Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Details)

v2.4.1.9
Fair Value Measurements (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Asset retirement obligation capitalized $ 1,584,000us-gaap_AssetRetirementObligationLiabilitiesIncurred $ 1,869,000us-gaap_AssetRetirementObligationLiabilitiesIncurred  
Mammoth Energy Partners LP [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Equity investment     143,500,000us-gaap_EquityMethodInvestmentsFairValueDisclosure
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_MammothEnergyPartnersLPMember
Level 1 [Member] | Fixed Price Swaps [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fixed price swaps 134,986,000us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= gpor_FixedPriceSwapsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
   
Fixed price swaps 823,000us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= gpor_FixedPriceSwapsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
   
Level 2 [Member] | Fixed Price Swaps [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fixed price swaps 0us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= gpor_FixedPriceSwapsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
   
Fixed price swaps 0us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= gpor_FixedPriceSwapsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
   
Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Asset retirement obligation capitalized 1,600,000us-gaap_AssetRetirementObligationLiabilitiesIncurred
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
   
Level 3 [Member] | Mammoth Energy Partners LP [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Equity investment     143,500,000us-gaap_EquityMethodInvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_MammothEnergyPartnersLPMember
Level 3 [Member] | Fixed Price Swaps [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fixed price swaps 0us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= gpor_FixedPriceSwapsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
   
Fixed price swaps $ 0us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= gpor_FixedPriceSwapsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member