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Regulatory Matters - Regulatory Assets and Liabilities - Footnote (Details)
$ in Thousands
 1 Months Ended 3 Months Ended 12 Months Ended
Aug. 01, 2023
USD ($)
Feb. 28, 2021
USD ($)
Sep. 30, 2023
USD ($)
Dec. 31, 2023
USD ($)
Jan. 30, 2024
USD ($)
Dec. 31, 2022
USD ($)
Mar. 01, 2020
MWac
Regulatory Liabilities [Line Items]              
Regulatory asset, amortization period       26 years      
Regulatory assets       $ 1,327,683   $ 1,271,501  
Capital expenditure shortfall refundable to customers (percent)       80.00%      
Retroactive rate adjustment collection period       24 months      
Regulatory liability, disallowed securitization costs       $ 63,495      
Empire Electric              
Regulatory Liabilities [Line Items]              
Public utilities, incurred cost one-time net gain (loss)   $ 63,495 $ 48,452        
Minimum | Rate adjustment mechanism              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period       1 year      
Maximum | Rate adjustment mechanism              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period       5 years      
Fuel and commodity cost adjustments              
Regulatory Liabilities [Line Items]              
Asset retirement obligation           21,283  
Regulatory assets       $ 326,418   388,294  
Fuel and commodity cost adjustments | Minimum              
Regulatory Liabilities [Line Items]              
Regulatory asset, amortization period       6 months      
Fuel and commodity cost adjustments | Maximum              
Regulatory Liabilities [Line Items]              
Regulatory asset, amortization period       24 months      
Retired generating plant              
Regulatory Liabilities [Line Items]              
Regulatory assets       $ 183,732   174,609  
Coal generation capacity (MW) | MWac             200
Deferred capitalized costs              
Regulatory Liabilities [Line Items]              
Regulatory asset, amortization period       20 years      
Regulatory assets       $ 124,517   90,121  
Capitalized operating and maintenance costs, recovery rate, (percent)       2.43%      
Pension and post-employment benefits              
Regulatory Liabilities [Line Items]              
Regulatory assets       $ 68,822   80,736  
Future service years of employees       10 years      
Pension and post-employment benefits | Minimum              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period       3 years      
Pension and post-employment benefits | Maximum              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period       8 years      
Environmental costs              
Regulatory Liabilities [Line Items]              
Regulatory assets       $ 66,779   70,529  
Environmental remediation, rate recovery period       7 years      
Wildfire mitigation and vegetation management              
Regulatory Liabilities [Line Items]              
Regulatory assets       $ 64,146   66,156  
Regulatory assets, recovery period       2 years      
Clean energy and other customer programs              
Regulatory Liabilities [Line Items]              
Regulatory assets       $ 37,214   28,145  
Clean energy and other customer programs | Minimum              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period       6 years      
Clean energy and other customer programs | Maximum              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period       10 years      
Rate review costs              
Regulatory Liabilities [Line Items]              
Regulatory assets       $ 8,815   9,481  
Rate review costs | Minimum              
Regulatory Liabilities [Line Items]              
Costs capitalized and amortized period       1 year      
Rate review costs | Maximum              
Regulatory Liabilities [Line Items]              
Costs capitalized and amortized period       5 years      
Long-term maintenance contract              
Regulatory Liabilities [Line Items]              
Regulatory assets       $ 4,932   6,504  
Regulatory assets, recovery period       5 years      
Midwest Extreme Weather Event | Fuel and commodity cost adjustments              
Regulatory Liabilities [Line Items]              
Issuance of securitized tariff bonds, authorized amount           221,646  
Public utilities, incurred cost one-time net gain (loss) $ 63,495            
Public utilities, incurred cost one-time net gain (loss), net of tax     $ 48,452        
Energy Transistion Costs | Fuel and commodity cost adjustments              
Regulatory Liabilities [Line Items]              
Issuance of securitized tariff bonds, authorized amount           $ 140,774  
Securitized Utility Tariff Bonds due January 1, 2035 | Fuel and commodity cost adjustments | Subsequent Event              
Regulatory Liabilities [Line Items]              
Regulatory assets         $ 180,500    
Percentage of public utilities, issuance of securitized tariff bonds         0.04943    
Securitized Utility Tariff Bonds due January 1, 2039 | Fuel and commodity cost adjustments | Subsequent Event              
Regulatory Liabilities [Line Items]              
Regulatory assets         $ 125,000    
Percentage of public utilities, issuance of securitized tariff bonds         0.05091