Income taxes - Income Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Expense (Benefit) [Line Items]
Amount at the federal statutory income tax rate	$ 50,531	$ 56,996	$ 53,437
Increase (decrease) resulting from:
State income taxes, net of federal income tax benefit	9,448	11,658	11,832
Net deferred tax asset (liability) adjustment related to the Tax Act	(11,267)	(9,255)	(9,540)
Other, net	(7,802)	(7,762)	(4,932)
Total	$ 40,910	$ 51,637	$ 50,797
Effective income tax rate	17.00%	19.00%	20.00%
Hawaiian Electric Company, Inc. and Subsidiaries
Income Tax Expense (Benefit) [Line Items]
Amount at the federal statutory income tax rate	$ 44,468	$ 41,399	$ 37,889
Increase (decrease) resulting from:
State income taxes, net of federal income tax benefit	9,658	8,703	8,080
Net deferred tax asset (liability) adjustment related to the Tax Act	(11,267)	(9,255)	(9,285)
Other, net	(2,441)	(2,542)	(1,906)
Total	$ 40,418	$ 38,305	$ 34,778
Effective income tax rate	19.10%	19.40%	19.30%