Earnings Per Share, Textuals (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Potential dilutive effect of options and Warrants
Options outstanding to purchase common shares	20,791	20,791		20,791
Average exercise price per share	$ 80.01	$ 80.01		$ 80.01
Dividends
Cash dividends paid		$ 12.8	$ 11.6
Cash dividends paid per share	$ 0.35	$ 0.70	$ 0.60
Treasury Stock, Number of Shares and Restriction Disclosures [Abstract]
Repurchase of common stock		346,781	654,277
Weighted-average price per share of common stock repurchased		$ 69.25	$ 61.95
Repurchase of common stock, total cost		24.0	40.5
Common share amount available for additional share repurchase		$ 93.6		$ 117.6
Warrant Transactions
Potential dilutive effect of options and Warrants
Number of common shares underlying the Warrants outstanding	3,600,000	3,600,000	3,600,000
Average exercise price of common shares underlying Warrants	60.89	60.89	61.19