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Equity - Summary of Class A Common Shares and Class B Subordinate Voting Shares Issued and Outstanding (Detail)
 12 Months Ended
Dec. 31, 2017
shares
Dec. 31, 2016
shares
Disclosure of classes of share capital [line items]    
Options exercised 2,275,000 647,000
Class A Common Shares [member]    
Disclosure of classes of share capital [line items]    
Beginning balance 9,353,000 9,353,000
Class A share conversion (1,576,166)  
Ending balance 7,777,000 9,353,000
Class B Subordinate Voting Shares [member]    
Disclosure of classes of share capital [line items]    
Beginning balance 567,546,000 566,899,000
Class A share conversion 1,576,166  
Options exercised 2,275,000 647,000
Acquired and cancelled pursuant to normal course issuer bid (h) (5,891,000)  
Ending balance 565,506,000 567,546,000