Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	$ 2,162,280	$ 2,097,386
Current period other comprehensive income (loss)	9,241	(12,773)
Ending Balance	2,183,515	2,091,777
AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(50,610)	(41,941)
Current period other comprehensive income (loss)	9,241	(12,773)
Ending Balance	(41,369)	(54,714)
Net unrealized gains (losses) on securities
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(24,423)	(14,951)
Current period other comprehensive income (loss)	9,439	(13,297)
Ending Balance	(14,984)	(28,248)
Unrealized gains (losses) on derivatives
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(436)	0
Current period other comprehensive income (loss)	(403)	0
Ending Balance	(839)	0
Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(25,751)	(26,990)
Current period other comprehensive income (loss)	205	524
Ending Balance	(25,546)	(26,466)
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	1,957,641	1,845,283
Current period other comprehensive income (loss)	24	31
Ending Balance	1,964,478	1,846,955
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	99	(1,219)
Current period other comprehensive income (loss)	24	31
Ending Balance	123	(1,188)
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	99	(1,219)
Current period other comprehensive income (loss)	24	31
Ending Balance	$ 123	$ (1,188)