Annual report pursuant to Section 13 and 15(d)

Acquisitions And Dispositions (Summarized Results Of Discontinued Operations) (Details)

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Acquisitions And Dispositions (Summarized Results Of Discontinued Operations) (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Loss from discontinued operations $ (80) $ (21) $ (343) $ (52) $ (103) $ (174) $ (168) $ (176) $ (496) $ (621) $ (8,283)
Discontinued Operations [Member] | Joint Operating With Republic Of Angola [Member]                      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Exploration expense                     15,137
Depreciation, depletion and amortization                     9
General and administrative expense                 467 615 1,269
Bad debt recovery and other                     (7,629)
Total operating costs, expenses and (recovery)                 467 615 8,786
Other operating loss, net                     (172)
Operating loss                 (467) (615) (8,958)
Interest income                     3,201
Other, net                 (29) (3) 552
Total other income (expense)                 (29) (3) 3,753
Loss from discontinued operations before income taxes                 (496) (618) (5,205)
Income tax expense                   3 3,078
Loss from discontinued operations                 $ (496) $ (621) $ (8,283)