Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	$ 2,280,260	$ 2,162,280
Current period other comprehensive income (loss)	18,212	9,241
Ending Balance	2,276,505	2,183,515
AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(20,039)	(50,610)
Current period other comprehensive income (loss)	18,212	9,241
Ending Balance	(1,827)	(41,369)
Net unrealized gains (losses) on securities
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	2,481	(24,423)
Current period other comprehensive income (loss)	19,448	9,439
Ending Balance	21,929	(14,984)
Unrealized gains (losses) on derivatives
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(1,613)	(436)
Current period other comprehensive income (loss)	(1,784)	(403)
Ending Balance	(3,397)	(839)
Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(20,907)	(25,751)
Current period other comprehensive income (loss)	548	205
Ending Balance	(20,359)	(25,546)
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	2,047,352	1,957,641
Current period other comprehensive income (loss)	26	24
Ending Balance	2,044,499	1,964,478
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(1,279)	99
Current period other comprehensive income (loss)	26	24
Ending Balance	(1,253)	123
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(1,279)	99
Current period other comprehensive income (loss)	26	24
Ending Balance	$ (1,253)	$ 123