Electric utility segment - Condensed consolidating statement of changes in common stock equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Increase (decrease) in stockholders' equity
Beginning Balance	$ 2,162,280	$ 2,097,386
Net income for common stock	45,688	40,247
Other comprehensive income (loss), net of taxes	9,241	(12,773)
Common stock dividends	(34,860)	(33,741)
Ending Balance	2,183,515	2,091,777
Consolidating adjustments
Increase (decrease) in stockholders' equity
Beginning Balance	(576,838)	(557,013)
Net income for common stock	(11,849)	(9,325)
Other comprehensive income (loss), net of taxes	(1)	0
Common stock dividends	6,312	6,827
Common stock issuance expenses	2	0
Ending Balance	(582,374)	(559,511)
Hawaiian Electric (parent only) | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance	1,957,641	1,845,283
Net income for common stock	32,126	27,475
Other comprehensive income (loss), net of taxes	24	31
Common stock dividends	(25,313)	(25,826)
Common stock issuance expenses	0	(8)
Ending Balance	1,964,478	1,846,955
HELCO | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance	295,874	286,647
Net income for common stock	5,169	6,101
Other comprehensive income (loss), net of taxes	1	0
Common stock dividends	(2,545)	(3,821)
Common stock issuance expenses	(2)	0
Ending Balance	298,497	288,927
Maui Electric | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance	280,863	270,265
Net income for common stock	6,680	3,224
Other comprehensive income (loss), net of taxes	0	0
Common stock dividends	(3,767)	(3,006)
Common stock issuance expenses	0	0
Ending Balance	283,776	270,483
Other subsidiaries | Reportable Legal Entities
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	0
Ending Balance	101	101
Hawaiian Electric Company, Inc. and Subsidiaries
Increase (decrease) in stockholders' equity
Beginning Balance	1,957,641	1,845,283
Net income for common stock	32,126	27,475
Other comprehensive income (loss), net of taxes	24	31
Common stock dividends	(25,313)	(25,826)
Common stock issuance expenses	0	(8)
Ending Balance	$ 1,964,478	$ 1,846,955