Long-Term Debt (Details 2) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jan. 31, 2012 Term Loan maturing in 2016	Jan. 31, 2012 7 3/8% senior notes, due 2012	Dec. 31, 2011 7 3/8% senior notes, due 2012	Dec. 31, 2010 7 3/8% senior notes, due 2012
Long Term Debt
Additional borrowings				$ 275,000,000
Repayments of Debt	7,740,000	346,963,000	1,690,557,000		279,700,000
Carrying amount of long-term debt, including current maturities	2,380,100,000	2,386,821,000				700,000,000	700,000,000
Note stated interest rate (as a percent)					7.375%	7.375%	7.375%
Maturities of outstanding debt
2012	444,078,000
2013	16,770,000
2014	318,111,000
2015	544,421,000
2016	682,461,000			158,000,000
Thereafter	374,259,000
Total debt	2,380,100,000	2,386,821,000				700,000,000	700,000,000
Interest costs
Interest costs incurred	178,700,000	177,200,000	162,300,000
Interest costs incurred capitalized	1,700,000	7,000,000	20,900,000
Cash paid for interest	$ 171,800,000	$ 162,400,000	$ 156,200,000