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Income Taxes--Components of Deferred Tax Assets and Liabilities (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Income Tax Disclosure [Abstract]    
Asset retirement obligations $ 12,988us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAssetRetirementObligations $ 8,777us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAssetRetirementObligations
Accrued expenses, allowance and other 15,057us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsOther 14,508us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsOther
Derivative instruments 0us-gaap_DeferredTaxAssetsDerivativeInstruments 129us-gaap_DeferredTaxAssetsDerivativeInstruments
Net operating loss carryforwards - Federal 121,556us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic 124,855us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic
Net operating loss carryforwards - State 15,052us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal 13,350us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal
Statutory depletion carryforwards 3,833us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration 2,867us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration
Alternative minimum tax credit carryforwards 308us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsAlternativeMinimumTax 308us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsAlternativeMinimumTax
Deferred tax assets, gross 168,794us-gaap_DeferredTaxAssetsGross 164,794us-gaap_DeferredTaxAssetsGross
Less valuation allowance (10,499)us-gaap_DeferredTaxAssetsValuationAllowance (10,385)us-gaap_DeferredTaxAssetsValuationAllowance
Deferred tax asset 158,295us-gaap_DeferredTaxAssetsNet 154,409us-gaap_DeferredTaxAssetsNet
Derivative instruments (88,910)us-gaap_DeferredTaxLiabilitiesDerivatives 0us-gaap_DeferredTaxLiabilitiesDerivatives
Property and equipment (245,629)us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment (206,799)us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment
Inventories (1,243)us-gaap_DeferredTaxLiabilitiesDeferredExpenseCapitalizedInventoryCosts (1,205)us-gaap_DeferredTaxLiabilitiesDeferredExpenseCapitalizedInventoryCosts
Deferred tax liability (335,782)us-gaap_DeferredIncomeTaxLiabilities (208,004)us-gaap_DeferredIncomeTaxLiabilities
Net deferred tax liability (177,487)us-gaap_DeferredTaxLiabilities (53,595)us-gaap_DeferredTaxLiabilities
Less net current deferred tax asset (liability) (60,728)us-gaap_DeferredTaxAssetsLiabilitiesNetCurrent 9,260us-gaap_DeferredTaxAssetsLiabilitiesNetCurrent
Long-term deferred tax liability $ (116,759)us-gaap_DeferredTaxLiabilitiesNoncurrent $ (62,855)us-gaap_DeferredTaxLiabilitiesNoncurrent