Acquisitions and Dispositions (Assets and Liabilities Attributable to Discontinued Operations) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total current liabilities	$ 7	$ 350
Joint Operating With Republic Of Angola [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accounts payable		8
Accrued liabilities and other	7	342
Total current liabilities	7	350
Total liabilities	$ 7	$ 350