Quarterly report pursuant to Section 13 or 15(d)

Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheets (Details)

v2.4.1.9
Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheets (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Dec. 31, 2013
Current assets:        
Cash and cash equivalents $ 74,740us-gaap_CashAndCashEquivalentsAtCarryingValue $ 142,340us-gaap_CashAndCashEquivalentsAtCarryingValue $ 170,382us-gaap_CashAndCashEquivalentsAtCarryingValue $ 458,956us-gaap_CashAndCashEquivalentsAtCarryingValue
Accounts receivable—oil and gas 79,680us-gaap_AccountsReceivableNetCurrent 103,858us-gaap_AccountsReceivableNetCurrent    
Accounts receivable - related parties 33us-gaap_DueFromRelatedPartiesCurrent 46us-gaap_DueFromRelatedPartiesCurrent    
Accounts receivable - intercompany   0us-gaap_DueFromAffiliateCurrent    
Prepaid expenses and other current assets 15,777us-gaap_PrepaidExpenseAndOtherAssetsCurrent 3,714us-gaap_PrepaidExpenseAndOtherAssetsCurrent    
Short-term derivative instruments 93,030us-gaap_DerivativeAssetsCurrent 78,391us-gaap_DerivativeAssetsCurrent    
Total current assets 263,260us-gaap_AssetsCurrent 328,349us-gaap_AssetsCurrent    
Property and equipment:        
Oil and natural gas properties 4,177,962us-gaap_OilAndGasPropertyFullCostMethodGross 3,923,154us-gaap_OilAndGasPropertyFullCostMethodGross    
Other property and equipment 19,051us-gaap_PropertyPlantAndEquipmentOther 18,344us-gaap_PropertyPlantAndEquipmentOther    
Accumulated depletion, depreciation, amortization and impairment (1,140,168)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment (1,050,879)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment    
Property and equipment, net 3,056,845us-gaap_PropertyPlantAndEquipmentNet 2,890,619us-gaap_PropertyPlantAndEquipmentNet    
Other assets:        
Equity investments and investments in subsidiaries 374,971us-gaap_EquityMethodInvestments 369,581us-gaap_EquityMethodInvestments    
Derivative instruments 41,956us-gaap_DerivativeInstrumentsAndHedgesNoncurrent 24,448us-gaap_DerivativeInstrumentsAndHedgesNoncurrent    
Other assets 18,566us-gaap_OtherAssetsNoncurrent 19,396us-gaap_OtherAssetsNoncurrent    
Total other assets 435,493gpor_TotalOtherAssets 413,425gpor_TotalOtherAssets    
Total assets 3,755,598us-gaap_Assets 3,632,393us-gaap_Assets    
Current liabilities:        
Accounts payable and accrued liabilities 400,096us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent 371,410us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent    
Accounts payable - intercompany 0us-gaap_DueToAffiliateCurrent 0us-gaap_DueToAffiliateCurrent    
Asset retirement obligation—current 75us-gaap_AssetRetirementObligationCurrent 75us-gaap_AssetRetirementObligationCurrent 795us-gaap_AssetRetirementObligationCurrent  
Short-term derivative instruments 823us-gaap_DerivativeLiabilitiesCurrent      
Deferred tax liability - current 29,622us-gaap_DeferredTaxLiabilitiesCurrent 27,070us-gaap_DeferredTaxLiabilitiesCurrent    
Current maturities of long-term debt 1,781us-gaap_LongTermDebtCurrent 168us-gaap_LongTermDebtCurrent    
Total current liabilities 432,397us-gaap_LiabilitiesCurrent 398,723us-gaap_LiabilitiesCurrent    
Long-term derivative instrument 0us-gaap_DerivativeLiabilitiesNoncurrent      
Asset retirement obligation—long-term 18,656us-gaap_AssetRetirementObligationsNoncurrent 17,863us-gaap_AssetRetirementObligationsNoncurrent 14,650us-gaap_AssetRetirementObligationsNoncurrent  
Deferred tax liability 215,122us-gaap_DeferredTaxLiabilitiesGrossNoncurrent 203,195us-gaap_DeferredTaxLiabilitiesGrossNoncurrent    
Long-term debt, net of current maturities 779,130us-gaap_LongTermDebtNoncurrent 716,316us-gaap_LongTermDebtNoncurrent    
Total liabilities 1,445,305us-gaap_Liabilities 1,336,097us-gaap_Liabilities    
Stockholders’ equity:        
Common stock 857us-gaap_CommonStockValue 856us-gaap_CommonStockValue    
Paid-in capital 1,832,063us-gaap_AdditionalPaidInCapital 1,828,602us-gaap_AdditionalPaidInCapital    
Accumulated other comprehensive income (loss) (41,659)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax (26,675)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax    
Retained earnings (accumulated deficit) 519,032us-gaap_RetainedEarningsAccumulatedDeficit 493,513us-gaap_RetainedEarningsAccumulatedDeficit    
Total stockholders’ equity 2,310,293us-gaap_StockholdersEquity 2,296,296us-gaap_StockholdersEquity 2,130,440us-gaap_StockholdersEquity 2,050,238us-gaap_StockholdersEquity
Total liabilities and stockholders’ equity 3,755,598us-gaap_LiabilitiesAndStockholdersEquity 3,632,393us-gaap_LiabilitiesAndStockholdersEquity    
Parent [Member]        
Current assets:        
Cash and cash equivalents 73,667us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
141,535us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
168,476us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
451,431us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Accounts receivable—oil and gas 79,621us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
103,762us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Accounts receivable - related parties 33us-gaap_DueFromRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
46us-gaap_DueFromRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Accounts receivable - intercompany 48,154us-gaap_DueFromAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
45,222us-gaap_DueFromAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Prepaid expenses and other current assets 15,777us-gaap_PrepaidExpenseAndOtherAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
3,714us-gaap_PrepaidExpenseAndOtherAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Short-term derivative instruments 93,030us-gaap_DerivativeAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
78,391us-gaap_DerivativeAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Total current assets 310,282us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
372,670us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Property and equipment:        
Oil and natural gas properties 4,139,903us-gaap_OilAndGasPropertyFullCostMethodGross
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
3,887,874us-gaap_OilAndGasPropertyFullCostMethodGross
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Other property and equipment 19,008us-gaap_PropertyPlantAndEquipmentOther
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
18,301us-gaap_PropertyPlantAndEquipmentOther
