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Electric utility segment - Rate proceedings (Details) - USD ($) $ in Thousands | Oct. 22, 2020 | May 13, 2020 | Nov. 13, 2019 | Apr. 18, 2018 | Sep. 30, 2020 | Dec. 31, 2019
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Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |
Regulatory assets |  |  |  |  | $ 677,683 | $ 715,080
Hawaiian Electric (parent only) |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |
Multi-year rate plan, term |  |  |  | 5 years |  |
Timeframe to acquire annual savings |  | 3 years |  |  |  |
Proposed annual savings |  | $ 25,000 |  |  |  |
Proposed annual savings, capital, percentage |  | 80.00% |  |  |  |
Proposed annual savings, operations and maintenance, percentage |  | 20.00% |  |  |  |
Hawaiian Electric (parent only) | Subsequent Event |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |
Effective interest rate of return | 7.37% |  |  |  |  |
Stipulated ROACE rate | 9.50% |  |  |  |  |
Period to file revised tariffs | 15 days |  |  |  |  |
Common equity capitalization rate | 58.00% |  |  |  |  |
HELCO |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |
Interim revenue requirement |  |  | $ 387,000 |  |  |
Rate base |  |  | $ 534,000 |  |  |
Effective interest rate of return |  |  | 7.52% |  |  |
Stipulated ROACE rate |  |  | 9.50% |  |  |
Common equity capitalization rate |  |  | 58.00% |  |  |
Amortization period for state investment tax credit |  |  | 10 years |  |  |
Risk sharing percentage, ratepayer |  |  | 98.00% |  |  |
Maximum exposure cap |  |  | $ 600 |  |  |
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |
Regulatory assets |  |  |  |  | $ 12,400 |

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