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Income Taxes - Additional Information (Detail) - CAD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure Of Temporary Difference Unused Tax Losses And Unused Tax Credits [Line Items]        
US federal corporate tax rate   35.00%    
Deferred income tax expense on revaluation of US federal income tax rate   $ 15,800,000    
Long-term receivable for alternative minimum tax carryforward balance   2,300,000    
Loss carryforwards not recognized as deferred incom tax asset   31,500    
Unrecognized tax benefits   1,980,000 $ 1,923,000 $ 19,618,000
Interest and penalties included in unrecognized tax benefits   500,000 400,000  
Unrecognized tax benefits realized in next twelve months   0 0  
Temporary differences [Member]        
Disclosure Of Temporary Difference Unused Tax Losses And Unused Tax Credits [Line Items]        
Tax effected temporary differences related to US operations   $ 38,800,000 $ 14,000,000  
Scenario, Forecast [Member]        
Disclosure Of Temporary Difference Unused Tax Losses And Unused Tax Credits [Line Items]        
US federal corporate tax rate 21.00%