Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			$ 2,097,386	$ 2,066,753
Current period other comprehensive income (loss)	$ (4,589)	$ 554	(21,187)	3,909
Ending Balance	2,132,045	2,103,022	2,132,045	2,103,022
AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(41,941)	(33,129)
Current period other comprehensive income (loss)			(21,187)	3,909
Ending Balance	(63,128)	(29,220)	(63,128)	(29,220)
Net unrealized gains (losses) on securities
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(14,951)	(7,931)
Current period other comprehensive income (loss)			(22,768)	2,452
Ending Balance	(37,719)	(5,479)	(37,719)	(5,479)
Unrealized gains (losses) on derivatives
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			0	(454)
Current period other comprehensive income (loss)			0	454
Ending Balance	0	0	0	0
Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(26,990)	(24,744)
Current period other comprehensive income (loss)			1,581	1,003
Ending Balance	(25,409)	(23,741)	(25,409)	(23,741)
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			1,845,283	1,799,787
Current period other comprehensive income (loss)	28	22	85	521
Ending Balance	1,876,237	1,829,075	1,876,237	1,829,075
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(1,219)	(322)
Current period other comprehensive income (loss)			85	521
Ending Balance	(1,134)	199	(1,134)	199
Hawaiian Electric Company, Inc. and Subsidiaries | Unrealized gains (losses) on derivatives
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			0	(454)
Current period other comprehensive income (loss)			0	454
Ending Balance	0	0	0	0
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(1,219)	132
Current period other comprehensive income (loss)			85	67
Ending Balance	$ (1,134)	$ 199	$ (1,134)	$ 199