Deferred tax reconciliation (Details 6) - USD ($) $ in Thousands	12 Months Ended
	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)