Repurchases Of Common Stock (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Repurchases Of Common Stock [Abstract]
Shares repurchased	386,000	886,000	1,038,000	2,183,000
Total cost of shares repurchased	$ 36,146,000	$ 67,597,000	$ 91,152,000	$ 166,016,000
Average cost per share	$ 93.76	$ 76.27	$ 87.82	$ 76.04
Shares acquired through employee surrenders			51,484	54,940
Cost of shares acquired through employee surrenders			$ 4,500,000	$ 4,300,000