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Supplemental Information On Oil And Gas Exploration And Production Activities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reserve Quantities [Line Items]
Price per unit (usd per MMbls or MMcf)	4.35us-gaap_AverageSalesPrices	3.67us-gaap_AverageSalesPrices	2.76us-gaap_AverageSalesPrices
Future development costs estimated to be spend in 2015	$ 221.0gpor_FutureDevelopmentCostsEstimatedToBeSpentInYearOne
Future development costs estimated to be spend in 2016	93.1gpor_FutureDevelopmentCostsEstimatedToBeSpentInYearTwo
Future development costs estimated to be spend in 2017	$ 215.4gpor_FutureDevelopmentCostsEstimatedToBeSpentInYearThree
Diamondback Energy, Inc [Member]
Reserve Quantities [Line Items]
Ownership interest	0.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember	7.20%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember	21.40%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Increase (decrease) in reserve during the period			75,384,000gpor_ProvedDevelopedAndUndevelopedReserveIncreaseDecreaseInReserves / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Grizzly [Member]
Reserve Quantities [Line Items]
Ownership interest	25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyMember
Utica Shale [Member]
Reserve Quantities [Line Items]
Increase (decrease) in reserve during the period	786,347,000gpor_ProvedDevelopedAndUndevelopedReserveIncreaseDecreaseInReserves / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_UticaShaleMember	166,832,000gpor_ProvedDevelopedAndUndevelopedReserveIncreaseDecreaseInReserves / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_UticaShaleMember	40,049,000gpor_ProvedDevelopedAndUndevelopedReserveIncreaseDecreaseInReserves / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_UticaShaleMember
Southern Louisiana and Utica Fields [Member]
Reserve Quantities [Line Items]
Decrease in reserves relating to change in estimates			15,837,000gpor_ProvedDevelopedAndUndevelopedReserveRevisionsOfPreviousEstimatesEnergy / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_SouthernLouisianaandUticaFieldsMember
Rhino [Member]
Reserve Quantities [Line Items]
Increase (decrease) in reserve during the period	12,019,000gpor_ProvedDevelopedAndUndevelopedReserveIncreaseDecreaseInReserves / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_RhinoMember
Niobrara [Member]
Reserve Quantities [Line Items]
Increase (decrease) in reserve during the period			1,748,000gpor_ProvedDevelopedAndUndevelopedReserveIncreaseDecreaseInReserves / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_NiobraraMember
Oil [Member]
Reserve Quantities [Line Items]
Price per unit (usd per MMbls or MMcf)	94.99us-gaap_AverageSalesPrices / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember
Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Price per unit (usd per MMbls or MMcf)	44.84us-gaap_AverageSalesPrices / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember	41.23us-gaap_AverageSalesPrices / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember

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The revenues derived from sales of oil or gas in each geographic area during the reporting period divided by the number of barrels of oil produced or thousands of cubic feet of gas produced.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Industry Guide

-Number 2

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

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