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Tax reform (Details 3) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 | Dec. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
TCJA revaluation related to accumulated other comprehensive loss balance |  | $ (39,500) | $ (42) | $ 7,735 | $ 0
Deferred tax liabilities, regulatory assets |  |  | $ 13,776 |  |
Other comprehensive income (loss) [Member] |  |  |  |  |
TCJA revaluation related to accumulated other comprehensive loss balance |  | 7,700 |  |  |
Discontinued operations, held-for-sale [Member] |  |  |  |  |
TCJA revaluation related to accumulated other comprehensive loss balance |  | 1,000 |  |  |
Stranded costs [Member] |  |  |  |  |
Deferred tax liabilities, regulatory assets | $ (4,200) | $ 285,500 |  |  |

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