Bank segment - Comprehensive income data (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
Net unrealized gains (losses) on securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of (taxes) benefits of $4,867 and $(148), respectively	(13,297)	223
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 $694 and $404, respectively	5,146	3,921
Other comprehensive income (loss), net of taxes	(12,773)	985
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	27,474	35,178
Net unrealized gains (losses) on securities arising during the period, taxes (benefits)	(4,867)	148
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, taxes (benefits)	(1,792)	(2,502)
American Savings Bank (ASB)
Condensed Statement of Income Captions [Line Items]
Net income for common stock	18,960	15,813
Net unrealized gains (losses) on securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of (taxes) benefits of $4,867 and $(148), respectively	(13,297)	223
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 $694 and $404, respectively	1,222	612
Other comprehensive income (loss), net of taxes	(12,075)	835
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	6,885	16,648
Net unrealized gains (losses) on securities arising during the period, taxes (benefits)	(4,867)	148
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, taxes (benefits)	$ (694)	$ (404)