Electric utility segment - Condensed consolidating statement of comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 45,688	$ 40,247
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	2,503	5,146
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,298)	(4,622)
Other comprehensive income (loss), net of taxes	9,241	(12,773)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	54,929	27,474
Consolidating adjustments
Condensed Statement of Income Captions [Line Items]
Net income for common stock	(11,849)	(9,325)
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	(641)	(1,237)
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	640	1,237
Other comprehensive income (loss), net of taxes	(1)	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	(11,850)	(9,325)
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	32,126	27,475
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	2,322	4,653
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,298)	(4,622)
Other comprehensive income (loss), net of taxes	24	31
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	32,150	27,506
HELCO | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	5,169	6,101
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	352	675
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(351)	(675)
Other comprehensive income (loss), net of taxes	1	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	5,170	6,101
Maui Electric | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	6,680	3,224
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	289	562
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(289)	(562)
Other comprehensive income (loss), net of taxes	0	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	6,680	3,224
Other subsidiaries | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	0	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
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	0	0
Other comprehensive income (loss), net of taxes	0	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	0	0
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income for common stock	32,126	27,475
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	2,322	4,653
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,298)	(4,622)
Other comprehensive income (loss), net of taxes	24	31
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	$ 32,150	$ 27,506