Repurchases of Outstanding Securities (Details) (USD $)	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Repurchases of Outstanding Securities (Details) [Abstract]
Authorized aggregate amount		$ 1,000,000,000
Total number of shares repurchased since inception of our stock repurchase program (shares)		30,189,738		29,322,753
Aggregate purchase price of shares repurchased since inception of our stock repurchase program		745,600,000		715,500,000
Number of shares repurchased (shares)	378,254	866,985
Purchase price of shares repurchased	$ 13,600,000	$ 30,121,000	$ 164,168,000