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Share Capital - Share-based Payment Transactions - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2018
CAD ($)
yr
shares
Dec. 31, 2017
CAD ($)
yr
shares
Dec. 31, 2016
Disclosure of range of exercise prices of outstanding share options [line items]      
Fair value of options granted The fair value of options granted is determined at the date of grant using the Black-Scholes option-pricing model.    
Number of share subject to options, Granted 1,112,779 1,229,689  
Estimated fair value of options granted on the grant date $ 5.73 $ 5.03  
Expected hold period to exercise (years) | yr 3.50 3.50  
Options remained unvested compensation cost $ 5,200,000 $ 4,800,000  
Options remained unvested weighted average period | yr 1.06 1.06  
Performance share units (PSUs) [member]      
Disclosure of range of exercise prices of outstanding share options [line items]      
Number of shares issued 280,884 284,777  
Number of equity instruments forfeited 29,668 19,617  
Number of shares outstanding 744,081 686,250  
Outstanding fair value $ 6,000,000 $ 14,300,000  
Number of shares paid | shares 193,385    
Paid at fair value $ 3,200,000    
Performance share units (PSUs) [member] | Bottom of range [member]      
Disclosure of range of exercise prices of outstanding share options [line items]      
Number of units vest percentage 0.00%    
Performance share units (PSUs) [member] | Top of range [member]      
Disclosure of range of exercise prices of outstanding share options [line items]      
Number of units vest percentage 200.00%    
Deferred share unit [member]      
Disclosure of range of exercise prices of outstanding share options [line items]      
Number of shares issued 46,356 38,625  
Number of shares outstanding 306,459 438,969  
Outstanding fair value $ 9,000,000 $ 15,500,000  
Number of shares paid | shares 178,866 66,021  
Paid at fair value $ 6,200,000 $ 2,100,000  
Estimated historical data [member]      
Disclosure of range of exercise prices of outstanding share options [line items]      
Expected hold period to exercise (years) | yr 5    
Officers and employees [member]      
Disclosure of range of exercise prices of outstanding share options [line items]      
Number of share subject to options, Granted 4,987,542 4,426,237 3,655,020
Number of share subject to options, Granted 1,112,779 1,229,689  
Officers and employees [member] | Bottom of range [member]      
Disclosure of range of exercise prices of outstanding share options [line items]      
Share option price per share $ 14.88    
Officers and employees [member] | Top of range [member]      
Disclosure of range of exercise prices of outstanding share options [line items]      
Share option price per share $ 32.98