Subsequent Events (Details) (USD $)	0 Months Ended	9 Months Ended	12 Months Ended	0 Months Ended	9 Months Ended	1 Months Ended
	Oct. 15, 2013	Sep. 30, 2013	Dec. 31, 2012	Oct. 15, 2013 Subsequent Event	Sep. 30, 2013 Convertible Notes	Oct. 22, 2013 Convertible Notes Subsequent Event	Oct. 22, 2013 Call Options	Sep. 30, 2013 Call Options	Sep. 30, 2013 Warrants	Sep. 30, 2012 Warrants	Oct. 22, 2013 Warrants Subsequent Event
Subsequent Events (Textuals) [Abstract]
Cash dividend declared per common share				$ 0.30
Cash dividends declared	$ 5,700,000
Conversion rate of common stock shares per $1,000 of principal amount					20.7714	20.7903
Principal amount in conversion feature					1,000	1,000
Conversion price per share of note					$ 48.14	$ 48.10
Exercise price per share of Call Options							$ 48.10	$ 48.14
Exercise price per share of Warrants									61.14	61.32	61.08
Repurchase of common stock, shares		707,077
Weighted-average price per share of common stock repurchased		$ 62.14
Common share amount available for additional share repurchase		$ 78,000,000	$ 46,900,000