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           Fair Value of Financial Instruments (Details) (USD $) 
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           Dec. 31, 2014 
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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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| Debt Instrument [Line Items] | ||||
| Unamortized discount | $ 2,800,000us-gaap_DebtInstrumentUnamortizedDiscount | |||
| Fair value of notes | 587,600,000us-gaap_DebtInstrumentFairValue | |||
| Senior Notes [Member] | ||||
| Debt Instrument [Line Items] | ||||
| Carrying value of debt | 
614,700,000us-gaap_DebtLongtermAndShorttermCombinedAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember  | 
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| Unamortized discount | 
3,700,000us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember  | 
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| Unamortized premium | 
18,000,000us-gaap_DebtInstrumentUnamortizedPremium / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember  | 
        
500,000us-gaap_DebtInstrumentUnamortizedPremium / us-gaap_LongtermDebtTypeAxis = us-gaap_SeniorNotesMember  | 
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| December Notes [Member] | ||||
| Debt Instrument [Line Items] | ||||
| Unamortized premium | 
400,000us-gaap_DebtInstrumentUnamortizedPremium / us-gaap_DebtInstrumentAxis = gpor_DecemberNotesMember  | 
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| August Notes [Member] | ||||
| Debt Instrument [Line Items] | ||||
| Unamortized premium | 
17,100,000us-gaap_DebtInstrumentUnamortizedPremium / us-gaap_DebtInstrumentAxis = gpor_AugustNotesMember  | 
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| Mammoth Energy Partners LP [Member] | ||||
| Debt Instrument [Line Items] | ||||
| Equity Method Investments, Fair Value Disclosure | 
$ 143,500,000us-gaap_EquityMethodInvestmentsFairValueDisclosure / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = gpor_MammothEnergyPartnersLPMember  | 
        
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- Definition 
          Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          The amount of debt premium that was originally recognized at the issuance of the instrument that has yet to be amortized. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Represents the aggregate of total long-term debt, including current maturities and short-term debt. No definition available. 
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- Definition 
          Fair value portion of investments accounted under the equity method. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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