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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
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Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items] |  |
Total oil and gas properties not subject to amortization, total | $ 1,546,804 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative | $ 1,465,538 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative
Colorado [Member] |  |
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items] |  |
Total oil and gas properties not subject to amortization, total | 5,088 us-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 | 96 us-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 | 283 us-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 | 1,541,292 us-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 | $ 45 us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationCumulative / us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis = gpor_OtherPropertiesMember |

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- Definition The sum of the capitalized costs incurred, as of the balance sheet date, of unproved properties excluded from amortization including acquisition costs, exploration costs, development costs, and production costs. + 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=50486907&loc=d3e511914-122862 + Details
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