Reconciliation of income and expenses (Details 7) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations	$ 1,687	$ (18,036)
Loss from discontinued operations attributable to noncontrolling interest	0	(11,040)
Discontinued operations, held-for-sale or disposed of by sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues	105	47,976
Operating expenses	(6,577)	69,769
Operating income (loss)	6,682	(21,793)
Other income (expense)	(15)	204
Interest expense	0	922
Income (loss) from discontinued operations before income taxes	6,667	(22,511)
Income taxes	4,980	(4,475)
Income (loss) from discontinued operations	1,687	(18,036)
Loss from discontinued operations attributable to noncontrolling interest	0	(11,040)
Income (loss) from discontinued operations attributable to the Company	1,687	(6,996)
Discontinued operations, held-for-sale or disposed of by sale [Member] | Refining [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pretax income (loss) attributable to the Company	$ 6,900	$ (9,900)