Electric utility segment - Power purchase agreements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 140,000	$ 127,000
Hawaiian Electric Company
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	107,370	100,147
Hawaiian Electric Company | Kalaeloa Partners, L.P. (Kalaeloa)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	40,000	40,000
Hawaiian Electric Company | AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	37,000	29,000
Hawaiian Electric Company | HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	15,000	17,000
Hawaiian Electric Company | Puna Geothermal Venture
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	11,000	8,000
Hawaiian Electric Company | Hamakua Energy Partners, L.P. (HEP)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	7,000	7,000
Hawaiian Electric Company | Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 30,000	$ 26,000