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Share Capital - Summary of Dividends Declared and Recorded in the Consolidated Financial Statements (Detail) - CAD
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of Dividends [line items]    
Paid CAD 0 CAD 0
Dividends per share one [member]    
Disclosure of Dividends [line items]    
Dividend per Share CAD 0.1250  
Paid CAD 14,300,000  
Date Declared Feb. 22, 2017  
Record Date Mar. 31, 2017  
Payment Date Apr. 13, 2017  
Dividends per share two [member]    
Disclosure of Dividends [line items]    
Dividend per Share CAD 0.1250  
Paid CAD 14,200,000  
Date Declared May 10, 2017  
Record Date Jun. 30, 2017  
Payment Date Jul. 13, 2017  
Dividends per share three [member]    
Disclosure of Dividends [line items]    
Dividend per Share CAD 0.1250  
Paid CAD 14,200,000  
Date Declared Aug. 08, 2017  
Record Date Sep. 29, 2017  
Payment Date Oct. 12, 2017  
Dividends per share four [member]    
Disclosure of Dividends [line items]    
Dividend per Share CAD 0.1250  
Paid CAD 0  
Date Declared Nov. 08, 2017  
Record Date Dec. 31, 2017  
Payment Date Jan. 11, 2018