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, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Loss from discontinued operations $ (103) $ (174) $ (168) $ (176) $ (286) $ (15,783) $ (20) $ 7,806 $ (621) $ (8,283) $ (38,102)
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 36,044
Depreciation, depletion and amortization                   9 12
General and administrative expense                 615 1,269 2,535
Bad debt recovery and other                   (7,629)  
Total operating costs, expenses and (recovery)                 615 8,786 38,591
Other operating loss, net                   (172) (1,856)
Operating loss                 (615) (8,958) (40,447)
Interest income                   3,201  
Other, net                 (3) 552 2,345
Total other income (expense)                 (3) 3,753 2,345
Loss from discontinued operations before income taxes                 (618) (5,205) (38,102)
Income tax expense                 3 3,078  
Loss from discontinued operations                 $ (621) $ (8,283) $ (38,102)