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Accumulated depletion, depreciation, amortization and impairment (1,140,142)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
(1,050,855)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Property and equipment, net 3,018,769us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
2,855,320us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Other assets:        
Equity investments and investments in subsidiaries 365,840us-gaap_EquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
360,238us-gaap_EquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Derivative instruments 41,956us-gaap_DerivativeInstrumentsAndHedgesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
24,448us-gaap_DerivativeInstrumentsAndHedgesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Other assets 18,566us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
19,396us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Total other assets 426,362gpor_TotalOtherAssets
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
404,082gpor_TotalOtherAssets
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Total assets 3,755,413us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
3,632,072us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Current liabilities:        
Accounts payable and accrued liabilities 399,912us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
371,089us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Accounts payable - intercompany 0us-gaap_DueToAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_DueToAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Asset retirement obligation—current 75us-gaap_AssetRetirementObligationCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
75us-gaap_AssetRetirementObligationCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Short-term derivative instruments 823us-gaap_DerivativeLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Deferred tax liability - current 29,622us-gaap_DeferredTaxLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
27,070us-gaap_DeferredTaxLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Current maturities of long-term debt 1,781us-gaap_LongTermDebtCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
168us-gaap_LongTermDebtCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Total current liabilities 432,213us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
398,402us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Long-term derivative instrument 0us-gaap_DerivativeLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Asset retirement obligation—long-term 18,656us-gaap_AssetRetirementObligationsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
17,863us-gaap_AssetRetirementObligationsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Deferred tax liability 215,122us-gaap_DeferredTaxLiabilitiesGrossNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
203,195us-gaap_DeferredTaxLiabilitiesGrossNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Long-term debt, net of current maturities 779,130us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
716,316us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Total liabilities 1,445,121us-gaap_Liabilities
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
1,335,776us-gaap_Liabilities
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Stockholders’ equity:        
Common stock 857us-gaap_CommonStockValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
856us-gaap_CommonStockValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Paid-in capital 1,832,062us-gaap_AdditionalPaidInCapital
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
1,828,602us-gaap_AdditionalPaidInCapital
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Accumulated other comprehensive income (loss) (41,659)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
(26,675)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Retained earnings (accumulated deficit) 519,032us-gaap_RetainedEarningsAccumulatedDeficit
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
493,513us-gaap_RetainedEarningsAccumulatedDeficit
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Total stockholders’ equity 2,310,292us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
2,296,296us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Total liabilities and stockholders’ equity 3,755,413us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
3,632,072us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
   
Guarantors [Member]        
Current assets:        
Cash and cash equivalents 1,072us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
804us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
1,906us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
7,525us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
Accounts receivable—oil and gas 59us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
96us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Accounts receivable - related parties 0us-gaap_DueFromRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
0us-gaap_DueFromRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Accounts receivable - intercompany 26us-gaap_DueFromAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
27us-gaap_DueFromAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Prepaid expenses and other current assets   0us-gaap_PrepaidExpenseAndOtherAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Short-term derivative instruments 0us-gaap_DerivativeAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
0us-gaap_DerivativeAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Total current assets 1,157us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
927us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Property and equipment:        
Oil and natural gas properties 38,769us-gaap_OilAndGasPropertyFullCostMethodGross
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
35,990us-gaap_OilAndGasPropertyFullCostMethodGross
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Other property and equipment 43us-gaap_PropertyPlantAndEquipmentOther
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
43us-gaap_PropertyPlantAndEquipmentOther
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Accumulated depletion, depreciation, amortization and impairment (26)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
(24)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Property and equipment, net 38,786us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
36,009us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Other assets:        
