Income taxes - Components of Income Taxes Attributable to Net Income for Common Stock (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Federal
Current	$ 28,736	$ 42,903	$ 61,534
Deferred	(4,353)	(6,099)	33,967
Deferred tax credits, net	13,410	(12)	(20)
Federal taxes	37,793	36,792	95,481
State
Current	10,472	17,361	10,076
Deferred	(10,732)	(3,269)	3,868
Deferred tax credits, net	14,104	(87)	(32)
State taxes	13,844	14,005	13,912
Federal and state taxes	51,637	50,797	109,393
Hawaiian Electric Company, Inc. and Subsidiaries
Federal
Current	21,751	29,649	36,267
Deferred	(7,793)	(5,245)	35,229
Deferred tax credits, net	13,155	(12)	(20)
Federal taxes	27,113	24,392	71,476
State
Current	5,579	13,210	8,947
Deferred	(8,491)	(2,737)	2,808
Deferred tax credits, net	14,104	(87)	(32)
State taxes	11,192	10,386	11,723
Federal and state taxes	$ 38,305	$ 34,778	$ 83,199