Debt (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended														0 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 7.875% notes payable, due 2014	Dec. 31, 2010 7.875% notes payable, due 2014	May 18, 2009 7.875% notes payable, due 2014	Dec. 31, 2011 8.875% notes payable, due 2019	Dec. 31, 2010 8.875% notes payable, due 2019	May 18, 2009 8.875% notes payable, due 2019	Dec. 31, 2011 6.05% notes payable, due 2036	Dec. 31, 2010 6.05% notes payable, due 2036	Dec. 05, 2006 6.05% notes payable, due 2036	Oct. 16, 2006 6.05% notes payable, due 2036	May 18, 2009 7.875% notes payable, due 2014 and 8.875% notes payable, due 2019	Aug. 15, 2009 8.2% notes payable, due 2009
Long-Term Debt
Long-term debt interest rate (as a percent)				7.875%	7.875%	7.875%	8.875%	8.875%	8.875%	6.05%	6.05%	6.05%	6.05%
Long-term debt issued						$ 400.0			$ 350.0			$ 100.0	$ 500.0	$ 750.0
Principal repayments of long-term debt	$ 12.2	$ 11.1	$ 468.2												$ 440.9