Share-Based Compensation (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 plan	Dec. 31, 2010	Dec. 31, 2009
Share-Based Compensation
Number of share-based compensation plans	1
Compensation cost recognized for share-based awards	$ 19,500,000	$ 16,700,000	$ 14,400,000
Total income tax benefit recognized for share-based compensation arrangements	8,100,000	7,000,000	6,000,000
Cash received from the exercise of stock options	5,089,000	23,764,000	2,236,000
Actual tax benefit realized for the tax deductions from stock option exercises	1,200,000	4,700,000
Share-based compensation
Shares available for future grants	1.4
Stock options
Share-based compensation
Minimum vesting period (in years)	4 years
Expiration period (in years)	P10Y
Share-based compensation, fair value
Volatility look back period (in years)	20
Weighted-average volatility (as a percent)	30.90%	31.41%	31.42%
Dividend yield (as a percent)	1.67%	0.73%	3.33%
Expected term (in years)	6.11	6.10	6.11
Risk-free interest rate (as a percent)	2.86%	2.91%	2.84%
Weighted-average grant-date fair values of options granted (in dollars per share)	$ 17.55	$ 16.82	$ 6.90
Total intrinsic values of options exercised	$ 2,800,000	$ 11,800,000	$ 900,000
Restricted stock
Share-based compensation
Minimum vesting period (in years)	3 years
Vesting Period for awards (in years)	5