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 ($)
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]        
Income (loss) from discontinued operations   $ (98,000) $ 5,411,000 $ (496,000)
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   93,000 344,000 467,000
Total operating costs, expenses and (recovery)   93,000 (6,849,000) 467,000
Operating income (loss)   (93,000) 6,849,000 (467,000)
Other, net   (5,000)   (29,000)
Total other expense   (5,000)   (29,000)
Income (loss) from discontinued operations before income taxes   (98,000) 6,849,000 (496,000)
Income tax expense (benefit)     1,438,000  
Income (loss) from discontinued operations $ 5,700,000 $ (98,000) $ 5,411,000 $ (496,000)