Reconciliation of income and expenses (Details 10) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of tax	[1]									$ (3,783)	$ (300,354)	$ (834,080)
Loss from discontinued operations attributable to noncontrolling interest										0	(131,691)	(35,256)
Loss from discontinued operations attributable to the Company		$ (82)	$ (2,198)	$ (3,190)	$ 1,687	$ (816)	$ (5,400)	$ (155,451)	$ (6,996)
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										465	123,024	363,115
Operating expenses										(4,607)	513,813	1,666,941
Operating income (loss)										5,072	(390,789)	(1,303,826)
Other expense										(13)
Other income											306	3,149
Interest expense										250	1,753	2,124
Income (loss) from discontinued operations before income taxes										4,809	(392,236)	(1,302,801)
Income taxes	[1]									8,592	(91,882)	(468,721)
Income (loss) from discontinued operations, net of tax										(3,783)	(300,354)	(834,080)
Loss from discontinued operations attributable to noncontrolling interest										0	(131,691)	(35,256)
Loss from discontinued operations attributable to the Company										(3,783)	(168,663)	(798,824)
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 loss attributable to the company										$ 6,900	$ (253,500)	$ (31,500)

[1] Includes eliminations for the presentation of income tax adjustments between continuing and discontinued operations.