Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified							3 Months Ended
	Mar. 31, 2012 6.50% Senior Notes [Member]	Dec. 31, 2011 6.50% Senior Notes [Member]	Mar. 31, 2012 6.625% Senior Notes [Member]	Dec. 31, 2011 6.625% Senior Notes [Member]	Mar. 31, 2012 Convertible Debt [Member]	Dec. 31, 2011 Convertible Debt [Member]	Mar. 31, 2012 Repayment of Debt [Member] Convertible Debt [Member]
Long-term debt
Debt Instrument, Face Amount	$ 350.0		$ 350.0
Interest rate on notes (as a percent)	6.50%	6.50%	6.625%	6.625%	3.50%	3.50%
Extinguishment of Debt, Amount							$ 281.3