Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	$ 2,208,586	$ 2,183,515	$ 2,162,280	$ 2,103,018	$ 2,091,777	$ 2,097,386	$ 2,162,280	$ 2,097,386
Current period other comprehensive income (loss)	3,297	13,699	9,241	(4,589)	(3,825)	(12,773)	26,237	(21,187)
Ending Balance	2,242,689	2,208,586	2,183,515	2,132,045	2,103,018	2,091,777	2,242,689	2,132,045
AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(27,670)	(41,369)	(50,610)	(58,539)	(54,714)	(41,941)	(50,610)	(41,941)
Current period other comprehensive income (loss)	3,297	13,699	9,241	(4,589)	(3,825)	(12,773)	26,237	(21,187)
Ending Balance	(24,373)	(27,670)	(41,369)	(63,128)	(58,539)	(54,714)	(24,373)	(63,128)
Net unrealized gains (losses) on securities
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(24,423)			(14,951)	(24,423)	(14,951)
Current period other comprehensive income (loss)							27,368	(22,768)
Ending Balance	2,945			(37,719)			2,945	(37,719)
Unrealized gains (losses) on derivatives
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(436)			0	(436)	0
Current period other comprehensive income (loss)							(1,663)	0
Ending Balance	(2,099)			0			(2,099)	0
Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance			(25,751)			(26,990)	(25,751)	(26,990)
Current period other comprehensive income (loss)							532	1,581
Ending Balance	(25,219)			(25,409)			(25,219)	(25,409)
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	1,971,762	1,964,478	1,957,641	1,852,324	1,846,955	1,845,283	1,957,641	1,845,283
Current period other comprehensive income (loss)	26	23	24	28	26	31	73	85
Ending Balance	1,993,254	1,971,762	1,964,478	1,876,237	1,852,324	1,846,955	1,993,254	1,876,237
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	146	123	99	(1,162)	(1,188)	(1,219)	99	(1,219)
Current period other comprehensive income (loss)	26	23	24	28	26	31
Ending Balance	172	$ 146	123	(1,134)	$ (1,162)	(1,188)	172	(1,134)
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)	99	(1,219)
Current period other comprehensive income (loss)							73	85
Ending Balance	$ 172			$ (1,134)			$ 172	$ (1,134)