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
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Oil And Gas Information [Abstract]
Balance, beginning of year	$ 38,708	$ 45,354	$ 51,909
Sales, net of production costs and taxes	(8,385)	(10,471)	(14,275)
Discoveries and extensions, net of costs	4,231	4,047	6,967
Purchase of reserves in place
Sale of reserves in place		(767)
Net changes in prices and production costs	(829)	(1,277)	(6,067)
Revisions of quantity estimates	(6,610)	(4,306)	(9,883)
Previously estimated development cost incurred during the year	508	3,149	8,760
Changes in future development costs	(1,913)	(1,392)	(1,919)
Changes in production rates (timing) and other	1,312tgc_ChangesInProductionRatesAndOther	368tgc_ChangesInProductionRatesAndOther	(5,657)tgc_ChangesInProductionRatesAndOther
Accretion of discount	4,247us-gaap_AccretionOfDiscount	4,593us-gaap_AccretionOfDiscount	6,223us-gaap_AccretionOfDiscount
Net change in income taxes	3,262	(590)	9,296
Balance, end of year	$ 34,531	$ 38,708	$ 45,354

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

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Supplemental Oil And Gas Information [Abstract]

Balance, beginning of year

$ 38,708us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves

$ 45,354us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves

$ 51,909us-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

4,231us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts

4,047us-gaap_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts

6,967us-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

508us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod

3,149us-gaap_PreviouslyEstimatedDevelopmentCostsIncurredDuringPeriod

8,760us-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

1,312tgc_ChangesInProductionRatesAndOther

368tgc_ChangesInProductionRatesAndOther

(5,657)tgc_ChangesInProductionRatesAndOther

Accretion of discount

4,247us-gaap_AccretionOfDiscount

4,593us-gaap_AccretionOfDiscount

6,223us-gaap_AccretionOfDiscount

Net change in income taxes

3,262us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves

(590)us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves

9,296us-gaap_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves

Balance, end of year

$ 34,531us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves

$ 38,708us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves

$ 45,354us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves

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