Stock Option Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stock Option Plans [Abstract]
Number of stock compensation plans	2
Compensation Expense [Abstract]
Share-based compensation expense	$ 5,310,000	$ 4,627,000	$ 2,943,000
Tax benefit	(1,964,000)	(1,712,000)	(1,089,000)
Stock-based compensation expense, net of tax	3,346,000	2,915,000	1,854,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted (in shares)	57,300
Vesting period of granted stock (in years)	3Y
Fair value of restricted stock granted (in dollars per share)	$ 57.40
Stock-based compensation, additional disclosures [Abstract]
Unrecognized compensation expense	2,900,000
Weighted-average period of cost recognition (in years)	2.7
Stock Options [Member]
Valuation Assumptions [Abstract]
Expected dividend yield, minimum (in hundredths)	0.60%	0.94%	0.87%
Expected dividend yield, maximum (in hundredths)	0.80%	1.60%	1.40%
Expected stock price volatility, minimum (in hundredths)	48.10%	51.20%	23.40%
Expected stock price volatility, maximum (in hundredths)	57.90%	57.80%	28.15%
Risk free interest rate, minimum (in hundredths)	0.28%	0.53%	0.55%
Risk free interest rate, maximum (in hundredths)	2.39%	2.96%	1.37%
Expected life options, minimum (in years)	3	2	3
Expected life options, maximum (in years)	4	6	7
Weighted-average fair value per share at grant date (in dollars per share)	$ 26.29	$ 17.05	$ 10.13
Stock Options, Shares [Roll Forward]
Outstanding, beginning of period (in shares)	1,321,637
Granted (in shares)	434,948
Exercised (in shares)	(188,649)
Forfeited or expired (in shares)	(63,625)
Outstanding, end of period (in shares)	1,504,311	1,321,637
Exercisable, end of period (in shares)	666,613
Weighted-Average Exercise Price [Abstract]
Outstanding, beginning of period (in dollars per share)	$ 33.26
Granted (in dollars per share)	$ 62.69
Exercised (in dollars per share)	$ 27.37
Forfeited or expired (in dollars per share)	$ 39.36
Outstanding, end of period (in dollars per share)	$ 42.26	$ 33.26
Exercisable, end of period (in dollars per share)	$ 34.53
Weighted-Average Remaining Contractual Term [Abstract]
Outstanding, end of period (in years)	7.9
Exercisable, end of period (in years)	6.8
Aggregate Intrinsic Value [Abstract]
Outstanding, end of period	38,733,000
Exercisable, end of period	22,419,000
Stock-based compensation, additional disclosures [Abstract]
Unrecognized compensation expense	12,700,000
Weighted-average period of cost recognition (in years)	2.3
Intrinsic value of stock options exercised	$ 9,200,000	$ 11,400,000	$ 1,000,000
Stock Options [Member] | Granted to Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration term (in years)	10Y
Stock Options [Member] | Granted to Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, minimum (in years)	2Y
Vesting period, maximum (in years)	4Y
Expiration term (in years)	10Y