Debt (Convertible Debentures) (Details) (USD $)			12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 5.75% Junior Subordinated Convertible Debentures [Member]	Dec. 31, 2009 5.75% Junior Subordinated Convertible Debentures [Member]	Dec. 31, 2010 4.875% Unsecured Senior Notes [Member]	Dec. 31, 2009 4.875% Unsecured Senior Notes [Member]
Debt Instrument
Aggregate principal amount convertible debentures			$ 125,000,000			$ 250,000,000
Debt Instrument, Interest Rate, Stated Percentage			5.75%			4.875%
Terms of exchange offer				1,020		1,000
Unsecured debt, principal amount of debt extinguished						122,500,000
Maturity date			Sep. 15, 2029		Dec. 15, 2009
Liability component of convertible debt recognized at issuance				56,300,000
Fair value of convertible debt			206,800,000
Deferred tax impact on convertible debt	136,500,000	101,000,000		32,700,000
Junior subordinated convertible debentures convertible conversion price			$ 12.07
Junior subordinated convertible debentures convertible equity instruments in conversion			82.82
Debt Instrument, Convertible, Terms of Conversion Feature			1000
Percent Closing Price Must Be Of Conversion Price For Minimum 20 Days For Company To Reedeem Convertible Debt			150.00%
Percent Of Debt Converted To Equity			100.00%
Contingent Interest Component, Maxiumum			0.75%
Debt Instrument, Convertible, If-converted Value in Excess of Principal			$ 171,500,000