Income taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Expense (Benefit) [Line Items]
Reconciliation percentage of amount of income taxes computed at federal statutory rate	35.00%	35.00%	35.00%
Unrecognized tax benefits	$ 3,800	$ 3,600	$ 0	$ 900
Credit adjustments to interest expense on income taxes	200	100	(1,700)
Amount of accrued interest related to uncertain tax positions	300	100
Expected increase in depreciation expense	$ 126,000
Renewable energy investment tax credit, percent	30.00%
Hawaiian Electric Company, Inc. and Subsidiaries
Income Tax Expense (Benefit) [Line Items]
Unrecognized tax benefits	$ 3,800	3,600	0	$ 500
Credit adjustments to interest expense on income taxes	30	100	$ (700)
Amount of accrued interest related to uncertain tax positions	100	$ 100
Hawaiian Electric Company, Inc. and Subsidiaries | Federal Tax Authority
Income Tax Expense (Benefit) [Line Items]
Net operating loss	9,000
Unrecognized tax benefits	3,000
Hawaiian Electric Company, Inc. and Subsidiaries | Federal Tax Authority | General Business Tax Credit Carryforward
Income Tax Expense (Benefit) [Line Items]
Federal general business credit carryforward	$ 3,000