Income Taxes (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Gross long term deferred income tax liabilities	$ 1,049,138,000	$ 1,586,798,000
Effective tax rate of provision for income taxes	38.50%	39.30%	39.30%
Net current deferred income tax liability	106,123,000	194,163,000
Paid In State Income Taxes	800,000	800,000
Alternative minimum tax payments		3,400,000
Operating Loss Carryforwards	701,400,000
Net operating loss carryforwards expire between 2027 and 2031	2027 through 2032
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	89,016,000	73,516,000
Statutory depletion carryforward	13,600,000
Windfalls Included In Net Operating Loss Carryforwards But Not Reflected In Deferred Tax Assets	128,300,000
Net long-term deferred tax liabilities	1,045,500,000
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Net operating loss carryforwards expire between 2027 and 2031	2030 through 2032
Valuation Allowance, Amount		2,000,000
Net operating loss carryforward	$ 15,900,000