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Manufactured Methane (Manufactured Methane Facilities) (Details) (Methane Project [Member], USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Methane Project [Member]
   
Property, Plant and Equipment [Line Items]    
Manufactured Methane facilities, at cost $ 1,634us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= tgc_MethaneProjectMember
$ 1,634us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= tgc_MethaneProjectMember
Accumulated depreciation (15)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= tgc_MethaneProjectMember
 
Manufactured Methane facilities, net $ 1,619us-gaap_PropertyPlantAndEquipmentNet
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= tgc_MethaneProjectMember
$ 1,634us-gaap_PropertyPlantAndEquipmentNet
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= tgc_MethaneProjectMember