Subsequent Events (Details) (USD $)
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3 Months Ended |
0 Months Ended |
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Mar. 31, 2014
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Sep. 30, 2015
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Apr. 21, 2015
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Apr. 29, 2015
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Apr. 16, 2015
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Mar. 31, 2015
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Aug. 18, 2014
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Dec. 21, 2012
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Oct. 17, 2012
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Apr. 30, 2015
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Apr. 15, 2015
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Subsequent Event [Line Items] |
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Proceeds from issuance of common stock, net of offering costs and exercise of stock options |
$ 615,000us-gaap_ProceedsFromIssuanceOfCommonStock
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Fixed Price Swap, October through December 2015 [Member] |
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Subsequent Event [Line Items] |
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Daily Volume (in MMBtu per day) |
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262,500invest_DerivativeNonmonetaryNotionalAmount / us-gaap_DerivativeByNatureAxis = gpor_FixedPriceSwapOctoberthroughDecember2015Member
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Weighted Average Price (in usd per MMBtu) |
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3.96us-gaap_DerivativeSwapTypeAverageFixedPrice / us-gaap_DerivativeByNatureAxis = gpor_FixedPriceSwapOctoberthroughDecember2015Member
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Senior Notes [Member] |
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Subsequent Event [Line Items] |
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Stated interest rate |
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7.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember
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7.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember
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7.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember
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Scenario, Forecast [Member] | Paloma Partners III, LLC [Member] |
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Subsequent Event [Line Items] |
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Purchase price |
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301,300,000us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = gpor_PalomaPartnersIIILLCMember / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember
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Subsequent Event [Member] |
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Subsequent Event [Line Items] |
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Proceeds from issuance of common stock, net of offering costs and exercise of stock options |
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501,900,000us-gaap_ProceedsFromIssuanceOfCommonStock / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Subsequent Event [Member] | Fixed Price Swap, June 2015 through June 2016 [Member] |
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Subsequent Event [Line Items] |
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Daily Volume (in MMBtu per day) |
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1,500invest_DerivativeNonmonetaryNotionalAmount / us-gaap_DerivativeByNatureAxis = gpor_FixedPriceSwapJune2015throughJune2016Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Weighted Average Price (in usd per MMBtu) |
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62.47us-gaap_DerivativeSwapTypeAverageFixedPrice / us-gaap_DerivativeByNatureAxis = gpor_FixedPriceSwapJune2015throughJune2016Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Subsequent Event [Member] | Fixed Price Swap, October through December 2015 [Member] |
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Subsequent Event [Line Items] |
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Daily Volume (in MMBtu per day) |
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20,000invest_DerivativeNonmonetaryNotionalAmount / us-gaap_DerivativeByNatureAxis = gpor_FixedPriceSwapOctoberthroughDecember2015Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Weighted Average Price (in usd per MMBtu) |
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3.26us-gaap_DerivativeSwapTypeAverageFixedPrice / us-gaap_DerivativeByNatureAxis = gpor_FixedPriceSwapOctoberthroughDecember2015Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Subsequent Event [Member] | Fixed Price Swap, January 2016 through December 2016 [Member] |
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Subsequent Event [Line Items] |
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Daily Volume (in MMBtu per day) |
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40,000invest_DerivativeNonmonetaryNotionalAmount / us-gaap_DerivativeByNatureAxis = gpor_FixedPriceSwapJanuary2016throughDecember2016Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Weighted Average Price (in usd per MMBtu) |
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3.32us-gaap_DerivativeSwapTypeAverageFixedPrice / us-gaap_DerivativeByNatureAxis = gpor_FixedPriceSwapJanuary2016throughDecember2016Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Subsequent Event [Member] | Fixed Price Swap, January 2017 through December 2018 [Member] |
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Subsequent Event [Line Items] |
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Daily Volume (in MMBtu per day) |
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20,000invest_DerivativeNonmonetaryNotionalAmount / us-gaap_DerivativeByNatureAxis = gpor_FixedPriceSwapJanuary2017throughDecember2018Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Weighted Average Price (in usd per MMBtu) |
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3.26us-gaap_DerivativeSwapTypeAverageFixedPrice / us-gaap_DerivativeByNatureAxis = gpor_FixedPriceSwapJanuary2017throughDecember2018Member / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Subsequent Event [Member] | Swaption Contract, January 2016 through December 2016 [Member] [Member] |
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Subsequent Event [Line Items] |
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Daily Volume (in MMBtu per day) |
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20,000invest_DerivativeNonmonetaryNotionalAmount / us-gaap_DerivativeByNatureAxis = gpor_SwaptionContractJanuary2016throughDecember2016MemberMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Weighted Average Price (in usd per MMBtu) |
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3.38us-gaap_DerivativeSwapTypeAverageFixedPrice / us-gaap_DerivativeByNatureAxis = gpor_SwaptionContractJanuary2016throughDecember2016MemberMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Subsequent Event [Member] | Chief Executive Officer [Member] |
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Subsequent Event [Line Items] |
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Employment agreement, annual salary |
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460,000gpor_EmploymentAgreementAnnualCompensation / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember / us-gaap_TitleOfIndividualAxis = us-gaap_ChiefExecutiveOfficerMember
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Subsequent Event [Member] | Restricted Stock [Member] | Chief Executive Officer [Member] |
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Subsequent Event [Line Items] |
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Employment agreement, annual grant (in shares) |
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40,000gpor_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsEmploymentAgreementAnnualGrantofShares / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember / us-gaap_TitleOfIndividualAxis = us-gaap_ChiefExecutiveOfficerMember
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Employment agreement, percent of salary awarded in shares |
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500.00%gpor_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsEmploymentAgreementMaximumAnnalSalaryGrantedinOptionsPercent / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember / us-gaap_TitleOfIndividualAxis = us-gaap_ChiefExecutiveOfficerMember
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Subsequent Event [Member] | Senior Notes [Member] | Notes Due 2023 [Member] |
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Subsequent Event [Line Items] |
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Debt instrument, amount |
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350,000,000us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = gpor_NotesDue2023Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Stated interest rate |
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6.625%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = gpor_NotesDue2023Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Proceeds from debt, net of issuance costs |
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$ 343,600,000us-gaap_ProceedsFromDebtNetOfIssuanceCosts / us-gaap_DebtInstrumentAxis = gpor_NotesDue2023Member / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Subsequent Event [Member] | Common Stock [Member] |
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Subsequent Event [Line Items] |
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Stock issued in underwritten public offering (in shares) |
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10,925,000us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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Subsequent Event [Member] | Common Stock [Member] | Over-Allotment Option [Member] |
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Subsequent Event [Line Items] |
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Stock issued in underwritten public offering (in shares) |
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1,425,000us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_OverAllotmentOptionMember
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Subsequent Event [Member] | Paloma Partners III, LLC [Member] |
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Subsequent Event [Line Items] |
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Gas and oil acreage, undeveloped, net |
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24,000us-gaap_GasAndOilAreaUndevelopedNet / us-gaap_BusinessAcquisitionAxis = gpor_PalomaPartnersIIILLCMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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