Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Narrative (Details)

v2.4.1.9
Summary of Significant Accounting Policies - Narrative (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Summary Of Significant Accounting Policies [Line Items]        
Accounts receivable, collection period 30 days      
Conversion ratio, gas to barrels of oil 6gpor_ConversionRatioGasToBarrelsOfOil      
Capitalized costs of oil and natural gas properties excluded from amortization $ 1,465,538,000us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative $ 1,020,835,000us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative    
Cumulative translation adjustment (26,675,000)us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax (9,781,000)us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax 2,442,000us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax 1,087,000us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax
Minimum [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Useful life 3 years      
Maximum [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Vesting period 5 years      
Useful life 30 years      
Tatex Thailand III LLC [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Equity Method Investment, Other than Temporary Impairment $ 12,100,000us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_TatexThailandIiiLlcMember 		$ 0us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= gpor_TatexThailandIiiLlcMember 		   
Restricted Stock [Member] | Minimum [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Vesting period 1 year      
Restricted Stock [Member] | Maximum [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Vesting period 5 years      
Customer Concentration Risk [Member] | Accounts Receivable [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Concentration Risk, Number of Purchasers 3gpor_ConcentrationRiskNumberofPurchasers
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember