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Acquisitions And Dispositions (Narrative) (Details) $ in Thousands, a in Millions |  |  |  | 1 Months Ended | 12 Months Ended |
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Nov. 22, 2016 | Mar. 14, 2016 USD ($) | Jan. 01, 2014 | Apr. 30, 2017 USD ($) | Dec. 31, 2016 USD ($) item | Oct. 31, 2014 item | Nov. 30, 2006 a item | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Apr. 30, 2014 USD ($)
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |
Proceeds from the sale of oil and gas properties |  |  |  |  |  |  |  | $ 250 | $ 830 | $ 398 |
Gain from sale of property |  |  |  |  |  |  |  | 300 |  |  |
Allowance for accounts with partners |  |  |  |  | $ 500 |  |  | $ 500 | 500 |  |
Offshore Gabon [Member] |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |
Production license agreement term extended by government |  |  |  |  |  |  |  | 5 years |  |  |
Hefley Field [Member] |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |
Proceeds received from sale of property |  |  |  |  | $ 800 |  |  |  |  |  |
Number of wells, interest for sale | item |  |  |  |  | 2 |  |  |  |  |  |
East Poplar Dome Field [Member] |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |
Proceeds from the sale of oil and gas properties |  |  |  | $ 300 |  |  |  |  |  |  |
Joint Operating With Republic Of Angola [Member] |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |
Primary term of the production sharing contract |  |  |  |  |  |  |  | 4 years |  |  |
Optional term of extension of production sharing contract |  |  |  |  |  |  |  | 3 years |  |  |
Area under acquire property exploration rights agreement term (acres) | a |  |  |  |  |  |  | 1.4 |  |  |  |
Number of exploration wells | item |  |  |  |  |  |  | 2 |  |  |  |
Number Of Additional Exploration Wells | item |  |  |  |  |  | 2 |  |  |  |  |
Joint operation agreement related to third party in working interest percentage |  |  |  |  |  |  | 40.00% |  |  |  |
Additional joint operation agreement related to third party in working interest percentage |  |  |  |  |  |  | 10.00% |  |  |  |
Stipulated payment for each exploration well, under PSA terms |  |  |  |  |  |  |  | $ 10,000 |  |  |
Drilling commitment, net |  |  |  |  |  |  |  | 5,000 |  |  |
Liability for the penalty |  |  |  |  | $ 15,000 |  |  | $ 15,000 | 15,000 |  |
Allowance for accounts with partners |  |  |  |  |  |  |  |  |  |  | $ 7,600
Working interest ownership other, percentage |  |  | 40.00% |  |  |  |  |  |  |  |
Sojitz [Member] |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percentage of working interest | 2.98% |  |  |  |  |  |  |  |  |  |
Percentage of participating interest | 3.23% |  |  |  |  |  |  |  |  |  |
Actual impact on revenue from acquisition |  |  |  |  |  |  |  |  | $ 200 |  |
Sonangol P&P [Member] |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |
Payment from joint venture partners |  | $ 19,000 |  |  |  |  |  |  |  |  |
Reversal of allowance |  | 7,600 |  |  |  |  |  |  |  |  |
Interest income |  | $ 3,200 |  |  |  |  |  |  |  |  |

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