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Supplemental Information On Oil And Gas Exploration And Production Activities (Results of Operations for Producing Activities) (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Results of Operations for Oil and Gas Producing Activities [Line Items] |  |  |
Revenues | $ 670,762,000 us-gaap_ResultsOfOperationsRevenueFromOilAndGasProducingActivities | $ 262,225,000 us-gaap_ResultsOfOperationsRevenueFromOilAndGasProducingActivities | $ 248,601,000 us-gaap_ResultsOfOperationsRevenueFromOilAndGasProducingActivities
Production costs | (140,664,000)us-gaap_ResultsOfOperationsProductionOrLiftingCosts | (64,666,000)us-gaap_ResultsOfOperationsProductionOrLiftingCosts | (53,708,000)us-gaap_ResultsOfOperationsProductionOrLiftingCosts
Depletion | (263,946,000)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions | (118,118,000)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions | (90,230,000)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions
Results of operations, before income taxes | 266,152,000 us-gaap_ResultsOfOperationsIncomeBeforeIncomeTaxes | 79,441,000 us-gaap_ResultsOfOperationsIncomeBeforeIncomeTaxes | 104,663,000 us-gaap_ResultsOfOperationsIncomeBeforeIncomeTaxes
Current | 0 gpor_ResultsOfOperationsIncomeTaxExpenseCurrent | 0 gpor_ResultsOfOperationsIncomeTaxExpenseCurrent | 730,000 gpor_ResultsOfOperationsIncomeTaxExpenseCurrent
Deferred | 96,061,000 gpor_ResultsOfOperationsIncomeTaxExpenseDeferred | 49,447,000 gpor_ResultsOfOperationsIncomeTaxExpenseDeferred | 25,633,000 gpor_ResultsOfOperationsIncomeTaxExpenseDeferred
Income tax expense | 96,061,000 us-gaap_ResultsOfOperationsIncomeTaxExpense | 49,447,000 us-gaap_ResultsOfOperationsIncomeTaxExpense | 26,363,000 us-gaap_ResultsOfOperationsIncomeTaxExpense
Results of operations from producing activities | 170,091,000 us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts | 29,994,000 us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts | 78,300,000 us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts
Depletion per MCF of Gas Equivalent | 3.01 gpor_DepletionperMCFofGasEquivalent | 4.78 gpor_DepletionperMCFofGasEquivalent | 5.85 gpor_DepletionperMCFofGasEquivalent
Diamondback Energy, Inc [Member] |  |  |
Results of Operations for Oil and Gas Producing Activities [Line Items] |  |  |
Revenues | 0 us-gaap_ResultsOfOperationsRevenueFromOilAndGasProducingActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 14,976,000 us-gaap_ResultsOfOperationsRevenueFromOilAndGasProducingActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 16,042,000 us-gaap_ResultsOfOperationsRevenueFromOilAndGasProducingActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Production costs | 0 us-gaap_ResultsOfOperationsProductionOrLiftingCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (2,518,000)us-gaap_ResultsOfOperationsProductionOrLiftingCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (4,474,000)us-gaap_ResultsOfOperationsProductionOrLiftingCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Depletion | 0 us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (4,754,000)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (5,515,000)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Results of operations, before income taxes | 0 us-gaap_ResultsOfOperationsIncomeBeforeIncomeTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 7,704,000 us-gaap_ResultsOfOperationsIncomeBeforeIncomeTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 6,053,000 us-gaap_ResultsOfOperationsIncomeBeforeIncomeTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Income tax expense | 0 us-gaap_ResultsOfOperationsIncomeTaxExpense / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 2,286,000 us-gaap_ResultsOfOperationsIncomeTaxExpense / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 2,158,000 us-gaap_ResultsOfOperationsIncomeTaxExpense / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Results of operations from producing activities | 0 us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 5,418,000 us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 3,895,000 us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Grizzly Oil Sands ULC [Member] |  |  |
Results of Operations for Oil and Gas Producing Activities [Line Items] |  |  |
Revenues | 5,449,000 us-gaap_ResultsOfOperationsRevenueFromOilAndGasProducingActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_ResultsOfOperationsRevenueFromOilAndGasProducingActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_ResultsOfOperationsRevenueFromOilAndGasProducingActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Production costs | (10,113,000)us-gaap_ResultsOfOperationsProductionOrLiftingCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_ResultsOfOperationsProductionOrLiftingCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_ResultsOfOperationsProductionOrLiftingCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Depletion | (1,195,000)us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_ResultsOfOperationsDepreciationDepletionAndAmortizationAndValuationProvisions / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Results of operations, before income taxes | (5,859,000)us-gaap_ResultsOfOperationsIncomeBeforeIncomeTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_ResultsOfOperationsIncomeBeforeIncomeTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_ResultsOfOperationsIncomeBeforeIncomeTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Income tax expense | 0 us-gaap_ResultsOfOperationsIncomeTaxExpense / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_ResultsOfOperationsIncomeTaxExpense / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_ResultsOfOperationsIncomeTaxExpense / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Results of operations from producing activities | $ (5,859,000)us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | $ 0 us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | $ 0 us-gaap_ResultsOfOperationsOilAndGasProducingActivitiesNetIncomeExcludingCorporateOverheadAndInterestCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember

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- Definition Depreciation, depletion and amortization, and valuation provisions (impairments) related to oil and gas producing activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 + Details
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