Annual report pursuant to Section 13 and 15(d)

Acquisitions - Fair Value of Assets Acquired (Details)

v2.4.1.9
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 $ 179,527gpor_PaymenttoAcquireOilandGasPropertyandEquipmentNet $ 179,500gpor_PaymenttoAcquireOilandGasPropertyandEquipmentNet  
Fair value of net identifiable assets acquired 179,527us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment   179,527us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
Proved Properties [Member]      
Business Acquisition [Line Items]      
Fair value of net identifiable assets acquired 31,961us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= gpor_ProvedPropertiesMember
  31,961us-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 6,263us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= gpor_UnprovedPropertiesMember
  6,263us-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 $ 141,303us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= gpor_UnevaluatedPropertiesMember
  $ 141,303us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
/ us-gaap_BusinessAcquisitionAxis
= gpor_UticaShaleMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= gpor_UnevaluatedPropertiesMember