Deferred tax reconciliation (Details 6) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Change in net deferred income tax liability from the preceding table	$ 76,498
Deferred taxes associated with other comprehensive loss	1,631
Deferred taxes associated with TCJA enactment for regulated activities	(11,904)
Other	(2,810)
Deferred income taxes	$ 63,415	$ 59,735	$ (25,423)