Earnings Per Share, Other Disclosures (Details) (USD $)	3 Months Ended		12 Months Ended
	Dec. 31, 2012	Mar. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Warrant Transactions	Dec. 31, 2011 Warrant Transactions	Dec. 31, 2010 Warrant Transactions	Feb. 15, 2013 Warrant Transactions	Mar. 30, 2010 Warrant Transactions
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
Potential dilutive effect of shares underlying the options			0	0	0
Number of common shares underlying the Warrants outstanding						3,600,000				3,600,000
Average exercise price of common shares underlying warrants						61.31			61.25
Potential dilutive effect of shares underlying the Warrants						0	0	0
Dividends
Payment of cash dividends to stockholders			$ 19,600,000	$ 18,900,000	$ 19,000,000
Payment of quarterly cash dividends	$ 0.25		$ 1.00	$ 0.96	$ 0.96
Treasury Stock, Number of Shares and Restriction Disclosures [Abstract]
Common shares available for additional share repurchase			46,900,000
Repurchase of common shares authorized by Board			0	0	0
Repurchase of common shares pursuant to a separate authorization from the Board, value		$ 44,200,000
Repurchase of common shares pursuant to a separate authorization from the Board, shares		1,151,900