Discontinued Operations and Assets Held for Sale (Major Categories of Assets and Liabilities Reflected as Held for Sale) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accounts receivable	$ 267,209	$ 357,099
Total current assets held for sale	23,248	27,070
Accounts payable	584,025	784,975
Total current liabilities associated with assets held for sale	3,270	2,776
Asset retirement obligation - Seal asset	747,602	681,528
Total non-current liabilities associated with assets held for sale		85,900
UK Refining And Marketing Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash	17,030	4,126
Accounts receivable	6,218	22,944
Total current assets held for sale	23,248	27,070
Accounts payable	605	270
Refinery decommissioning cost	2,665	2,506
Total current liabilities associated with assets held for sale	$ 3,270	2,776
Asset retirement obligation - Seal asset		$ 85,900