Derivative Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended			1 Months Ended		1 Months Ended
	Sep. 30, 2009	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jun. 30, 2003 June 2003 Interest Rate Swap [Member]	Dec. 31, 2012 June 2003 Interest Rate Swap [Member]	Aug. 31, 2003 August 2003 Interest Rate Swap [Member]	Dec. 31, 2011 August 2003 Interest Rate Swap [Member]
Derivative [Line Items]
Interest rate swap agreements with underlying notional amounts of debt					$ 100		$ 50
Interest rate swap agreements, maturity date			May 31, 2011		May 31, 2011		May 31, 2011
Interest rate swap agreements, fixed rate						7.375%		7.375%
Principal amount of long-term debt repayments	43.2	88.1	306.8
Increases in interest expense			$ 1.9	$ 3.4