Major classes of assets and liabilities (Details 4) - USD ($) $ in Thousands		Dec. 31, 2017		Dec. 31, 2016
Current assets:
Total current assets held for sale		$ 479		$ 14,391
Current liabilities:
Total current liabilities held for sale		11,993		9,924
Refining [Member] | Discontinued operations, held-for-sale or disposed by sale [Member]
Current assets:
Income taxes receivable		1,778		13,987
Total current assets held for sale		1,778		13,987
Total assets held for sale		1,778	[1]	13,987
Current liabilities:
Accounts payable		0		7,425
Total current liabilities held for sale		0		7,425
Deferred credits and other liabilities:
Deferred income taxes (b)	[2]	37		14
Total noncurrent liabilities held for sale		37		14
Total liabilities held for sale		$ 37		$ 7,439

[1] On the Company's Consolidated Balance Sheets, these amounts were reclassified to current income taxes payable and are reflected in current liabilities held for sale.

[2] On the Company's Consolidated Balance Sheets, these amounts were reclassified to noncurrent deferred income tax assetsand are reflected in noncurrent assets held for sale.