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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 |  |  |  |  |  |  |

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