Annual report pursuant to Section 13 and 15(d)

Property And Equipment (Narrative) (Details)

v2.4.1.9
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 $ 72,700,000gpor_CumulativeCapitalizationOfGeneralAndAdministrativeCostsIncurredAndCapitalizedToFullCostPool $ 47,500,000gpor_CumulativeCapitalizationOfGeneralAndAdministrativeCostsIncurredAndCapitalizedToFullCostPool          
Capitalized general and administrative costs 25,200,000gpor_CapitalizedGeneralAndAdministrativeCosts 14,900,000gpor_CapitalizedGeneralAndAdministrativeCosts 9,100,000gpor_CapitalizedGeneralAndAdministrativeCosts        
Capitalized costs of oil and natural gas properties excluded from amortization 1,465,538,000us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative 1,020,835,000us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative          
Loss on disposal of Belize properties, net of tax 0us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax 0us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax (3,465,000)us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax        
Payment received from Diamondback 45,034,000us-gaap_IncreaseDecreaseInAccountsReceivable 33,209,000us-gaap_IncreaseDecreaseInAccountsReceivable (2,404,000)us-gaap_IncreaseDecreaseInAccountsReceivable        
Gain on sale of oil and gas property 11,000us-gaap_GainLossOnSaleOfOilAndGasProperty (508,000)us-gaap_GainLossOnSaleOfOilAndGasProperty 7,300,000us-gaap_GainLossOnSaleOfOilAndGasProperty        
Oil and gas property, decrease related to contribution   213,000,000gpor_OilAndGasPropertyFullCostMethodGrossPeriodDecrease          
Diamondback [Member]              
Property, Plant and Equipment [Line Items]              
Investment (shares)           7,914,036us-gaap_InvestmentOwnedBalanceShares
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= gpor_DiamondbackMember 		 
Promissory note receivable           63,600,000us-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 1gpor_NumberOfDirectorsAllowedToServeOnBoardOfDirectors
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= gpor_DiamondbackMember 		           
Number of advisors allowed to serve on Board 1gpor_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       $ 18,600,000us-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