Long-Term Debt And Lease Liabilities (Narrative) (Details)	3 Months Ended
Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Borrowing rate	6.00%
Office [Member]
Debt Instrument [Line Items]
Term of contract	39 months
Lease renewal term	36 months
Prosperity Bank [Member]
Debt Instrument [Line Items]
Interest rate	6.00%
Credit facility current borrowing capacity	$ 3,000,000
Credit facility amount outstanding	0	$ 0
Credit limit	2,740,000
Prosperity Bank [Member] \| Loans And Letters Of Credit [Member]
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity	$ 50,000,000
Maximum [Member]
Debt Instrument [Line Items]
Borrowing rate	6.50%
Maximum [Member] \| Vehicles [Member]
Debt Instrument [Line Items]
Term of contract	36 months
Discount rate	6.50%
Maximum [Member] \| Prosperity Bank [Member]
Debt Instrument [Line Items]
Funded debt to EBITDA	3.5
Minimum [Member]
Debt Instrument [Line Items]
Borrowing rate	5.00%
Minimum [Member] \| Vehicles [Member]
Debt Instrument [Line Items]
Term of contract	18 months
Discount rate	5.00%
Minimum [Member] \| Prosperity Bank [Member]
Debt Instrument [Line Items]
Current ratio	1
Interest coverage	3.0

Line Of Credit Facility, Covenant, Current Ratio

No definition available.

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- Definition

Line Of Credit Facility, Covenant, Funded Debt To Ebitda

+ References

No definition available.

+ Details

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- Definition

Line Of Credit Facility, Covenant, Interest Coverage

+ References

No definition available.

+ Details

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Namespace Prefix:	tgc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

The average effective interest rate during the reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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-Subparagraph (SX 210.5-02.22(a)(1))
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+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of lessee's finance lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

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-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Discount rate used by lessee to determine present value of operating lease payments.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)(3)
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Balance Type:	na
Period Type:	instant

- Definition

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Maximum amount borrowed under the credit facility at any time during the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	instant

- Details

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