Electric utility segment - Condensed consolidating statement of comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 65,900	$ 60,073	$ 152,201	$ 132,927
Derivatives qualifying as cash flow hedges:
Reclassification adjustment to net income, net of tax benefits	0	0	0	454
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	5,259	3,942	15,755	11,793
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(4,725)	(3,596)	(14,174)	(10,790)
Other comprehensive income (loss), net of taxes	(4,589)	554	(21,187)	3,909
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	61,311	60,627	131,014	136,836
Consolidating adjustments
Condensed Statement of Income Captions [Line Items]
Net income for common stock	(16,636)	(12,767)	(35,041)	(29,306)
Derivatives qualifying as cash flow hedges:
Reclassification adjustment to net income, net of tax benefits				0
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	(1,311)	(880)	(3,931)	(2,642)
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	1,311	880	3,930	2,641
Other comprehensive income (loss), net of taxes	0	0	(1)	(1)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	(16,636)	(12,767)	(35,042)	(29,307)
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	49,712	47,487	108,356	94,596
Derivatives qualifying as cash flow hedges:
Reclassification adjustment to net income, net of tax benefits				454
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	4,753	3,618	14,259	10,857
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(4,725)	(3,596)	(14,174)	(10,790)
Other comprehensive income (loss), net of taxes	28	22	85	521
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	49,740	47,509	108,441	95,117
HELCO | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	9,175	6,434	19,039	14,650
Derivatives qualifying as cash flow hedges:
Reclassification adjustment to net income, net of tax benefits				0
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	705	476	2,114	1,428
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(705)	(476)	(2,113)	(1,427)
Other comprehensive income (loss), net of taxes	0	0	1	1
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	9,175	6,434	19,040	14,651
Maui Electric | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	7,461	6,333	16,002	14,656
Derivatives qualifying as cash flow hedges:
Reclassification adjustment to net income, net of tax benefits				0
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	606	404	1,817	1,214
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(606)	(404)	(1,817)	(1,214)
Other comprehensive income (loss), net of taxes	0	0	0	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	7,461	6,333	16,002	14,656
Other subsidiaries | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	0	0	0	0
Derivatives qualifying as cash flow hedges:
Reclassification adjustment to net income, net of tax benefits				0
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	0	0	0	0
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	0	0	0	0
Other comprehensive income (loss), net of taxes	0	0	0	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	0	0	0	0
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income for common stock	49,712	47,487	108,356	94,596
Derivatives qualifying as cash flow hedges:
Reclassification adjustment to net income, net of tax benefits	0	0	0	454
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	4,753	3,618	14,259	10,857
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(4,725)	(3,596)	(14,174)	(10,790)
Other comprehensive income (loss), net of taxes	28	22	85	521
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	$ 49,740	$ 47,509	$ 108,441	$ 95,117