Earnings Per Share, Other Disclosures (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended		12 Months Ended	3 Months Ended
	Apr. 19, 2013	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 Warrant Transactions	Apr. 15, 2013 Warrant Transactions
Potential dilutive effect of options and Warrants
Options outstanding to purchase common shares		20,791		20,791
Average exercise price per share		$ 80.01		$ 80.01
Potential dilutive effect of options outstanding		0		0
Number of common shares underlying the Warrants outstanding					3,600,000
Average exercise price of common shares underlying Warrants					61.25	61.19
Potential dilutive effect of shares underlying the Warrants					91,779
Dividends
Cash dividends paid		$ 5.9	$ 4.9
Cash dividends paid per share		$ 0.30	$ 0.25
Treasury Stock, Number of Shares and Restriction Disclosures [Abstract]
Common share amount available for additional share repurchase	92.8	30.7		46.9
Repurchase of common stock	210,835	259,596
Weighted-average price per share of common stock repurchased	$ 60.94	$ 62.62
Repurchase of common stock		$ 16.2