Income taxes - Income Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Expense (Benefit) [Line Items]
Amount at the federal statutory income tax rate	$ 56,996	$ 53,437	$ 96,796
Increase (decrease) resulting from:
State income taxes, net of federal income tax benefit	11,658	11,832	9,789
Net deferred tax asset (liability) adjustment related to the Tax Act	(9,255)	(9,540)	13,420
Other, net	(7,762)	(4,932)	(10,612)
Federal and state taxes	$ 51,637	$ 50,797	$ 109,393
Effective income tax rate	19.00%	20.00%	39.60%
Hawaiian Electric Company, Inc. and Subsidiaries
Income Tax Expense (Benefit) [Line Items]
Amount at the federal statutory income tax rate	$ 41,399	$ 37,889	$ 71,801
Increase (decrease) resulting from:
State income taxes, net of federal income tax benefit	8,703	8,080	7,584
Net deferred tax asset (liability) adjustment related to the Tax Act	(9,255)	(9,285)	9,168
Other, net	(2,542)	(1,906)	(5,354)
Federal and state taxes	$ 38,305	$ 34,778	$ 83,199
Effective income tax rate	19.40%	19.30%	40.60%