Shareholders' equity - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassifications out of accumulated other comprehensive income/(loss)
Revenues	$ 771,535	$ 768,048	$ 2,148,635	$ 2,099,199
Total reclassifications	(356)	534	54	1,581
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	26	28	73	85
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	2,615	5,259	7,621	15,755
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost | Hawaiian Electric Company, Inc. and Subsidiaries
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	2,519	4,753	7,162	14,259
Impact of D&Os of the PUC included in regulatory assets
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	(2,493)	(4,725)	(7,089)	(14,174)
Impact of D&Os of the PUC included in regulatory assets | Hawaiian Electric Company, Inc. and Subsidiaries
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	(2,493)	(4,725)	(7,089)	(14,174)
Bank
Reclassifications out of accumulated other comprehensive income/(loss)
Revenues	83,201	80,496	247,940	233,019
Bank | Reclassification out of Accumulated Other Comprehensive Income [Member] | Net realized gains on securities included in net income
Reclassifications out of accumulated other comprehensive income/(loss)
Revenues	$ 478	$ 0	$ 478	$ 0