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Significant accounting policies - Additional Information (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
USD ($)
facility
Dec. 31, 2023
USD ($)
Significant Accounting Policies [Line Items]    
Number of electric generating facilities | facility 3  
Cost of plant in service $ 560,729 $ 552,701
Accumulated depreciation related to commonly owned facilities 103,319 83,283
Expenditures $ 69,637 72,584
Number of power generating facilities | facility 1  
Generating assets of Long Sault $ 16,961,757 18,373,961
Non-regulated energy sales 2,319,538 2,403,924
Interest expense on long-term debt and others 363,576 308,440
Non-Regulated Energy    
Significant Accounting Policies [Line Items]    
Non-regulated energy sales 35,328 34,322
Long Sault and Saint-Damase Wind Powered Generating Facility | Primary Beneficiary | Power plant    
Significant Accounting Policies [Line Items]    
Generating assets of Long Sault 28,832 29,537
Long-term debt of Long Sault 9,212 12,738
Operating expenses and amortization 3,180 3,053
Interest expense on long-term debt and others 1,066 1,384
Long Sault and Saint-Damase Wind Powered Generating Facility | Primary Beneficiary | Power plant | Non-Regulated Energy    
Significant Accounting Policies [Line Items]    
Non-regulated energy sales $ 11,453 $ 11,732
Minimum    
Significant Accounting Policies [Line Items]    
Ownership interest in commonly owned facilities 7.52%  
Lease renewal term 1 year  
Maximum    
Significant Accounting Policies [Line Items]    
Ownership interest in commonly owned facilities 60.00%  
Lease renewal term 5 years  
Power sales contracts | Minimum    
Significant Accounting Policies [Line Items]    
Intangible asset, useful life 6 years  
Power sales contracts | Maximum    
Significant Accounting Policies [Line Items]    
Intangible asset, useful life 25 years  
Interconnection agreements    
Significant Accounting Policies [Line Items]    
Intangible asset, useful life 40 years  
Customer relationships (a) | Minimum    
Significant Accounting Policies [Line Items]    
Intangible asset, useful life 25 years  
Customer relationships (a) | Maximum    
Significant Accounting Policies [Line Items]    
Intangible asset, useful life 40 years