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Property And Equipment (Summary Of Oil And Gas Properties Not Subject To Amortization) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items] |  |  |  |
Acquisition costs | $ 405,226 us-gaap_AcquisitionCosts | $ 323,515 us-gaap_AcquisitionCosts | $ 459,151 us-gaap_AcquisitionCosts | $ 93,864 us-gaap_AcquisitionCosts
Acquisition costs, total | 1,281,756 us-gaap_AcquisitionCostsCumulative |  |  |
Exploration costs | 0 us-gaap_ExplorationCosts | 0 us-gaap_ExplorationCosts | 0 us-gaap_ExplorationCosts | 0 us-gaap_ExplorationCosts
Exploration costs, total | 0 us-gaap_ExplorationCostsCumulative |  |  |
Development costs | 173,693 us-gaap_DevelopmentCosts | 1,801 us-gaap_DevelopmentCosts | 506 us-gaap_DevelopmentCosts | 0 us-gaap_DevelopmentCosts
Development costs, total | 176,000 us-gaap_DevelopmentCostsCumulative |  |  |
Capitalized interest | 5,204 gpor_InterestCostCapitalizedNotSubjecttoAmortization | 2,578 gpor_InterestCostCapitalizedNotSubjecttoAmortization | 0 gpor_InterestCostCapitalizedNotSubjecttoAmortization | 0 gpor_InterestCostCapitalizedNotSubjecttoAmortization
Capitalized interest, total | 7,782 us-gaap_AccumulatedCapitalizedInterestCosts |  |  |
Total oil and gas properties not subject to amortization | 584,123 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortization | 327,894 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortization | 459,657 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortization | 93,864 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortization
Total oil and gas properties not subject to amortization, total | 1,465,538 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative | 1,020,835 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative |  |
Colorado Properties [Member] |  |  |  |
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items] |  |  |  |
Total oil and gas properties not subject to amortization, total | 5,127 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative / us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis = gpor_ColoradoPropertiesMember |  |  |
Bakken Properties [Member] |  |  |  |
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items] |  |  |  |
Total oil and gas properties not subject to amortization, total | 96 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative / us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis = gpor_BakkenPropertiesMember |  |  |
Southern Louisiana Properties [Member] |  |  |  |
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items] |  |  |  |
Total oil and gas properties not subject to amortization, total | 145 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative / us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis = gpor_SouthernLouisianaPropertiesMember |  |  |
Ohio Properties [Member] |  |  |  |
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items] |  |  |  |
Total oil and gas properties not subject to amortization, total | 1,460,125 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative / us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis = gpor_OhioPropertiesMember |  |  |
Other Properties [Member] |  |  |  |
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items] |  |  |  |
Total oil and gas properties not subject to amortization, total | $ 45 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative / us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis = gpor_OtherPropertiesMember |  |  |

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- Definition The capitalized costs incurred during the period (excluded from amortization) to purchase, lease or otherwise acquire an unproved property, including costs of lease bonuses and options to purchase or lease properties, the portion of costs applicable to minerals when land including mineral rights is purchased in fee, brokers' fees, recording fees, legal costs, and other costs incurred in acquiring properties. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-10.(c)(7)(ii)) -URI http://asc.fasb.org/extlink&oid=27015464&loc=d3e511914-122862 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 10 -Paragraph c -Subparagraph 3(ii)(A) -Article 4 + Details
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- Definition The capitalized costs incurred (excluded from amortization), as of the date of the balance sheet, to purchase, lease or otherwise acquire an unproved property, including costs of lease bonuses and options to purchase or lease properties, the portion of costs applicable to minerals when land including mineral rights is purchased in fee, brokers' fees, recording fees, legal costs, and other costs incurred in acquiring properties. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-10.(c)(7)(ii)) -URI http://asc.fasb.org/extlink&oid=27015464&loc=d3e511914-122862 + Details
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- Definition The capitalized costs incurred during the period (excluded from amortization) to obtain access to proved reserves and to provide facilities for extracting, treating, gathering and storing the oil and gas. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-10.(c)(7)(ii)) -URI http://asc.fasb.org/extlink&oid=27015464&loc=d3e511914-122862 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 10 -Paragraph c -Subparagraph 3(ii)(A) -Article 4 + Details
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