Electric utility segment - Commitments and contingencies (Details) private_photovoltaic_system in Thousands					1 Months Ended												6 Months Ended	11 Months Ended	12 Months Ended	22 Months Ended
	Apr. 30, 2017 USD ($)	Apr. 27, 2017 USD ($)	Aug. 11, 2016 USD ($)	Jan. 05, 2016 USD ($)	Jun. 30, 2017 USD ($) private_photovoltaic_system $ / kWh	Oct. 31, 2016 customer	Jul. 31, 2016 MW	Apr. 30, 2016 island private_photovoltaic_system	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 MW	Apr. 30, 2014 order	Aug. 31, 2012 MW	May 31, 2012 MW	Oct. 31, 1988 MW	Mar. 31, 1988 MW	Jun. 30, 2017 USD ($) private_photovoltaic_system MW	Jun. 30, 2017 USD ($) private_photovoltaic_system	Jun. 30, 2017 USD ($) private_photovoltaic_system	Jun. 30, 2017 USD ($) private_photovoltaic_system	Dec. 31, 2016 USD ($)	Jul. 31, 2014 USD ($)
Regulatory projects and legal obligations
Purchase commitment, period (in years)																30 years
Minimum power volume required (in megawatts) | MW													186			180
Additional capacity requirement (in megawatts) | MW											9
ERP/EAM Project, expected costs																						$ 82,400,000
ERP/EAM cost recovery cap			$ 77,600,000
Public utility, ERP/EAM required pass through savings to customers			$ 244,000,000
ERP/EAM project service period (in years)			12 years
AFUDC rate (as a percent)		1.75%
ERP/EAM implementation project costs																		$ 14,000,000
ERP/EAM implementation project, operations and management																		2,500,000
ERP/EAM implementation project, capital costs																		1,100,000
ERP/EAM implementation project, deferred costs																		10,400,000
Schofield generating station facility capacity (in megawatts) | MW													50
Schofield generating station project, budgetary cap				$ 157,300,000						$ 167,000,000
Percent of costs recoverable through recovery mechanisms other than base rates (as a percent)										90.00%
Decrease in project costs				$ 9,700,000
Project lease term (in years)				35 years
Project cost incurred																				$ 87,800,000
West Lock PV Project, energy generated (in megawatts) | MW							20
West Lock PV Project, cost cap					$ 67,000,000												$ 67,000,000	67,000,000	$ 67,000,000	67,000,000
West Lock PV Project, maximum energy cost (in dollars per kilowatt hours) | $ / kWh					0.0956
West Lock PV Project, project costs incurred																			400,000
Accounts receivable and unbilled revenues, net					$ 249,539,000												$ 249,539,000	$ 249,539,000	$ 249,539,000	$ 249,539,000	$ 237,950,000
Environmental regulation
Number of orders from regulatory agency (in orders) | order												4
Percent of energy production from renewable energy sources (as a percent)								100.00%
Renewable energy plan term (in years)								5 years
Renewable energy plan, number of islands served | island								5
Number of private systems estimated to be needed to meet environmental goals | private_photovoltaic_system								165
Number of private systems, current | private_photovoltaic_system					79												79	79	79	79
Public utilities, duration of Time of Use Program (in years)						2 years
Public utilities, number of customers impacted by Time Of Use Program (in customers) | customer						5,000
Decoupling order, service reliability performance, historical measurement period (in years)	10 years
Maximum penalty as a percent of equity (as a percent)	0.20%
Service reliability, maximum penalty	$ 3,000,000
Dead band percentage above or below the target (as a percent)	3.00%
Maximum incentive, percent of return on equity (as a percent)	0.08%
Call center performance, maximum penalty	$ 1,200,000
Threshold of capital expenditures in excess of customer contributions for qualification for major project interim recovery		$ 2,500,000.0
PCB Contamination
Environmental regulation
Valuation allowances and reserves					$ 4,900,000												$ 4,900,000	$ 4,900,000	$ 4,900,000	$ 4,900,000
Hawaii Electric Light Company, Inc. (HELCO) | Hamakua Energy Partners, L.P. (HEP)
Regulatory projects and legal obligations
Potential purchase price									$ 84,500,000
Hawaii Electric Light Company, Inc. (HELCO) | Maximum
Regulatory projects and legal obligations
Power purchase capacity that Increases from initial capacity (in megawatts) | MW																	60
Hamakua Energy Partners, L.P. (HEP)
Regulatory projects and legal obligations
Percent of island's generating capacity (as a percent)																	23.00%
Maui Electric
Environmental regulation
Additional accrued investigation and estimated cleanup costs					3,500,000												$ 3,500,000	3,500,000	3,500,000	3,500,000
Hu Honua Bioenergy, LLC
Regulatory projects and legal obligations
Minimum power volume required (in megawatts) | MW														21.5
Hawaiian Telcom
Regulatory projects and legal obligations
Accounts receivable and unbilled revenues, net					22,100,000												22,100,000	22,100,000	22,100,000	22,100,000
Reserve for interest accrued					4,900,000												4,900,000	4,900,000	4,900,000	4,900,000
Hawaiian Telcom | Hawaii Electric Light Company, Inc. (HELCO)
Regulatory projects and legal obligations
Accounts receivable and unbilled revenues, net					6,000,000												6,000,000	6,000,000	6,000,000	6,000,000
Hawaiian Telcom | Hawaiian Electric Company
Regulatory projects and legal obligations
Accounts receivable and unbilled revenues, net					14,800,000												14,800,000	14,800,000	14,800,000	14,800,000
Hawaiian Telcom | Maui Electric
Regulatory projects and legal obligations
Accounts receivable and unbilled revenues, net					$ 1,300,000												$ 1,300,000	$ 1,300,000	$ 1,300,000	$ 1,300,000
Kalaeloa Partners, L.P. (Kalaeloa) | Hawaiian Electric Company
Regulatory projects and legal obligations
Power purchase capacity that Increases from initial capacity (in megawatts) | MW															180