Share-Based Compensation (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Equity stock-based compensation
Total share-based compensation expense included in net income	$ 4,200,000	$ 4,100,000	$ 8,500,000	$ 7,400,000
Income tax benefit related to stock-based compensation included in net income	1,200,000	1,400,000	2,600,000	2,500,000
Stock Option Awards
Equity stock-based compensation
Term of options (in years)			P10Y
Period of vesting (in years)			3 years
Assumptions used to measure the fair value of awards
Expected life (in years)			5.8	5.8
Risk-free interest rate (as a percent)			1.07%	2.76%
Expected volatility (as a percent)			33.33%	32.71%
Expected dividend yield (as a percent)			1.18%	1.17%
Stock option activity
Outstanding at the beginning of the period (in shares)			4,030
Granted (in shares)			460	438
Exercised (in shares)			(467)
Cancelled (in shares)			(18)
Outstanding at the end of the period (in shares)	4,005		4,005
Exercisable at the end of the period (in shares)	3,038		3,038
Share options, weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)			$ 30.29
Granted (in dollars per share)	$ 55.96		$ 55.96
Exercised (in dollars per share)	$ 26.35		$ 26.35
Cancelled (in dollars per share)			$ 40.07
Outstanding at the end of the period (in dollars per share)	$ 33.65		$ 33.65
Exercisable at the end of the period (in dollars per share)	$ 29.34		$ 29.34
Share options, aggregate intrinsic value, average remaining contractual life
Options outstanding average remaining contractual life (in years)	6.09		6.09
Options outstanding aggregate intrinsic value	66,503,000		66,503,000
Stock options exercisable average remaining contractual life (in years)			5.21
Stock options exercisable aggregate intrinsic value	61,327,000		61,327,000
Additional information pertaining to stock options
Cash received from exercise of stock options			13,000,000
Excess tax benefit realized from exercise of stock options			1,000,000
Unrecognized compensation cost	10,000,000		10,000,000
Weighted-average period for amortization of unrecognized compensation cost (in years)			1.5
Weighted-average grant date fair value of stock options granted (in dollars per share)	$ 16.56	$ 16.65	$ 16.16	$ 15.17
Total intrinsic value of stock options exercised	$ 3,058,000	$ 9,521,000	$ 14,055,000	$ 15,181,000