Share Repurchase Programs (Details) (USD $)	12 Months Ended					12 Months Ended			12 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2010 February 2010 Discretionary Share Repurchase Program [Member]	Feb. 28, 2010 February 2010 Discretionary Share Repurchase Program [Member]	Dec. 31, 2011 December 2009 Anti-Dilutive Share Repurchase Program [Member]	Dec. 31, 2010 December 2009 Anti-Dilutive Share Repurchase Program [Member]	Dec. 31, 2009 December 2009 Anti-Dilutive Share Repurchase Program [Member]	Dec. 31, 2009 December 2007 Discretionary Share Repurchase Program [Member]	Dec. 31, 2007 December 2007 Discretionary Share Repurchase Program [Member]	Dec. 31, 2009 December 2007 Anti Dilutive Share Repurchase Program [Member]	Dec. 31, 2007 Anti-dilutive share repurchase program [Member]
Share Repurchase Programs (Textual) [Abstract]
Discretionary Share Repurchase Program Authorization					$ 100,000,000					$ 300,000,000
Maximum period of discretionary share repurchase program					2 years					2 years
Repurchased and retired shares				2,420,390		1,175,783	561,656		2,348,909		377,372
Aggregate cost of repurchased and retired	$ 59,102,000	$ 123,170,000	$ 116,281,000	$ 100,000,000		$ 59,000,000	$ 23,000,000		$ 100,000,000		$ 16,000,000
Maximum number of share repurchases authorization								2,000,000				2,000,000