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Deferred tax reconciliation (Details 6) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Tax Disclosure [Abstract] |  |  |
Change in net deferred income tax liability from the preceding table | $ 82,814 |  |
Deferred taxes associated with other comprehensive income | (2,679) |  |
Deferred taxes associated with TCJA enactment for regulated activities | (13,776) |  |
Deferred taxes associated with acquisitions | (5,565) |  |
Other | (1,059) |  |
Deferred income taxes | $ 59,735 | $ (25,423) | $ (2,049)

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