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Long-Term Debt - Additional Information (Details)
$ in Millions, $ in Millions
 12 Months Ended
Jul. 19, 2019
CAD ($)
tranche
Dec. 31, 2020
CAD ($)
Dec. 31, 2019
CAD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2020
AUD ($)
Oct. 08, 2020
CAD ($)
Jan. 01, 2020
CAD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2019
AUD ($)
Disclosure of detailed information about borrowings [line items]                  
Number of tranches | tranche 2                
Additional revolving credit facilities amount $ 600,000,000.0                
Credit facility average interest rate   2.55% 3.77%            
Letter of credit outstanding   $ 8,800,000 $ 49,900,000            
Letter of credit issued and outstanding in addition   66,200,000 33,300,000            
Expire before 2022                  
Disclosure of detailed information about borrowings [line items]                  
Letter of credit issued and outstanding in addition   53,800,000 18,700,000            
Open-ended terms                  
Disclosure of detailed information about borrowings [line items]                  
Letter of credit issued and outstanding in addition   12,400,000 14,600,000            
Senior unsecured notes                  
Disclosure of detailed information about borrowings [line items]                  
Notional amount           $ 300,000,000.0      
Borrowings, interest rate           2.048%      
Revolving credit facility                  
Disclosure of detailed information about borrowings [line items]                  
Revolving credit facilities amount   800,000,000.0     $ 800.0        
Amount available under the facility   786,500,000 282,600,000            
Notes payable                  
Disclosure of detailed information about borrowings [line items]                  
Aggregate maturity value of notes   69,800,000 90,700,000            
Notes payable | US funds                  
Disclosure of detailed information about borrowings [line items]                  
Carrying amount of notes payable   5,700,000 4,200,000 $ 4.5       $ 3.2  
Notes payable | Foreign currencies                  
Disclosure of detailed information about borrowings [line items]                  
Carrying amount of notes payable   17,200,000 23,200,000            
Notes payable | Australian funds                  
Disclosure of detailed information about borrowings [line items]                  
Carrying amount of notes payable   $ 38,400,000 $ 52,000,000.0   $ 39.2       $ 57.1
Notes payable | Weighted average                  
Disclosure of detailed information about borrowings [line items]                  
Borrowings, interest rate   2.40% 2.70% 2.40% 2.40%     2.70% 2.70%
Term loan                  
Disclosure of detailed information about borrowings [line items]                  
Revolving credit facilities amount   $ 310,000,000.0              
Term Loan Tranche A | Canadian funds                  
Disclosure of detailed information about borrowings [line items]                  
Revolving credit facility payable   150,000,000.0 $ 150,000,000.0            
Term Loan Tranche B | Canadian funds                  
Disclosure of detailed information about borrowings [line items]                  
Revolving credit facility payable   160,000,000.0 160,000,000.0            
Letter of credit                  
Disclosure of detailed information about borrowings [line items]                  
Revolving credit facilities amount             $ 100,000,000.0    
Surety facilities                  
Disclosure of detailed information about borrowings [line items]                  
Bonds issued under surety facilities   155,100,000 380,600,000 $ 121.8       $ 293.0  
Surety facilities expiring before September 2026                  
Disclosure of detailed information about borrowings [line items]                  
Bonds issued under surety facilities   $ 12,000,000.0 $ 11,500,000