Annual report pursuant to Section 13 and 15(d)

Fair Value of Financial Instruments (Details)

v2.4.1.9
Fair Value of Financial Instruments (Details) (USD $)
Dec. 31, 2014
Aug. 18, 2014
Dec. 21, 2012
Oct. 17, 2012
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
     
Unamortized discount       3,700,000us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
Unamortized premium   18,000,000us-gaap_DebtInstrumentUnamortizedPremium
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
500,000us-gaap_DebtInstrumentUnamortizedPremium
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
 
December Notes [Member]        
Debt Instrument [Line Items]        
Unamortized premium 400,000us-gaap_DebtInstrumentUnamortizedPremium
/ us-gaap_DebtInstrumentAxis
= gpor_DecemberNotesMember
     
August Notes [Member]        
Debt Instrument [Line Items]        
Unamortized premium 17,100,000us-gaap_DebtInstrumentUnamortizedPremium
/ us-gaap_DebtInstrumentAxis
= gpor_AugustNotesMember
     
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