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Financial Instruments - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2017
CAD
Dec. 31, 2016
CAD
May 06, 2016
CAD
Disclosure of detailed information about financial instruments [line items]      
Maximum amount of credit risk exposure CAD 1,252,600,000 CAD 1,203,500,000  
Number of target days of revenue in trade receivables 55 days 57 days  
Amount of revolving credit facility     CAD 1,250,000,000
0.5% Increase in interest rates [member]      
Disclosure of detailed information about financial instruments [line items]      
Impact on net income CAD 2,500,000    
0.5% Decrease in interest rates [member]      
Disclosure of detailed information about financial instruments [line items]      
Impact on net income 2,500,000    
1.0% Increase in equity price risk [member]      
Disclosure of detailed information about financial instruments [line items]      
Equity price impact on comprehensive income 400,000    
1.0% Decrease in equity Price risk [member]      
Disclosure of detailed information about financial instruments [line items]      
Equity price impact on comprehensive income CAD 400,000    
Top of range [member]      
Disclosure of detailed information about financial instruments [line items]      
Net debt to EBITDA ratio 2.5    
Top of range [member] | One point zero percentage decrease in exchange rates [member]      
Disclosure of detailed information about financial instruments [line items]      
Impact on net income CAD 200,000    
Top of range [member] | One point zero percentage increase in exchange rates [member]      
Disclosure of detailed information about financial instruments [line items]      
Impact on net income 200,000    
Revolving credit facilities [member]      
Disclosure of detailed information about financial instruments [line items]      
Amount of revolving credit facility 800,000,000   CAD 800,000,000
Unused capacity amount CAD 538,300,000 CAD 329,200,000