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

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Total costs incurred in oil and gas properties acquisition and development activities

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Cost incurred, including capitalized costs and costs charged to expense, in acquisition of oil and gas properties.

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Amount of asset retirement obligations (ARO) costs incurred (whether capitalized or charged to expense) during the period.

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Development costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

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Exploration costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

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