Common Stock Repurchase Programs (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended				48 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2011	Oct. 31, 2011	May 31, 2010	Oct. 31, 2008	May 31, 2008
Common Stock Repurchase Programs
Number of Shares Authorized	12,000,000				12,000,000	2,000,000	2,000,000	6,000,000	2,000,000
Total Number of Shares Repurchased	2,243,000	1,670,000	1,380,000	4,662,000	9,955,000
Cost	$ 51,582	$ 35,881	$ 14,578	$ 61,572	$ 163,613
Average Price Paid per Share for Shares Repurchased	$ 23.00	$ 21.48	$ 10.57	$ 13.21	$ 16.44
Remaining number of shares authorized for repurchase by the Board	2,000,000				2,000,000