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Supplemental Information On Oil And Gas Exploration And Production Activities (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
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items] |  |  |
Future cash flows | $ 4,667,678 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows | $ 1,657,708 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows | $ 954,833 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows
Future development and abandonment costs | (719,898)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 | (272,500)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 | (159,113)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1
Future production costs | (880,427)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 | (274,428)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 | (147,024)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1
Future production taxes | (71,229)gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes | (78,647)gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes | (89,175)gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes
Future income taxes | (693,154)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1 | (172,691)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1 | (114,867)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1
Future net cash flows | 2,302,970 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows | 859,442 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows | 444,654 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows
10% discount to reflect timing of cash flows | (875,803)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows | (280,976)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows | (96,013)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows
Standardized measure of discounted future net cash flows | 1,427,167 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure | 578,466 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure | 348,641 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure
Diamondback Energy, Inc [Member] |  |  |
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items] |  |  |
Future cash flows | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 331,505 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 592,669 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Future development and abandonment costs | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (37,229)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (115,869)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Future production costs | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (58,096)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (165,553)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Future production taxes | 0 gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (22,925)gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (30,122)gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Future income taxes | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (48,547)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (71,669)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Future net cash flows | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 164,708 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 209,456 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
10% discount to reflect timing of cash flows | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (94,462)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | (130,871)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Standardized measure of discounted future net cash flows | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 70,246 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember | 78,585 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_DiamondbackEnergyIncMember
Grizzly Oil Sands ULC [Member] |  |  |
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items] |  |  |
Future cash flows | 754,720 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Future development and abandonment costs | (205,242)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Future production costs | (291,988)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Future production taxes | 0 gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Future income taxes | (11,250)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1 / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Future net cash flows | 246,240 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
10% discount to reflect timing of cash flows | (152,494)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember
Standardized measure of discounted future net cash flows | $ 93,746 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | $ 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember | $ 0 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_GrizzlyOilSandsUlcMember

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- Definition Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves Future Production Taxes + References No definition available. + Details
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- Definition This is the amount that is derived from using a discount rate of ten percent a year to reflect the timing of the future net cash flows relating to proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of estimated future cash inflows from sale of proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of estimated future cost to be incurred in developing proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of estimated future income tax expense to be incurred based on the future income less future expense derived from production and sale of proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of estimated net future cash inflows, after subtracting future development and production costs and future income tax expenses, from sale of proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of estimated future cost to be incurred in producing proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition This amount is the future net cash flows less the computed discount. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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