Equity investments and investments in subsidiaries   0us-gaap_EquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Derivative instruments 0us-gaap_DerivativeInstrumentsAndHedgesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
0us-gaap_DerivativeInstrumentsAndHedgesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Other assets   0us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Total assets 39,943us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
36,936us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Current liabilities:        
Accounts payable and accrued liabilities 184us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
321us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Accounts payable - intercompany 48,072us-gaap_DueToAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
45,143us-gaap_DueToAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Asset retirement obligation—current   0us-gaap_AssetRetirementObligationCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Deferred tax liability - current   0us-gaap_DeferredTaxLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Current maturities of long-term debt   0us-gaap_LongTermDebtCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Total current liabilities 48,256us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
45,464us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Long-term derivative instrument 0us-gaap_DerivativeLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Asset retirement obligation—long-term 0us-gaap_AssetRetirementObligationsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
0us-gaap_AssetRetirementObligationsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Deferred tax liability   0us-gaap_DeferredTaxLiabilitiesGrossNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Long-term debt, net of current maturities 0us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
0us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Total liabilities 48,256us-gaap_Liabilities
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
45,464us-gaap_Liabilities
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Stockholders’ equity:        
Common stock   0us-gaap_CommonStockValue
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Paid-in capital 321us-gaap_AdditionalPaidInCapital
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
322us-gaap_AdditionalPaidInCapital
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Accumulated other comprehensive income (loss)   0us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Retained earnings (accumulated deficit) (8,634)us-gaap_RetainedEarningsAccumulatedDeficit
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
(8,850)us-gaap_RetainedEarningsAccumulatedDeficit
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Total stockholders’ equity (8,313)us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
(8,528)us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Total liabilities and stockholders’ equity 39,943us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
36,936us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
   
Non-Guarantor [Member]        
Current assets:        
Cash and cash equivalents 1us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
1us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
Accounts receivable—oil and gas 0us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Accounts receivable - related parties 0us-gaap_DueFromRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_DueFromRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Accounts receivable - intercompany 0us-gaap_DueFromAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_DueFromAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Prepaid expenses and other current assets 0us-gaap_PrepaidExpenseAndOtherAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_PrepaidExpenseAndOtherAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Short-term derivative instruments 0us-gaap_DerivativeAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_DerivativeAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Total current assets 1us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
1us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Property and equipment:        
Oil and natural gas properties   0us-gaap_OilAndGasPropertyFullCostMethodGross
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Other property and equipment   0us-gaap_PropertyPlantAndEquipmentOther
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Accumulated depletion, depreciation, amortization and impairment   0us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Property and equipment, net   0us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Other assets:        
Equity investments and investments in subsidiaries 167,186us-gaap_EquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
180,217us-gaap_EquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Derivative instruments 0us-gaap_DerivativeInstrumentsAndHedgesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_DerivativeInstrumentsAndHedgesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Other assets   0us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Total other assets 167,186gpor_TotalOtherAssets
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
180,217gpor_TotalOtherAssets
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Total assets 167,187us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
180,218us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Current liabilities:        
Accounts payable and accrued liabilities   0us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Accounts payable - intercompany 108us-gaap_DueToAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
106us-gaap_DueToAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Asset retirement obligation—current   0us-gaap_AssetRetirementObligationCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Deferred tax liability - current   0us-gaap_DeferredTaxLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Current maturities of long-term debt   0us-gaap_LongTermDebtCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Total current liabilities 108us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
106us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Long-term derivative instrument 0us-gaap_DerivativeLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Asset retirement obligation—long-term 0us-gaap_AssetRetirementObligationsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_AssetRetirementObligationsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Deferred tax liability   0us-gaap_DeferredTaxLiabilitiesGrossNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Long-term debt, net of current maturities 0us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Total liabilities 108us-gaap_Liabilities
