Reconciliation of income and expenses (Details 7) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations									$ 2,932,000	$ (3,783,000)	$ (300,354,000)
Loss from discontinued operations attributable to noncontrolling interest									0	0	(131,691,000)
Income (loss) from discontinued operations attributable to the Company	$ 2,846,000	$ (118,000)	$ (273,000)	$ 477,000	$ (82,000)	$ (2,198,000)	$ (3,190,000)	$ 1,687,000
Discontinued operations, held-for-sale or disposed by sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues									(459,000)	465,000	123,024,000
Operating expenses									921,000	(4,607,000)	513,813,000
Operating income (loss)									(1,380,000)	5,072,000	(390,789,000)
Other income									12,000		306,000
Other expense										(13,000)
Interest expense									575,000	250,000	1,753,000
Income (loss) from discontinued operations before income taxes									(1,943,000)	4,809,000	(392,236,000)
Income taxes									(4,875,000)	8,592,000	(91,882,000)
Income (loss) from discontinued operations									2,932,000	(3,783,000)	(300,354,000)
Loss from discontinued operations attributable to noncontrolling interest									0	0	(131,691,000)
Income (loss) from discontinued operations attributable to the Company									2,932,000	(3,783,000)	(168,663,000)
Refining [Member] | Discontinued operations, held-for-sale or disposed by sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pretax income (loss) attributable to the company									$ (7,000)	$ 6,900,000	$ (253,500,000)