Subsequent Events (Details) (USD $)	6 Months Ended		12 Months Ended	0 Months Ended	6 Months Ended	0 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jul. 15, 2014 Subsequent Event	Jun. 30, 2014 Convertible Notes	Jul. 15, 2014 Convertible Notes Subsequent Event	Jun. 30, 2014 Call Options	Jul. 15, 2014 Call Options Subsequent Event	Jun. 30, 2014 Warrants	Jun. 30, 2013 Warrants	Jul. 15, 2014 Warrants Subsequent Event
Subsequent Event [Line Items]
Cash dividend declared per common share				$ 0.35
Cash dividends declared				$ 6,300,000
Conversion rate of common stock shares per $1,000 of principal amount					20.8549	20.8862
Principal amount in conversion feature					1,000	1,000
Conversion price per share of note					$ 47.95	$ 47.88
Exercise price per share of Call Options							$ 47.95	$ 47.88
Exercise price per share of Warrants									60.89	61.19	60.80
Repurchase of common stock, shares	346,781	654,277
Weighted-average price per share of common stock repurchased	$ 69.25	$ 61.95
Common share amount available for additional share repurchase	$ 93,600,000		$ 117,600,000