Debt 7.75% Senior Subordinated Notes (Details) (USD $)	Dec. 31, 2010	Dec. 31, 2011 7.75% Senior Subordinated Notes, Due 2020 [Member]	Dec. 31, 2011 Initial 7.75% Swap Agreement [Member] 7.75% Senior Subordinated Notes, Due 2020 [Member]	Dec. 31, 2011 Additional 7.75% swap agreement [Member] 7.75% Senior Subordinated Notes, Due 2020 [Member]
Debt Instrument, Face Amount		$ 550,000,000
Debt Instrument, Interest Rate, Stated Percentage		7.75%
Debt Instrument, Initial Face Value		400,000,000
Deferred Finance Costs, Gross		12,600,000
Offering Of Additional Senior Subordinated Notes Aggregate Principal Amount		150,000,000
Derivative, Variable Interest Rate		5.07%	3.87%	5.32%
Derivative, Fair Value, Net	$ (4,290,000)