Repurchases Of Common Stock (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Repurchases Of Common Stock [Abstract]
Shares repurchased	333,000	538,000
Total cost of shares repurchased	$ 27,630,000	$ 39,940,000
Average cost per share	$ 82.85	$ 74.21
Shares acquired through employee surrenders	48,574	51,407
Cost of shares acquired through employee surrenders	$ 4,200,000	$ 4,000,000