Electric utility segment - Condensed consolidating statement of comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 42,512	$ 45,688	$ 46,054	$ 40,247	$ 88,200	$ 86,301
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		5,350		5,006	10,496
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,298)		(4,827)		(4,596)	(9,449)
Other comprehensive income (loss), net of taxes	13,699	9,241	(3,825)	(12,773)	22,940	(16,598)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	56,211		42,229		111,140	69,703
Consolidating adjustments
Condensed Statement of Income Captions [Line Items]
Net income for common stock	(8,086)	(11,849)	(9,080)	(9,325)	(19,935)	(18,405)
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)		(1,383)		(1,282)	(2,620)
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	640		1,382		1,280	2,619
Other comprehensive income (loss), net of taxes	(1)	(1)	(1)	0	(2)	(1)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	(8,087)		(9,081)		(19,937)	(18,406)
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	32,574	32,126	31,169	27,475	64,700	58,644
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	2,321		4,853		4,643	9,506
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,298)		(4,827)		(4,596)	(9,449)
Other comprehensive income (loss), net of taxes	23	24	26	31	47	57
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	32,597		31,195		64,747	58,701
HELCO | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	4,666	5,169	3,763	6,101	9,835	9,864
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		734		704	1,409
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(351)		(733)		(702)	(1,408)
Other comprehensive income (loss), net of taxes	1	1	1	0	2	1
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	4,667		3,764		9,837	9,865
Maui Electric | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	3,420	6,680	5,317	3,224	10,100	8,541
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		649		578	1,211
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(289)		(649)		(578)	(1,211)
Other comprehensive income (loss), net of taxes	0	0	0	0	0	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	3,420		5,317		10,100	8,541
Other subsidiaries | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	0	0	0	0	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		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	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	32,574	32,126	31,169	27,475	64,700	58,644
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	2,321		4,853		4,643	9,506
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,298)		(4,827)		(4,596)	(9,449)
Other comprehensive income (loss), net of taxes	23	$ 24	26	$ 31	47	57
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	$ 32,597		$ 31,195		$ 64,747	$ 58,701