Electric utility segment - Rate proceedings (Details) - USD ($) $ in Thousands	Oct. 01, 2019	Aug. 21, 2019	Mar. 18, 2019	Dec. 14, 2018
Hawaiian Electric (parent only)
Regulatory Projects and Legal Obligations [Line Items]
Stipulated ROACE rate		10.50%
General rate increase, revenue		$ 77,600
General rate increase, revenue, percent		4.10%
Assumptions on rate of return, return on average common equity, percentage decrease		8.00%
Maui Electric
Regulatory Projects and Legal Obligations [Line Items]
Interim general rate increase granted			$ 12,200
Effective interest rate of return			7.43%
Stipulated ROACE rate			9.50%
Common equity capitalization rate			57.00%
Rate Base			$ 454,000
Risk sharing percentage, ratepayer			98.00%
Risk sharing percentage, utility			2.00%
Maximum exposure cap			$ 600
HELCO
Regulatory Projects and Legal Obligations [Line Items]
Stipulated ROACE rate				10.50%
General rate increase, revenue				$ 13,400
General rate increase, revenue, percent				3.40%
Assumptions on rate of return, return on average common equity, percentage decrease				8.30%
HELCO | Subsequent Event
Regulatory Projects and Legal Obligations [Line Items]
Interim general rate increase granted	$ 2,790
Stipulated ROACE rate	9.50%
Common equity capitalization rate	58.00%
Amortization term	40 years
Final rate increase	10.50%