Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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)	(12,773)	985
Ending Balance	2,091,777	2,065,588
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)	(12,773)	985
Ending Balance	(54,714)	(32,144)
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)	(13,297)	223
Ending Balance	(28,248)	(7,708)
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
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)	524	308
Ending Balance	(26,466)	(24,436)
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)	31	459
Ending Balance	1,846,955	1,799,769
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)	31	459
Ending Balance	(1,188)	137
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
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)	31	5
Ending Balance	$ (1,188)	$ 137