Electric utility segment - Condensed consolidating statement of comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 40,247	$ 34,193
Derivatives qualifying as cash flow hedges:
Reclassification adjustment to net income, net of tax benefits	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 of $___, $2,160, $___ and $4,221, respectively	5,146	3,921
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(4,622)	(3,613)
Other comprehensive income (loss), net of taxes	(12,773)	985
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	27,474	35,178
Hawaiian Electric Company
Condensed Statement of Income Captions [Line Items]
Net income for common stock	27,475	21,465
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 of $___, $2,160, $___ and $4,221, respectively	4,653	3,618
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(4,622)	(3,613)
Other comprehensive income (loss), net of taxes	31	459
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	27,506	21,924
HELCO
Condensed Statement of Income Captions [Line Items]
Net income for common stock	6,101	4,584
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 of $___, $2,160, $___ and $4,221, respectively	675	503
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(675)	(503)
Other comprehensive income (loss), net of taxes	0	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	6,101	4,584
Maui Electric
Condensed Statement of Income Captions [Line Items]
Net income for common stock	3,224	4,019
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 of $___, $2,160, $___ and $4,221, respectively	562	466
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(562)	(467)
Other comprehensive income (loss), net of taxes	0	(1)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	3,224	4,018
Other subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income for common stock	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 of $___, $2,160, $___ and $4,221, respectively	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
Consolidating adjustments
Condensed Statement of Income Captions [Line Items]
Net income for common stock	(9,325)	(8,603)
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 of $___, $2,160, $___ and $4,221, respectively	(1,237)	(969)
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	1,237	970
Other comprehensive income (loss), net of taxes	0	1
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	(9,325)	(8,602)
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income for common stock	27,475	21,465
Derivatives qualifying as cash flow hedges:
Reclassification adjustment to net income, net of tax benefits	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 of $___, $2,160, $___ and $4,221, respectively	4,653	3,618
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(4,622)	(3,613)
Other comprehensive income (loss), net of taxes	31	459
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	$ 27,506	$ 21,924