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
106us-gaap_Liabilities
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Stockholders’ equity:        
Common stock   0us-gaap_CommonStockValue
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Paid-in capital 233,174us-gaap_AdditionalPaidInCapital
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
227,079us-gaap_AdditionalPaidInCapital
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Accumulated other comprehensive income (loss) (41,659)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
(26,675)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Retained earnings (accumulated deficit) (24,436)us-gaap_RetainedEarningsAccumulatedDeficit
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
(20,292)us-gaap_RetainedEarningsAccumulatedDeficit
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Total stockholders’ equity 167,079us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
180,112us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Total liabilities and stockholders’ equity 167,187us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
180,218us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
   
Eliminations [Member]        
Current assets:        
Cash and cash equivalents 0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
Accounts receivable—oil and gas   0us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Accounts receivable - related parties 0us-gaap_DueFromRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_DueFromRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Accounts receivable - intercompany (48,180)us-gaap_DueFromAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(45,249)us-gaap_DueFromAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Prepaid expenses and other current assets   0us-gaap_PrepaidExpenseAndOtherAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Short-term derivative instruments 0us-gaap_DerivativeAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_DerivativeAssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Total current assets (48,180)us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(45,249)us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Property and equipment:        
Oil and natural gas properties (710)us-gaap_OilAndGasPropertyFullCostMethodGross
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(710)us-gaap_OilAndGasPropertyFullCostMethodGross
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Other property and equipment   0us-gaap_PropertyPlantAndEquipmentOther
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Accumulated depletion, depreciation, amortization and impairment   0us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Property and equipment, net (710)us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(710)us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Other assets:        
Equity investments and investments in subsidiaries (158,055)us-gaap_EquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(170,874)us-gaap_EquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Derivative instruments 0us-gaap_DerivativeInstrumentsAndHedgesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_DerivativeInstrumentsAndHedgesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Other assets   0us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Total other assets (158,055)gpor_TotalOtherAssets
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(170,874)gpor_TotalOtherAssets
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Total assets (206,945)us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(216,833)us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Current liabilities:        
Accounts payable and accrued liabilities   0us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Accounts payable - intercompany (48,180)us-gaap_DueToAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(45,249)us-gaap_DueToAffiliateCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Asset retirement obligation—current   0us-gaap_AssetRetirementObligationCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Deferred tax liability - current   0us-gaap_DeferredTaxLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Current maturities of long-term debt   0us-gaap_LongTermDebtCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Total current liabilities (48,180)us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(45,249)us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Long-term derivative instrument 0us-gaap_DerivativeLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Asset retirement obligation—long-term 0us-gaap_AssetRetirementObligationsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_AssetRetirementObligationsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Deferred tax liability   0us-gaap_DeferredTaxLiabilitiesGrossNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Long-term debt, net of current maturities 0us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Total liabilities (48,180)us-gaap_Liabilities
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(45,249)us-gaap_Liabilities
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Stockholders’ equity:        
Common stock   0us-gaap_CommonStockValue
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Paid-in capital (233,494)us-gaap_AdditionalPaidInCapital
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(227,401)us-gaap_AdditionalPaidInCapital
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Accumulated other comprehensive income (loss) 41,659us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
26,675us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Retained earnings (accumulated deficit) 33,070us-gaap_RetainedEarningsAccumulatedDeficit
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
29,142us-gaap_RetainedEarningsAccumulatedDeficit
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Total stockholders’ equity (158,765)us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(171,584)us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
   
Total liabilities and stockholders’ equity $ (206,945)us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
$ (216,833)us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember