Annual report pursuant to Section 13 and 15(d)

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)

v2.4.1.9
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
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 $ 4,667,678us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows $ 1,657,708us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows $ 954,833us-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 2,302,970us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows 859,442us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows 444,654us-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 1,427,167us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure 578,466us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure 348,641us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure
Diamondback Energy, Inc [Member]      
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]      
Future cash flows 0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
331,505us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
592,669us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
Future development and abandonment costs 0us-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 0us-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 0gpor_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 0us-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 0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
164,708us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
209,456us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
10% discount to reflect timing of cash flows 0us-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 0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
70,246us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_DiamondbackEnergyIncMember
78,585us-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 754,720us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Future development and abandonment costs (205,242)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Future production costs (291,988)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Future production taxes 0gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0gpor_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionTaxes
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Future income taxes (11,250)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureIncomeTaxExpense1
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Future net cash flows 246,240us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-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
0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
Standardized measure of discounted future net cash flows $ 93,746us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
$ 0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember
$ 0us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesStandardizedMeasure
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_GrizzlyOilSandsUlcMember