Assets Held for Sale and Discontinued Operations (Results of Operations Associated with Discontinued Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
(Loss) income from discontinued operations	$ (706)	$ (778)	$ (600)	$ (6,907)
Discontinued Operation | U.K. and U.S. Refining And Marketing Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	144	0	801	4,074
Other costs and expenses (benefits)	850	778	1,401	10,981
(Loss) income before taxes	(706)	(778)	(600)	(6,907)
Income tax expense	0	0	0	0
(Loss) income from discontinued operations	$ (706)	$ (778)	$ (600)	$ (6,907)
Discontinued operations, held-for-sale or disposed of by sale | King's Quay Floating Production System
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total current assets associated with assets held for sale					$ 250,100