Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Taxes
Effective tax rate of provision for income taxes	39.30%	39.30%	31.50%
Net long term deferred income tax liabilities	$ 1,586,798,000	$ 1,130,292,000
Net current deferred income tax liability	194,163,000	44,089,000
Paid in state income taxes	800,000	400,000
Alternative minimum tax payments	3,400,000	14,000,000
Operating Loss Carryforwards	878,200,000
Net operating loss carryforwards expire between 2027 and 2031	2027 through 2031
Alternative minimum tax credit carryforward	73,516,000	70,138,000
Statutory depletion carryforward	13,000,000
Windfalls included in net operating loss carryforwards but not reflected in deferred tax assets	110,300,000
Income tax years 2009-2011	2009 to 2011
Valuation allowance, amount	$ 2,000,000	$ 500,000.0