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Commitments And Contingencies (Narrative) (Details) $ in Thousands | 1 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Apr. 30, 2018 USD ($) | Sep. 30, 2018 USD ($) item | Sep. 25, 2018 USD ($) | Dec. 31, 2017 USD ($)
Commitments And Contingencies [Line Items] |  |  |  |
Number of drilled wells required by agreement | item |  | 2 |  |
Number of appraisal wells required by agreement | item |  | 2 |  |
Estimated costs of wells, gross amount |  | $ 61,200 |  |
Estimated costs of wells |  | 20,500 |  |
Estimated costs of technical studies |  | 1,300 |  |
Estimated costs of technical studies, net |  | 400 |  |
Abandonment Funding |  | 10,808 |  | $ 10,808
Abandonment cost related to annual funding |  | 61,100 |  |
Abandonment cost related to annual funding, net |  | 19,000 |  |
Accrued liabilities and other |  | 17,662 |  | 12,991
Potential Fees From Customs Audits [Member] |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |
Accrued liabilities and other |  | 1,300 |  | 1,300
Gabon [Member] |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |
Accrued liabilities, end of drilling activities, gross amount |  | 5,000 |  |
Accrued liabilities, end of drilling activities |  | 1,700 |  |
Abandonment Funding |  | 10,800 |  |
Contractual obligation |  |  | $ 21,800 |
Abandonment funding, gross |  | $ 34,800 |  |
Accrued estimated settlement |  |  |  | 500
Tax examination settlement payment | $ 200 |  |  |
Tax penalties | $ 200 |  |  |
Offshore Gabon [Member] |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |
Production License Agreement Term Extended By Government |  | 5 years |  |
Percentage of annual funding over seven years |  | 12.14% |  |
Funding period for initial rate |  | 7 years |  |
Second funding period of production license |  | 3 years |  |
Percentage of annual funding over last three years |  | 5.00% |  |
Funding period abandonment funding |  | 10 years |  |
Number of contract extension periods | item |  | 2 |  |
FPSO Charter [Member] |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |
Number of extensions | item |  | 2 |  |
Period of charter (in years) |  | 1 year |  |
Percentage of share in charter payment |  | 31.10% |  |
Share in charter payment, approximate annual amount |  | $ 9,700 |  |
Liabilities, guarantees' fair value |  | 400 |  | 500
Contractual obligation |  | $ 61,800 |  | $ 85,200

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