Long-Term Debt (Details) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
6.50% Senior Notes [Member]
Long-term debt
Debt Instrument, Face Amount	$ 350.0
Interest rate on notes (as a percent)	6.50%	6.50%
6.625% Senior Notes [Member]
Long-term debt
Debt Instrument, Face Amount	350.0
Interest rate on notes (as a percent)	6.625%	6.625%
Convertible Debt [Member]
Long-term debt
Interest rate on notes (as a percent)	3.50%	3.50%
Stock Issued During Period, Shares, Conversion of Convertible Securities	864,106
cash paid for redemption of convertible debt	6.2
Repayments of Long-term Debt	281.3
6.50% Senior Notes due 2023 [Member]
Long-term debt
Debt Instrument, Face Amount	400.0
Interest rate on notes (as a percent)	6.50%
Proceeds from Debt, Net of Issuance Costs	392.3
Deferred Finance Costs, Gross	7.7
Debt Instrument Future Redemption Amount As Percentage Of Principal	35.00%
Debt Instrument Future Redemption Price As Percentageof Principal First Through Third Year	106.50%
Senior Notes due 2023 Redemption Schedule [Abstract]
Debt Instrument, Future Redemption Price as Percentage of Principal, Year 5	103.25%
Debt Instrument Future Redemption Price as Percentage of Principal, Year 6	102.167%
Debt Instrument, Future Redemption Price as Percentage of Principal, Year 7	101.083%
Debt Instrument, Future Redemption Price as Percentage of Principal, Year 8 and Thereafter	100.00%
Debt Instrument, Covenant Compliance, Dividends Excluded From Computation	$ 6.5
Debt Instrument, Additional Interest Rate Maximum for Failure to File Exchange Offer or Ineffective Shelf Registration Statement	1.00%
Debt Instrument Future Redemption Price As Percentage Of Principal, First Five Year	100.00%