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Supplemental Oil And Gas Information (Schedule Of Changes In The Standardized Measure Of Discounted Future Net Cash Flows From Proved Oil And Gas Reserves) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Supplemental Oil And Gas Information [Abstract] |  |  |
Balance, beginning of year | $ 38,708 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | $ 45,354 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | $ 51,909 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves
Sales, net of production costs and taxes | (8,385)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts | (10,471)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts | (14,275)us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts
Discoveries and extensions, net of costs | 4,231 us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts | 4,047 us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts | 6,967 us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts
Purchase of reserves in place |  |  |
Sale of reserves in place |  | (767)us-gaap_DecreaseDueToSalesOfMineralsInPlace |
Net changes in prices and production costs | (829)us-gaap_NetIncreaseDecreaseInSalesAndTransferPricesAndProductionCosts | (1,277)us-gaap_NetIncreaseDecreaseInSalesAndTransferPricesAndProductionCosts | (6,067)us-gaap_NetIncreaseDecreaseInSalesAndTransferPricesAndProductionCosts
Revisions of quantity estimates | (6,610)us-gaap_RevisionsOfPreviousQuantityEstimates | (4,306)us-gaap_RevisionsOfPreviousQuantityEstimates | (9,883)us-gaap_RevisionsOfPreviousQuantityEstimates
Previously estimated development cost incurred during the year | 508 us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod | 3,149 us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod | 8,760 us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod
Changes in future development costs | (1,913)us-gaap_IncreaseDecreaseInEstimatedFutureDevelopmentCosts | (1,392)us-gaap_IncreaseDecreaseInEstimatedFutureDevelopmentCosts | (1,919)us-gaap_IncreaseDecreaseInEstimatedFutureDevelopmentCosts
Changes in production rates (timing) and other | 1,312 tgc_ChangesInProductionRatesAndOther | 368 tgc_ChangesInProductionRatesAndOther | (5,657)tgc_ChangesInProductionRatesAndOther
Accretion of discount | 4,247 us-gaap_AccretionOfDiscount | 4,593 us-gaap_AccretionOfDiscount | 6,223 us-gaap_AccretionOfDiscount
Net change in income taxes | 3,262 us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves | (590)us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves | 9,296 us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves
Balance, end of year | $ 34,531 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | $ 38,708 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | $ 45,354 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves

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- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of passage of time. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62500-109447 + Details
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