Discontinued Operations and Assets Held for Sale (Major Categories of Assets and Liabilities Reflected as Held for Sale) (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]
Accounts receivable	$ 212,639	$ 243,472
Total current assets held for sale	22,696	22,929
Accounts payable	615,963	595,916
Total current liabilities associated with assets held for sale	3,160	3,530
UK Refining And Marketing Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash	16,380	16,631
Accounts receivable	6,316	6,298
Total current assets held for sale	22,696	22,929
Accounts payable	467	837
Refinery decommissioning cost	2,693	2,693
Total current liabilities associated with assets held for sale	$ 3,160	$ 3,530