Quarterly report pursuant to Section 13 or 15(d)

Property And Equipment (Summary Of Oil And Gas Properties Not Subject To Amortization) (Details)

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Property And Equipment (Summary Of Oil And Gas Properties Not Subject To Amortization) (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total oil and gas properties not subject to amortization, total $ 1,546,804us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative $ 1,465,538us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative
Colorado [Member]    
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total oil and gas properties not subject to amortization, total 5,088us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative
/ us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis
= gpor_ColoradoPropertiesMember 		 
Bakken [Member]    
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total oil and gas properties not subject to amortization, total 96us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative
/ us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis
= gpor_BakkenPropertiesMember 		 
Southern Louisiana [Member]    
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total oil and gas properties not subject to amortization, total 283us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative
/ us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis
= gpor_SouthernLouisianaPropertiesMember 		 
Ohio [Member]    
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total oil and gas properties not subject to amortization, total 1,541,292us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative
/ us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis
= gpor_OhioPropertiesMember 		 
Other [Member]    
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]    
Total oil and gas properties not subject to amortization, total $ 45us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative
/ us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis
= gpor_OtherPropertiesMember