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
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Loss from discontinued operations $ (8,283) $ (38,102) $ (3,797)
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 1,707
Depreciation, depletion and amortization 9 12 12
General and administrative expense 1,269 2,535 2,082
Bad debt expense (recovery) and other (7,629)    
Total operating costs and expenses 8,786 38,591 3,801
Other operating loss, net (172) (1,856)  
Operating loss (8,958) (40,447) (3,801)
Interest income 3,201    
Other, net 552 2,345 4
Total other income 3,753 2,345 4
Loss from discontinued operations before income taxes (5,205) (38,102) (3,797)
Income tax expense 3,078    
Loss from discontinued operations $ (8,283) $ (38,102) $ (3,797)