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Income Taxes (Narrative) (Details) (USD $)
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12 Months Ended | ||
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Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2012
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| Operating Loss Carryforwards [Line Items] | |||
| Alternative minimum tax credits | $ 24,053,000us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsAlternativeMinimumTax | $ 7,968,000us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsAlternativeMinimumTax | $ 1,643,000us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsAlternativeMinimumTax |
| Foreign tax credit carryforwards | 2,074,000us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsForeign | 2,074,000us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsForeign | 2,074,000us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsForeign |
| Valuation allowance of deferred tax assets | 3,145,000us-gaap_DeferredTaxAssetsValuationAllowance | 4,743,000us-gaap_DeferredTaxAssetsValuationAllowance | 4,629,000us-gaap_DeferredTaxAssetsValuationAllowance |
| Change in deferred tax asset valuation | 0us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance | (9,792,000)us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance | |
| Federal and state income taxes payable | 17,700,000us-gaap_TaxesPayableCurrentAndNoncurrent | 11,000,000us-gaap_TaxesPayableCurrentAndNoncurrent | |
| Diamondback [Member] | |||
| Operating Loss Carryforwards [Line Items] | |||
| Taxable gain on contribution |
203,300,000gpor_TaxableGainOnContributionOfOilAndGasProperties / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |
61,900,000gpor_TaxableGainOnContributionOfOilAndGasProperties / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |
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| Change in deferred tax asset valuation |
79,400,000us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |
0us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |
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| Deferred tax expense |
35,700,000us-gaap_DeferredIncomeTaxExpenseBenefit / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |
9,800,000us-gaap_DeferredIncomeTaxExpenseBenefit / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |
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| Deferred Other Tax Expense (Benefit) |
25,600,000us-gaap_DeferredOtherTaxExpenseBenefit / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |
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| Gain from sale of equity investment |
120,000,000us-gaap_GainLossOnSaleOfEquityInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |
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| Current tax expense |
13,200,000us-gaap_CurrentIncomeTaxExpenseBenefit / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |
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| Federal [Member] | |||
| Operating Loss Carryforwards [Line Items] | |||
| Net operating loss carryforward |
3,100,000us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_InternalRevenueServiceIRSMember |
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| Louisiana [Member] | |||
| Operating Loss Carryforwards [Line Items] | |||
| Net operating loss carryforward |
50,500,000us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |
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| Blackhawk Midstream LLC [Member] | |||
| Operating Loss Carryforwards [Line Items] | |||
| Change in deferred tax asset valuation |
32,300,000us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_BlackhawkMidstreamLlcMember |
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| Gain from sale of equity investment |
$ 83,700,000us-gaap_GainLossOnSaleOfEquityInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_BlackhawkMidstreamLlcMember |
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- Definition
Taxable Gain On Contribution Of Oil And Gas Properties No definition available.
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- Definition
Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of other deferred income tax expense (benefit) pertaining to income (loss) from continuing operations. For example, but not limited to, acquisition-date income tax benefits or expenses recognized from changes in the acquirer's valuation allowance for its previously existing deferred tax assets resulting from a business combination and adjustments to beginning-of-year balance of a valuation allowance because of a change in circumstance causing a change in judgment about the realizability of the related deferred tax asset in future periods. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible alternative minimum tax credit carryforwards. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible foreign tax credit carryforwards. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The difference between the carrying value and the sale price of equity securities, not separately or otherwise categorized as trading or available-for-sale. This element includes investments in which the entity holds a small ownership stake (generally, less than 20% of the shares outstanding) and cannot exert significant influence. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Carrying value as of the balance sheet date of obligations incurred and payable for statutory income, sales, use, payroll, excise, real, property and other taxes. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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