Electric utility segment - Condensed consolidating statement of changes in common stock equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Increase (decrease) in stockholders' equity
Beginning Balance	$ 2,097,386	$ 2,066,753
Net income for common stock	40,247	34,193
Other comprehensive income (loss), net of taxes	(12,773)	985
Common stock dividends	(33,741)	(33,713)
Ending Balance	2,091,777	2,065,588
Hawaiian Electric Company
Increase (decrease) in stockholders' equity
Beginning Balance	1,845,283	1,799,787
Net income for common stock	27,475	21,465
Other comprehensive income (loss), net of taxes	31	459
Common stock dividends	(25,826)	(21,942)
Common stock issuance expenses	(8)
Ending Balance	1,846,955	1,799,769
HELCO
Increase (decrease) in stockholders' equity
Beginning Balance	286,647	291,291
Net income for common stock	6,101	4,584
Other comprehensive income (loss), net of taxes	0	0
Common stock dividends	(3,821)	(3,874)
Common stock issuance expenses	0
Ending Balance	288,927	292,001
Maui Electric
Increase (decrease) in stockholders' equity
Beginning Balance	270,265	259,554
Net income for common stock	3,224	4,019
Other comprehensive income (loss), net of taxes	0	(1)
Common stock dividends	(3,006)	(2,986)
Common stock issuance expenses	0
Ending Balance	270,483	260,586
Other subsidiaries
Increase (decrease) in stockholders' equity
Beginning Balance	101	101
Net income for common stock	0	0
Other comprehensive income (loss), net of taxes	0	0
Common stock dividends	0	0
Common stock issuance expenses	0
Ending Balance	101	101
Consolidating adjustments
Increase (decrease) in stockholders' equity
Beginning Balance	(557,013)	(550,946)
Net income for common stock	(9,325)	(8,603)
Other comprehensive income (loss), net of taxes	0	1
Common stock dividends	6,827	6,860
Common stock issuance expenses	0
Ending Balance	(559,511)	(552,688)
Hawaiian Electric Company, Inc. and Subsidiaries
Increase (decrease) in stockholders' equity
Beginning Balance	1,845,283	1,799,787
Net income for common stock	27,475	21,465
Other comprehensive income (loss), net of taxes	31	459
Common stock dividends	(25,826)	(21,942)
Common stock issuance expenses	(8)
Ending Balance	$ 1,846,955	$ 1,799,769