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Supplemental Information On Oil And Gas Exploration And Production Activities (Costs Incurred In Oil and Gas Property Acquisition and Development Activities) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items] |  |  |
Acquisition | $ 440,288 us-gaap_CostsIncurredAcquisitionOfOilAndGasProperties | $ 338,153 us-gaap_CostsIncurredAcquisitionOfOilAndGasProperties | $ 513,904 us-gaap_CostsIncurredAcquisitionOfOilAndGasProperties
Development of proved undeveloped properties | 864,511 us-gaap_CostsIncurredDevelopmentCosts | 408,121 us-gaap_CostsIncurredDevelopmentCosts | 121,787 us-gaap_CostsIncurredDevelopmentCosts
Exploratory | 2,249 us-gaap_CostsIncurredExplorationCosts | 26,174 us-gaap_CostsIncurredExplorationCosts | 93,397 us-gaap_CostsIncurredExplorationCosts
Recompletions | 45,658 gpor_CostsIncurredRecompletionsOfOilAndGasProperties | 44,633 gpor_CostsIncurredRecompletionsOfOilAndGasProperties | 24,643 gpor_CostsIncurredRecompletionsOfOilAndGasProperties
Capitalized asset retirement obligation | 2,095 us-gaap_CostsIncurredAssetRetirementObligationIncurred | 3,556 us-gaap_CostsIncurredAssetRetirementObligationIncurred | 2,195 us-gaap_CostsIncurredAssetRetirementObligationIncurred
Total | 1,354,801 gpor_TotalCostsIncurredInOilAndGasPropertiesAcquisitionAndDevelopmentActivities | 820,637 gpor_TotalCostsIncurredInOilAndGasPropertiesAcquisitionAndDevelopmentActivities | 755,926 gpor_TotalCostsIncurredInOilAndGasPropertiesAcquisitionAndDevelopmentActivities
Diamondback Energy, Inc [Member] |  |  |
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items] |  |  |
Acquisition | 0 us-gaap_CostsIncurredAcquisitionOfOilAndGasProperties / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 44,534 us-gaap_CostsIncurredAcquisitionOfOilAndGasProperties / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 49,895 us-gaap_CostsIncurredAcquisitionOfOilAndGasProperties / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Development of proved undeveloped properties | 0 us-gaap_CostsIncurredDevelopmentCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 6,369 us-gaap_CostsIncurredDevelopmentCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 22,740 us-gaap_CostsIncurredDevelopmentCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Exploratory | 0 us-gaap_CostsIncurredExplorationCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 17,491 us-gaap_CostsIncurredExplorationCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 3,755 us-gaap_CostsIncurredExplorationCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Capitalized asset retirement obligation | 0 us-gaap_CostsIncurredAssetRetirementObligationIncurred / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 50 us-gaap_CostsIncurredAssetRetirementObligationIncurred / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 203 us-gaap_CostsIncurredAssetRetirementObligationIncurred / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Total | 0 gpor_TotalCostsIncurredInOilAndGasPropertiesAcquisitionAndDevelopmentActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 68,444 gpor_TotalCostsIncurredInOilAndGasPropertiesAcquisitionAndDevelopmentActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 76,593 gpor_TotalCostsIncurredInOilAndGasPropertiesAcquisitionAndDevelopmentActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Grizzly Oil Sands ULC [Member] |  |  |
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items] |  |  |
Acquisition | 1,230 us-gaap_CostsIncurredAcquisitionOfOilAndGasProperties / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_CostsIncurredAcquisitionOfOilAndGasProperties / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_CostsIncurredAcquisitionOfOilAndGasProperties / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Development of proved undeveloped properties | 7,107 us-gaap_CostsIncurredDevelopmentCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_CostsIncurredDevelopmentCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_CostsIncurredDevelopmentCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Exploratory | 0 us-gaap_CostsIncurredExplorationCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_CostsIncurredExplorationCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_CostsIncurredExplorationCosts / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Capitalized asset retirement obligation | 1,055 us-gaap_CostsIncurredAssetRetirementObligationIncurred / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_CostsIncurredAssetRetirementObligationIncurred / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_CostsIncurredAssetRetirementObligationIncurred / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Total | $ 9,392 gpor_TotalCostsIncurredInOilAndGasPropertiesAcquisitionAndDevelopmentActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | $ 0 gpor_TotalCostsIncurredInOilAndGasPropertiesAcquisitionAndDevelopmentActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | $ 0 gpor_TotalCostsIncurredInOilAndGasPropertiesAcquisitionAndDevelopmentActivities / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember

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- Definition Total costs incurred in oil and gas properties acquisition and development activities + References No definition available. + Details
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- Definition Cost incurred, including capitalized costs and costs charged to expense, in acquisition of oil and gas properties. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 18 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62014-109447 + Details
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- Definition Amount of asset retirement obligations (ARO) costs incurred (whether capitalized or charged to expense) during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Development costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 18 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62014-109447 + Details
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- Definition Exploration costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Exploration -URI http://asc.fasb.org/extlink&oid=6512329 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 18 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62014-109447 + Details
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