Annual report pursuant to Section 13 and 15(d)

Dispositions (Summarized Results of Discontinued Operations) (Details)

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Dispositions (Summarized Results of Discontinued Operations) (Details) - USD ($)
3 Months Ended 12 Months Ended
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Income (loss) from discontinued operations $ (37,000) $ (61,000) $ (162,000) $ 5,671,000 $ (80,000) $ (21,000) $ (343,000) $ (52,000) $ 5,411,000 $ (496,000) $ (621,000)
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]                      
Gain on settlement of drilling obligation                 (7,193,000)    
General and administrative expense                 344,000 467,000 615,000
Total operating costs, expenses and (recovery)                 (6,849,000) 467,000 615,000
Operating income (loss)                 6,849,000 (467,000) (615,000)
Other, net                   (29,000) (3,000)
Total other income (expense)                   (29,000) (3,000)
Income (loss) from discontinued operations before income taxes                 6,849,000 (496,000) (618,000)
Income tax expense                 1,438,000   3,000
Income (loss) from discontinued operations       $ 5,700,000         $ 5,411,000 $ (496,000) $ (621,000)