Stock Repurchases (Details Textual) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 2008 Share Repurchase Plan [Member]	Dec. 31, 2012 2008 Share Repurchase Plan [Member]	Dec. 31, 2008 2008 Share Repurchase Plan [Member]	Dec. 31, 2012 2012 Share Repurchase Plan [Member]
Equity, Class of Treasury Stock [Line Items]
Authorized amount for share repurchase				$ 400,000,000		$ 300,000,000	$ 300,000,000
Increase in authorized amount for share repurchase				100,000,000
Treasury stock purchases	57,300,000	123,000,000	153,700,000		50,100,000
Treasury stock purchases, shares					1,100,000
Remaining authorized amount for share repurchase					$ 71,200,000
Shares repurchased							0