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Acquisitions - Fair Value of Assets Acquired (Details) (Utica Shale [Member], USD $) In Thousands, unless otherwise specified | 0 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 20, 2014 | Dec. 31, 2014 | Mar. 20, 2014
Business Acquisition [Line Items] |  |  |
Cash, net of purchase price adjustments | $ 179,527 gpor_PaymenttoAcquireOilandGasPropertyandEquipmentNet | $ 179,500 gpor_PaymenttoAcquireOilandGasPropertyandEquipmentNet |
Fair value of net identifiable assets acquired | 179,527 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment |  | 179,527 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
Proved Properties [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Fair value of net identifiable assets acquired | 31,961 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = gpor_ProvedPropertiesMember |  | 31,961 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = gpor_ProvedPropertiesMember
Unproved Properties [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Fair value of net identifiable assets acquired | 6,263 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = gpor_UnprovedPropertiesMember |  | 6,263 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = gpor_UnprovedPropertiesMember
Unevaluated Properties [Member] |  |  |
Business Acquisition [Line Items] |  |  |
Fair value of net identifiable assets acquired | $ 141,303 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = gpor_UnevaluatedPropertiesMember |  | $ 141,303 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = gpor_UticaShaleMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = gpor_UnevaluatedPropertiesMember

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- Definition Payment to Acquire Oil and Gas Property and Equipment, Net + References No definition available. + Details
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- Details
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- Definition The amount of property, plant, and equipment recognized as of the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=25498275&loc=d3e2207-128464 + Details
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