Shareholders' equity - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	$ 534	$ 346	$ 1,581	$ 1,457
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	28	22	85	521
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	5,259	3,942	15,755	11,793
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	4,753	3,618	14,259	10,857
Impact of D&Os of the PUC included in regulatory assets
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	(4,725)	(3,596)	(14,174)	(10,790)
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	(4,725)	(3,596)	(14,174)	(10,790)
Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on derivatives | Forward commitments
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	0	0	0	454
Reclassification out of Accumulated Other Comprehensive Income | Unrealized gains (losses) on derivatives | Forward commitments | Hawaiian Electric Company, Inc. and Subsidiaries
Reclassifications out of accumulated other comprehensive income/(loss)
Total reclassifications	$ 0	$ 0	$ 0	$ 454