Electric utility segment - Power purchase agreements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 161,000	$ 158,000	$ 441,000	$ 413,000
Hawaiian Electric Company
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	123,893	118,751	340,498	313,730
Hawaiian Electric Company | Kalaeloa Partners, L.P. (Kalaeloa)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	48,000	44,000	136,000	109,000
Hawaiian Electric Company | AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	39,000	38,000	103,000	112,000
Hawaiian Electric Company | HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	18,000	19,000	51,000	52,000
Hawaiian Electric Company | Puna Geothermal Venture
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	10,000	7,000	28,000	19,000
Hawaiian Electric Company | Hamakua Energy Partners, L.P. (HEP)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	8,000	8,000	25,000	23,000
Hawaiian Electric Company | Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 38,000	$ 42,000	$ 98,000	$ 98,000