares)	(15,791)
Outstanding, end of period (in shares)	1,589,854
Exercisable, end of period (in shares)	954,735
Weighted-Average Exercise Price [Abstract]
Outstanding, beginning of period (in dollars per share)	$ 43.96
Granted (in dollars per share)	$ 62.26
Exercised (in dollars per share)	$ 36.63
Forfeited or expired (in dollars per share)	$ 57.64
Outstanding, end of period (in dollars per share)	$ 44.08
Exercisable, end of period (in dollars per share)	$ 38.54
Weighted-Average Remaining Contractual Term [Abstract]
Outstanding, end of period (in years)	7.1
Exercisable, end of period (in years)	6.2
Aggregate Intrinsic Value [Abstract]
Outstanding, end of period	36,657,000
Exercisable, end of period	27,340,000
Unrecognized compensation expense	4,600,000
Weighted-average period of cost recognition (in years)	1.83
Intrinsic value of stock options exercised	900,000
Stock Options [Member] | Granted to Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration term (in years)	P10Y
Stock Options [Member] | Granted to Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration term (in years)	P10Y
Restricted Stock Awards and Units [Member]
Compensation Expense [Abstract]
Total stock-based compensation expense	871,000	288,000
Aggregate Intrinsic Value [Abstract]
Unrecognized compensation expense	4,300,000
Weighted-average period of cost recognition (in years)	1.67
Number of Awards [Abstract]
Outstanding, beginning of period (in shares)	109,907
Granted (in shares)	0
Vested (in shares)	0
Forfeited (in shares)	0
Outstanding, end of period (in shares)	109,907
Weighted-Average Grant Date Fair Value [Roll Forward]
Outstanding, beginning of period (in dollars per share)	$ 60.13
Granted (in dollars per share)	$ 0
Vested (in dollars per share)	$ 0
Forfeited (in dollars per share)	$ 0
Outstanding, end of period (in dollars per share)	$ 60.13
Performance Shares [Member]
Compensation Expense [Abstract]
Total stock-based compensation expense	490,000	0
Aggregate Intrinsic Value [Abstract]
Unrecognized compensation expense	$ 2,900,000
Weighted-average period of cost recognition (in years)	1.28
Number of Awards [Abstract]
Outstanding, beginning of period (in shares)	67,155		67,155
Granted (in shares)	0
Forfeited (in shares)	0
Outstanding, end of period (in shares)			67,155
Weighted-Average Grant Date Fair Value [Roll Forward]
Outstanding, end of period (in dollars per share)	$ 58.66