Shareholders' equity - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	$ 548	$ 205
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	26	24
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	5,706	2,503
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	5,184	2,322
Impact of D&Os of the PUC included in regulatory assets
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	(5,158)	(2,298)
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	$ (5,158)	$ (2,298)