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Acquisitions And Dispositions (Narrative) (Details) $ in Thousands, a in Millions |  |  |  | 1 Months Ended | 9 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Nov. 22, 2016 | Mar. 14, 2016 USD ($) | Jan. 01, 2014 | Apr. 30, 2017 USD ($) | Oct. 31, 2014 item | Apr. 30, 2014 USD ($) | Nov. 30, 2006 USD ($) a item | Sep. 30, 2017 USD ($) | Dec. 31, 2016 USD ($)
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Proceeds from sales of oil and gas properties |  |  |  |  |  |  |  | $ 250 |
Gain from sale of property |  |  |  |  |  |  |  | $ 300 |
Offshore Gabon [Member] |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Production license agreement term extended by government |  |  |  |  |  |  |  | 5 years |
East Poplar Dome Field [Member] |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Proceeds from sales of oil and gas properties |  |  |  | $ 300 |  |  |  |  |
Joint Operating With Republic Of Angola [Member] |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Production license agreement term |  |  |  |  |  |  | 4 years |  |
Production license agreement term extended by government |  |  |  |  |  |  | 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
Write off of bad debt |  |  |  |  |  | $ 7,600 |  |  |
Working interest ownership other, percentage |  |  | 40.00% |  |  |  |  |  |
Etame [Member] |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Percentage of working interest | 2.98% |  |  |  |  |  |  |  |
Percentage of participating interest | 3.23% |  |  |  |  |  |  |  |
Effective date of acquisition |  |  |  |  |  |  |  | Aug. 01, 2016 |
Sonangol P&P [Member] |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |
Payment from joint venture partners |  | $ 19,000 |  |  |  |  |  |  |
Write off of bad debt |  | 7,600 |  |  |  |  |  |  |
Interest income |  | $ 3,200 |  |  |  |  |  |  |

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