Annual report pursuant to Section 13 and 15(d)

Supplemental Information On Oil And Gas Exploration And Production Activities (Narrative) (Details)

v2.4.1.9
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