Discontinued Operations and Assets Held for Sale (Major Categories of Assets and Liabilities Reflected as Held for Sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accounts receivable	$ 258,366	$ 243,472
Total current assets held for sale	21,667	22,929
Accounts payable	632,072	595,916
Total current liabilities associated with assets held for sale	3,146	3,530
UK Refining And Marketing Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash	14,609	16,631
Accounts receivable	7,058	6,298
Total current assets held for sale	21,667	22,929
Accounts payable	488	837
Refinery decommissioning cost	2,658	2,693
Total current liabilities associated with assets held for sale	$ 3,146	$ 3,530