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Electric utility segment - Rate proceedings (Details) - USD ($)
$ in Thousands
May 13, 2020
Nov. 13, 2019
Jun. 30, 2020
Dec. 31, 2019
Regulatory Projects and Legal Obligations [Line Items]        
Regulatory assets     $ 682,570 $ 715,080
Hawaiian Electric (parent only)        
Regulatory Projects and Legal Obligations [Line Items]        
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%      
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    
Proposed final tariffs and revised tariff period   30 days    
Hawaiian Electric Company, Inc. and Subsidiaries        
Regulatory Projects and Legal Obligations [Line Items]        
Regulatory assets     $ 6,500