Long-Term Debt (Details) (USD $)	9 Months Ended						9 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 6.50% Senior Notes [Member]	Dec. 31, 2011 6.50% Senior Notes [Member]	Sep. 30, 2012 6.625% Senior Notes [Member]	Dec. 31, 2011 6.625% Senior Notes [Member]	Sep. 30, 2012 Convertible Debt [Member]	Dec. 31, 2011 Convertible Debt [Member]	Sep. 30, 2012 6.50% Senior Notes due 2023 [Member]
Long-term debt
Debt Instrument, Face Amount			$ 350,000,000		$ 350,000,000				$ 400,000,000
Interest rate on notes (as a percent)			6.50%	6.50%	6.625%	6.625%	3.50%	3.50%	6.50%
Proceeds from Issuance of Long-term Debt	392,223,000	0							392,223,000
Stock Issued During Period, Shares, Conversion of Convertible Securities							864,106
Cash Paid For Redemption Of Convertible Debt							6,200,000
Repayments of Long-term Debt							281,300,000
Deferred Finance Costs, Gross									7,800,000
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									$ 6,500,000
Debt Instrument Future Redemption Price As Percentage Of Principal, First Five Year									100.00%