Electric utility segment - HECO Capital Trust III (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
VIE, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Investments	$ 51,500		$ 51,500
Investment income, interest	$ 800	$ 2,500
Trust Preferred Securities Subject to Mandatory Redemption | Hawaiian Electric Company
Variable Interest Entity [Line Items]
Dividend rate percentage	6.50%
Trust Preferred Securities Subject to Mandatory Redemption | Hawaiian Electric Company | VIE, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Convertible preferred stock	$ 50,000		50,000
Distributions to holders of Trust Preferred Securities	800	2,400
Trust Common Securities | Hawaiian Electric Company | VIE, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Convertible preferred stock	1,500		$ 1,500
Common dividends on the trust common securities	$ 25	$ 75