Quarterly report pursuant to Section 13 or 15(d)

Equity Investments (Narrative) (Details)

v2.4.1.9
Equity Investments (Narrative) (Details) (USD $)
3 Months Ended 1 Months Ended 0 Months Ended 1 Months Ended 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2015
Jan. 28, 2014
Nov. 12, 2014
Sep. 30, 2014
Jun. 30, 2014
Dec. 31, 2013
Dec. 31, 2014
Dec. 31, 2012
Oct. 11, 2012
Schedule of Equity Method Investments [Line Items]                      
Payments for equity method investments $ 6,093,000us-gaap_PaymentsToAcquireEquityMethodInvestments $ 23,687,000us-gaap_PaymentsToAcquireEquityMethodInvestments                  
Equity investments and investments in subsidiaries 374,971,000us-gaap_EquityMethodInvestments   374,971,000us-gaap_EquityMethodInvestments           369,581,000us-gaap_EquityMethodInvestments    
(Income) loss from equity method investments (19,975,000)us-gaap_IncomeLossFromEquityMethodInvestments (128,475,000)us-gaap_IncomeLossFromEquityMethodInvestments                  
Distributions received 817,000us-gaap_EquityMethodInvestmentDividendsOrDistributions 0us-gaap_EquityMethodInvestmentDividendsOrDistributions                  
Apico Llc [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Equity shares owned by affiliate (shares) 85,122gpor_EquitySharesOwnedByAffiliateOfInvestment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_ApicoLlcMember
                   
Total shares owned of subaffiliate (shares) 1,000,000gpor_EquityMethodInvestmentTotalSharesOutstandingOfSubaffiliate
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_ApicoLlcMember
                   
Gas and oil area, reserve (acres) 243,000gpor_GasAndOilAreaReserve
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_ApicoLlcMember
                   
Tatex Thailand III, LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Gas and oil area, reserve (acres) 245,000gpor_GasAndOilAreaReserve
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_TatexThailandIiiLlcMember
                   
Ownership interest 17.90%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_TatexThailandIiiLlcMember
  17.90%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_TatexThailandIiiLlcMember
               
Equity investments and investments in subsidiaries 0us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_TatexThailandIiiLlcMember
  0us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_TatexThailandIiiLlcMember
               
(Income) loss from equity method investments 0us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_TatexThailandIiiLlcMember
49,000us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_TatexThailandIiiLlcMember
                 
Grizzly Oil Sands ULC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Gas and oil area, reserve (acres) 830,000gpor_GasAndOilAreaReserve
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
                   
Cash calls paid 6,100,000gpor_EquityMethodInvestmentAmountOfCashCallsBasedOnProportionateOwnershipInterest
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
                   
Increase (decrease) due to foreign currency translation adjustment 15,000,000gpor_EquityMethodInvestmentsIncreaseDecreaseDueToForeignCurrencyTranslationAdjustment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
7,300,000gpor_EquityMethodInvestmentsIncreaseDecreaseDueToForeignCurrencyTranslationAdjustment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
                 
Ownership interest 24.9999%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
  24.9999%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
               
Equity investments and investments in subsidiaries 167,186,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
  167,186,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
          180,218,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
   
(Income) loss from equity method investments 4,142,000us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
2,001,000us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
                 
Windsor Midstream LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Ownership interest 22.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_WindsorMidstreamLlcMember
  22.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_WindsorMidstreamLlcMember
               
Equity investments and investments in subsidiaries 32,292,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_WindsorMidstreamLlcMember
  32,292,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_WindsorMidstreamLlcMember
          13,505,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_WindsorMidstreamLlcMember
   
(Income) loss from equity method investments (18,787,000)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_WindsorMidstreamLlcMember
(168,000)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_WindsorMidstreamLlcMember
                 
Windsor Midstream LLC [Member] | MidMar Gas LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Ownership interest                   28.40%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ dei_LegalEntityAxis
= gpor_MidmarGasLlcMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_WindsorMidstreamLlcMember
 
Coronado Midstream [Member] | Windsor Midstream LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Proceeds from sale of interest in partnership unit     600,000,000us-gaap_ProceedsFromSaleOfEquityMethodInvestments
/ dei_LegalEntityAxis
= gpor_WindsorMidstreamLlcMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_CoronadoMidstreamMember
               
