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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)

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