Annual report pursuant to Section 13 and 15(d)

Supplemental Information On Oil And Gas Exploration And Production Activities (Changes in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves) (Details)

v2.4.1.9
Supplemental Information On Oil And Gas Exploration And Production Activities (Changes in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Changes In Standardized Measure of Discontinued Future Net Cash Flows [Line Items]      
Sales and transfers of oil and gas produced, net of production costs $ (530,098)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts $ (197,559)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts $ (194,893)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts
Net changes in prices, production costs, and development costs 97,716gpor_NetChangesInPricesProductionCostsAndDevelopment 65,573gpor_NetChangesInPricesProductionCostsAndDevelopment 108,941gpor_NetChangesInPricesProductionCostsAndDevelopment
Acquisition of oil and gas reserves in place 14,266us-gaap_IncreaseDueToPurchasesOfMineralsInPlace 0us-gaap_IncreaseDueToPurchasesOfMineralsInPlace 0us-gaap_IncreaseDueToPurchasesOfMineralsInPlace
Extensions and discoveries 790,533us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts 130,826us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts 151,654us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts
Previously estimated development costs incurred during the period 68,227us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod 43,478us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod 10,211us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod
Revisions of previous quantity estimates, less related production costs (37,801)us-gaap_RevisionsOfPreviousQuantityEstimates (3,591)us-gaap_RevisionsOfPreviousQuantityEstimates (10,504)us-gaap_RevisionsOfPreviousQuantityEstimates
Sales of reserves in place 0us-gaap_DecreaseDueToSalesOfMineralsInPlace 0us-gaap_DecreaseDueToSalesOfMineralsInPlace (214,867)us-gaap_DecreaseDueToSalesOfMineralsInPlace
Accretion of discount 57,847us-gaap_AccretionOfDiscount 34,864us-gaap_AccretionOfDiscount 37,668us-gaap_AccretionOfDiscount
Net changes in income taxes (295,226)us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves (30,239)us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves 25,585us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves
Change in production rates and other 683,237gpor_ChangeInProductionRatesAndOther 186,473gpor_ChangeInProductionRatesAndOther 58,165gpor_ChangeInProductionRatesAndOther
Total change in standardized measure of discounted future net cash flows 848,701us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease 229,825us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease (28,040)us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease
Diamondback Energy, Inc [Member]      
Changes In Standardized Measure of Discontinued Future Net Cash Flows [Line Items]      
Sales and transfers of oil and gas produced, net of production costs 0us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
(12,524)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
(11,601)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Net changes in prices, production costs, and development costs 0gpor_NetChangesInPricesProductionCostsAndDevelopment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
3,312gpor_NetChangesInPricesProductionCostsAndDevelopment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
(14,596)gpor_NetChangesInPricesProductionCostsAndDevelopment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Acquisition of oil and gas reserves in place 0us-gaap_IncreaseDueToPurchasesOfMineralsInPlace
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
21,968us-gaap_IncreaseDueToPurchasesOfMineralsInPlace
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
23,090us-gaap_IncreaseDueToPurchasesOfMineralsInPlace
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Extensions and discoveries 0us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
39,776us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
16,969us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Previously estimated development costs incurred during the period 0us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
5,517us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
19,014us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Revisions of previous quantity estimates, less related production costs 0us-gaap_RevisionsOfPreviousQuantityEstimates
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
(9,143)us-gaap_RevisionsOfPreviousQuantityEstimates
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
(4,897)us-gaap_RevisionsOfPreviousQuantityEstimates
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Accretion of discount 0us-gaap_AccretionOfDiscount
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
4,175us-gaap_AccretionOfDiscount
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
7,803us-gaap_AccretionOfDiscount
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Net changes in income taxes 0us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
(12,137)us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
(26,866)us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Change in production rates and other 0gpor_ChangeInProductionRatesAndOther
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
2,862gpor_ChangeInProductionRatesAndOther
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
(8,358)gpor_ChangeInProductionRatesAndOther
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Total change in standardized measure of discounted future net cash flows 0us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
(8,339)us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
558us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Equity Method Investment, Change in Ownership 0gpor_EquityMethodInvestmentChangeinOwnership
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
(52,145)gpor_EquityMethodInvestmentChangeinOwnership
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
0gpor_EquityMethodInvestmentChangeinOwnership
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Grizzly Oil Sands ULC [Member]      
Changes In Standardized Measure of Discontinued Future Net Cash Flows [Line Items]      
Sales and transfers of oil and gas produced, net of production costs (4,664)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Net changes in prices, production costs, and development costs 76,518gpor_NetChangesInPricesProductionCostsAndDevelopment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0gpor_NetChangesInPricesProductionCostsAndDevelopment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0gpor_NetChangesInPricesProductionCostsAndDevelopment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Acquisition of oil and gas reserves in place 0us-gaap_IncreaseDueToPurchasesOfMineralsInPlace
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_IncreaseDueToPurchasesOfMineralsInPlace
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_IncreaseDueToPurchasesOfMineralsInPlace
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Extensions and discoveries 7,107us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Previously estimated development costs incurred during the period 0us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Revisions of previous quantity estimates, less related production costs (10,659)us-gaap_RevisionsOfPreviousQuantityEstimates
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_RevisionsOfPreviousQuantityEstimates
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_RevisionsOfPreviousQuantityEstimates
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Accretion of discount 14,946us-gaap_AccretionOfDiscount
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_AccretionOfDiscount
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_AccretionOfDiscount
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Net changes in income taxes 9,162us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Change in production rates and other (25,738)gpor_ChangeInProductionRatesAndOther
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0gpor_ChangeInProductionRatesAndOther
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0gpor_ChangeInProductionRatesAndOther
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Total change in standardized measure of discounted future net cash flows $ (55,718)us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
$ 0us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
$ 0us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember