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Organization and Accounting Policies (Narrative) (Details) |  |  | 3 Months Ended | 9 Months Ended | 24 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Jun. 20, 2026 | Feb. 25, 2021 | Sep. 30, 2021 USD ($) / $ | Sep. 30, 2020 USD ($) | Sep. 30, 2021 USD ($) / $ | Sep. 30, 2020 USD ($) | Dec. 31, 2020 USD ($) / $ | Feb. 24, 2021
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Impairment of proved crude oil and natural gas properties |  |  | $ 0 | $ 0 | $ 0 | $ 30,625,000 |  |
Receivable balance, gross, noncurrent |  |  | $ 9,600,000 |  | $ 9,600,000 |  | $ 4,500,000 |
Abandonment funding payments missed |  |  |  |  |  |  | $ 2,900,000 |
Exchange rate | / $ |  |  | 566.0 |  | 566.0 |  | 534.8 |
Transfers between levels |  |  |  |  | $ 0 | $ 0 |  |
Office and Miscellaneous Equipment [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Estimated useful life of assets |  |  |  |  | 5 years |  |  |
Leasehold Improvements [Member] | Minimum [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Estimated useful life of assets |  |  |  |  | 5 years |  |  |
Leasehold Improvements [Member] | Maximum [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Estimated useful life of assets |  |  |  |  | 7 years |  |  |
Consortium [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Receivable balance, gross, noncurrent |  |  | $ 14,400,000 |  | $ 14,400,000 |  | $ 13,400,000 |
Prior Production Sharing Contract, Through September 17, 2018 [Member] | Government Of Gabon [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Monthly royalty rate, based on production at the published price |  |  |  |  | 13.00% |  |  |
Production Sharing Contract, September 17, 2018 Through September 16, 2028 [Member] | Government Of Gabon [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Monthly royalty rate, based on production at the published price |  |  |  |  | 13.00% |  |  |
Etame Marine Block [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Impairment of proved crude oil and natural gas properties |  |  |  | $ 30,600,000 |  |  |  |
Working interest ownership, percentage |  | 58.80% |  |  |  |  |  | 31.10%
Etame Marine Block [Member] | Sasol Gabon S.A. [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Increase (decrease) in working interest ownership percentage |  | 27.80% |  |  |  |  |  |
Etame Marine Block [Member] | Prior Production Sharing Contract, Through September 17, 2018 [Member] | Consortium [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Working interest ownership, percentage |  |  | 7.50% |  | 7.50% |  |  |
Etame Marine Block [Member] | Production Sharing Contract, September 17, 2018 Through September 16, 2028 [Member] | Government Of Gabon [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Working interest ownership, percentage |  |  | 7.50% |  | 7.50% |  |  |
Etame Marine Block [Member] | Scenario, Forecast [Member] | Production Sharing Contract, September 17, 2018 Through September 16, 2028 [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Increase (decrease) in working interest ownership percentage | (1.60%) |  |  |  |  |  |  |
Etame Marine Block [Member] | Scenario, Forecast [Member] | Production Sharing Contract, September 17, 2018 Through September 16, 2028 [Member] | Government Of Gabon [Member] |  |  |  |  |  |  |  |
Organization And Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Increase (decrease) in working interest ownership percentage | 2.50% |  |  |  |  |  |  |
Working interest ownership, percentage | 10.00% |  |  |  |  |  |  |

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