Income taxes - Income Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Expense (Benefit) [Line Items]
Amount at the federal statutory income tax rate	$ 53,437	$ 96,796	$ 130,844
Increase (decrease) resulting from:
State income taxes, net of federal income tax benefit	11,832	9,789	13,915
Net deferred tax asset (liability) adjustment related to the Tax Act	(9,540)	13,420	0
Other, net	(4,932)	(10,612)	(21,064)
Federal and state taxes	$ 50,797	$ 109,393	$ 123,695
Effective income tax rate	20.00%	39.60%	33.10%
Hawaiian Electric Company, Inc. and Subsidiaries
Income Tax Expense (Benefit) [Line Items]
Amount at the federal statutory income tax rate	$ 37,889	$ 71,801	$ 80,190
Increase (decrease) resulting from:
State income taxes, net of federal income tax benefit	8,080	7,584	8,494
Net deferred tax asset (liability) adjustment related to the Tax Act	(9,285)	9,168	0
Other, net	(1,906)	(5,354)	(3,883)
Federal and state taxes	$ 34,778	$ 83,199	$ 84,801
Effective income tax rate	19.30%	40.60%	37.00%