XML 78 R58.htm IDEA: XBRL DOCUMENT v3.20.4
Significant accounting policies - Additional Information (Detail)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
USD ($)
waterUtility
facility
Dec. 31, 2019
USD ($)
Significant Accounting Policies [Line Items]    
Number of electric generating facilities | facility 3  
Number of power generating facilities | facility 2  
Number of water pipeline projects | waterUtility 1  
Generating assets of Long Sault $ 13,223,906 $ 10,920,786
Long-term debt of Long Sault 7,234,541 6,182,415
Non-regulated energy sales 1,677,058 1,626,392
Interest expense on long-term debt and others 181,934 181,488
Long Sault and Saint-Damase Wind Powered Generating Facility | Primary Beneficiary | Power plant    
Significant Accounting Policies [Line Items]    
Generating assets of Long Sault 59,521 60,230
Long-term debt of Long Sault 20,328 21,754
Operating expenses and amortization 5,400 4,930
Interest expense on long-term debt and others $ 2,119 2,340
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 | Minimum    
Significant Accounting Policies [Line Items]    
Intangible asset, useful life 25 years  
Customer Relationships | Maximum    
Significant Accounting Policies [Line Items]    
Intangible asset, useful life 40 years  
Non-regulated energy sales    
Significant Accounting Policies [Line Items]    
Non-regulated energy sales $ 255,955 246,601
Non-regulated energy sales | Long Sault and Saint-Damase Wind Powered Generating Facility | Primary Beneficiary | Power plant    
Significant Accounting Policies [Line Items]    
Non-regulated energy sales $ 17,116 $ 17,108