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Income Taxes - Summary of Reconciliation of Unrecognized Tax Benefits (Detail) - CAD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Reconciliation Of Changes In Deferred Tax Liability Asset [Abstract]    
Unrecognized tax benefits, beginning of year $ 1,923 $ 19,618
Additions:    
Prior year’s tax positions 57 56
Reductions:    
Prior year’s tax positions   (17,751)
Unrecognized tax benefits, end of year $ 1,980 $ 1,923