Treasury Stock (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Equity, Class of Treasury Stock [Line Items]
Treasury stock purchase plan	$ 40,000,000
Treasury Stock, Value	(11,956,000)	(28,648,000)	(20,441,000)
Treasury Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury Stock, Value	12,000,000
Purchase plan 2010 [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury Stock, Value	11,900,000
Purchase Plan 2008 [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury Stock, Value	$ 100,000