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Property And Equipment (Narrative) (Details) (USD $) | 12 Months Ended | 1 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Jan. 31, 2013 | Oct. 31, 2012 | Oct. 11, 2012 | May 07, 2012
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |
Cumulative capitalization of general and administrative costs incurred and capitalized to the full cost pool | $ 72,700,000 gpor_CumulativeCapitalizationOfGeneralAndAdministrativeCostsIncurredAndCapitalizedToFullCostPool | $ 47,500,000 gpor_CumulativeCapitalizationOfGeneralAndAdministrativeCostsIncurredAndCapitalizedToFullCostPool |  |  |  |  |
Capitalized general and administrative costs | 25,200,000 gpor_CapitalizedGeneralAndAdministrativeCosts | 14,900,000 gpor_CapitalizedGeneralAndAdministrativeCosts | 9,100,000 gpor_CapitalizedGeneralAndAdministrativeCosts |  |  |  |
Capitalized costs of oil and natural gas properties excluded from amortization | 1,465,538,000 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative | 1,020,835,000 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative |  |  |  |  |
Loss on disposal of Belize properties, net of tax | 0 us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax | 0 us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax | (3,465,000)us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax |  |  |  |
Payment received from Diamondback | 45,034,000 us-gaap_IncreaseDecreaseInAccountsReceivable | 33,209,000 us-gaap_IncreaseDecreaseInAccountsReceivable | (2,404,000)us-gaap_IncreaseDecreaseInAccountsReceivable |  |  |  |
Gain on sale of oil and gas property | 11,000 us-gaap_GainLossOnSaleOfOilAndGasProperty | (508,000)us-gaap_GainLossOnSaleOfOilAndGasProperty | 7,300,000 us-gaap_GainLossOnSaleOfOilAndGasProperty |  |  |  |
Oil and gas property, decrease related to contribution |  | 213,000,000 gpor_OilAndGasPropertyFullCostMethodGrossPeriodDecrease |  |  |  |  |
Diamondback [Member] |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |
Investment (shares) |  |  |  |  |  | 7,914,036 us-gaap_InvestmentOwnedBalanceShares / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |
Promissory note receivable |  |  |  |  |  | 63,600,000 us-gaap_NotesAndLoansReceivableNetCurrent / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |
Ownership requirement to meet agreement | 10.00%gpor_OwnershipRequirementToMeetAgreement / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |  |  |  |  |  |
Number of directors allowed to serve on Board | 1 gpor_NumberOfDirectorsAllowedToServeOnBoardOfDirectors / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |  |  |  |  |  |
Number of advisors allowed to serve on Board | 1 gpor_NumberOfAdvisorsAllowedOnBoardOfDirectors / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |  |  |  |  |  |
Ownership interest |  |  |  |  | 21.40%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |  | 35.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember
Diamondback [Member] | Accounts Receivable - Related Party [Member] |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |
Payment received from Diamondback |  |  |  | $ 18,600,000 us-gaap_IncreaseDecreaseInAccountsReceivable / us-gaap_BalanceSheetLocationAxis = gpor_AccountsReceivableRelatedPartyMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = gpor_DiamondbackMember |  |  |
Minimum [Member] |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |
Expected number of years amortization will commence | 3 years |  |  |  |  |  |
Maximum [Member] |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |
Expected number of years amortization will commence | 5 years |  |  |  |  |  |

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