Bank segment - Comprehensive income data (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
Net unrealized gains (losses) on available-for-sale investment securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of (taxes) benefits of $(3,455) and $4,867, respectively	9,439	(13,297)
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of (taxes) benefits of $(1,166) and $694, respectively	2,503	5,146
Other comprehensive income (loss), net of taxes	9,241	(12,773)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	54,929	27,474
Net unrealized gains (losses) on securities arising during the period, (taxes) benefits	(3,455)	4,867
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, taxes (benefits)	870	1,792
American Savings Bank (ASB)
Condensed Statement of Income Captions [Line Items]
Net income for common stock	20,839	18,960
Net unrealized gains (losses) on available-for-sale investment securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of (taxes) benefits of $(3,455) and $4,867, respectively	9,439	(13,297)
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of (taxes) benefits of $(1,166) and $694, respectively	(3,187)	1,222
Other comprehensive income (loss), net of taxes	6,252	(12,075)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	27,091	6,885
Net unrealized gains (losses) on securities arising during the period, (taxes) benefits	(3,455)	4,867
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, taxes (benefits)	$ (1,166)	$ 694