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Income Taxes (Narrative) (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Income Tax Reconciliation, Permanent Difference $ 304,000tgc_IncomeTaxReconciliationPermanentDifference $ (4,000)tgc_IncomeTaxReconciliationPermanentDifference $ 49,000tgc_IncomeTaxReconciliationPermanentDifference
Valuation allowance 790,000us-gaap_DeferredTaxAssetsValuationAllowance 790,000us-gaap_DeferredTaxAssetsValuationAllowance  
Federal net operating loss carryforwards 20,200,000us-gaap_OperatingLossCarryforwards    
Operating Loss Carryforwards 20,200,000us-gaap_OperatingLossCarryforwards    
Estimated Net Operating Losses Exceed Gross Financial Reporting Amount [Member]      
Federal net operating loss carryforwards 1,900,000us-gaap_OperatingLossCarryforwards
/ dei_LegalEntityAxis
= tgc_EstimatedNetOperatingLossesExceedGrossFinancialReportingAmountMember
   
Operating Loss Carryforwards $ 1,900,000us-gaap_OperatingLossCarryforwards
/ dei_LegalEntityAxis
= tgc_EstimatedNetOperatingLossesExceedGrossFinancialReportingAmountMember