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Provisions - Additional Information (Detail)
CAD in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2017
CAD
Dec. 31, 2017
USD ($)
Dec. 31, 2016
CAD
Disclosure of Provisions [line items]      
Long-term portion CAD 81.7   CAD 80.7
Anticipated lease exit liability to be recorded in fourth quarter of 2018 | $   $ 15.0  
Self-insured liabilities provision [member]      
Disclosure of Provisions [line items]      
Long-term portion CAD 65.9   CAD 64.0
Bottom of range [member]      
Disclosure of Provisions [line items]      
Cash outflows for existing provisions expected period 1 year    
Top of range [member]      
Disclosure of Provisions [line items]      
Cash outflows for existing provisions expected period 5 years