Acquisitions And Dispositions (Assets And Liabilities Attributable To Discontinued Operations) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total current assets	$ 3,030	$ 2,836
Total current liabilities	15,002	15,347
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 with partners	3,030	2,836
Total current assets	3,030	2,836
Total assets	3,030	2,836
Accounts payable	1	158
Accrued liabilities and other	15,001	15,189
Total current liabilities	15,002	15,347
Total liabilities	$ 15,002	$ 15,347