Gain on sale on investment     85,500,000us-gaap_GainLossOnSaleOfEquityInvestments
/ dei_LegalEntityAxis
= gpor_WindsorMidstreamLlcMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_CoronadoMidstreamMember
               
Blackhawk Midstream LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Ownership interest 48.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_BlackhawkMidstreamLlcMember
  48.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_BlackhawkMidstreamLlcMember
               
Equity investments and investments in subsidiaries 0us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_BlackhawkMidstreamLlcMember
  0us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_BlackhawkMidstreamLlcMember
          0us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_BlackhawkMidstreamLlcMember
   
(Income) loss from equity method investments (7,217,000)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_BlackhawkMidstreamLlcMember
(84,787,000)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_BlackhawkMidstreamLlcMember
                 
Blackhawk Midstream LLC [Member] | Ohio Gathering Company, LLC and Ohio Condensate Company, LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Purchase price of sold equity interests       190,000,000us-gaap_ProceedsFromDivestitureOfBusinesses
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= gpor_OhioGatheringCompanyLLCandOhioCondensateCompanyLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_BlackhawkMidstreamLlcMember
             
Amount put in escrow       14,300,000us-gaap_EscrowDeposit
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= gpor_OhioGatheringCompanyLLCandOhioCondensateCompanyLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_BlackhawkMidstreamLlcMember
             
Proceeds from release of escrow deposits 7,200,000us-gaap_EscrowDepositDisbursementsRelatedToPropertyAcquisition1
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= gpor_OhioGatheringCompanyLLCandOhioCondensateCompanyLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_BlackhawkMidstreamLlcMember
                   
Distributions received   84,800,000us-gaap_EquityMethodInvestmentDividendsOrDistributions
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= gpor_OhioGatheringCompanyLLCandOhioCondensateCompanyLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_BlackhawkMidstreamLlcMember
                 
Diamondback Energy, Inc [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Ownership interest 0.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
  0.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
               
Investment (shares)                     7,914,036us-gaap_InvestmentOwnedBalanceShares
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Equity investments and investments in subsidiaries 0us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
  0us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
          0us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
  138,500,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Number of shares issued in transaction (shares)         942,000us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
1,437,500us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
1,000,000us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
4,534,536us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
     
Proceeds received from sale of stock         60,800,000us-gaap_SaleOfStockConsiderationReceivedOnTransaction
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
197,600,000us-gaap_SaleOfStockConsiderationReceivedOnTransaction
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
  192,700,000us-gaap_SaleOfStockConsiderationReceivedOnTransaction
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
     
(Income) loss from equity method investments 0us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
(48,767,000)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
                 
Sturgeon Acquisitions LLC [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Payments for equity method investments                 20,700,000us-gaap_PaymentsToAcquireEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_SturgeonAcquisitionsLLCMember
   
Ownership interest 25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_SturgeonAcquisitionsLLCMember
  25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_SturgeonAcquisitionsLLCMember
          25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_SturgeonAcquisitionsLLCMember
   
Equity investments and investments in subsidiaries 22,258,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_SturgeonAcquisitionsLLCMember
  22,258,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_SturgeonAcquisitionsLLCMember
          22,507,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_SturgeonAcquisitionsLLCMember
   
(Income) loss from equity method investments (568,000)us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_SturgeonAcquisitionsLLCMember
0us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_SturgeonAcquisitionsLLCMember
                 
Distributions received 800,000us-gaap_EquityMethodInvestmentDividendsOrDistributions
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_SturgeonAcquisitionsLLCMember
                   
Mammoth Energy Partners LP [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Ownership interest 30.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_MammothEnergyPartnersLPMember
  30.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_MammothEnergyPartnersLPMember
          30.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_MammothEnergyPartnersLPMember
   
Equity investments and investments in subsidiaries 143,807,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_MammothEnergyPartnersLPMember
  143,807,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_MammothEnergyPartnersLPMember
          143,973,000us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_MammothEnergyPartnersLPMember
   
(Income) loss from equity method investments 2,372,000us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_MammothEnergyPartnersLPMember
0us-gaap_IncomeLossFromEquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_MammothEnergyPartnersLPMember
                 
Equity investment in Mammoth Energy Partners                 $ 143,500,000us-gaap_EquityMethodInvestmentsFairValueDisclosure
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_MammothEnergyPartnersLPMember