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Income taxes - Additional Information (Detail)
12 Months Ended
Mar. 31, 2018
USD ($)
Mar. 31, 2018
CAD ($)
Mar. 25, 2017
USD ($)
Mar. 26, 2016
USD ($)
Tax Credit Carryforward [Line Items]        
Accrued interest or penalties related to uncertain tax positions $ 0      
Non cash valuation allowance 10,002,000   $ 8,781,000  
Current tax payable $ 0   $ 0 $ 0
Earliest Tax Year [Member]        
Tax Credit Carryforward [Line Items]        
Open tax year 2011      
Latest Tax Year [Member]        
Tax Credit Carryforward [Line Items]        
Open tax year 2018      
Domestic Tax Authority [Member]        
Tax Credit Carryforward [Line Items]        
Federal non capital losses $ 27,300,000 $ 35,200,000    
Domestic Tax Authority [Member] | Investment Tax Credit Carryforward [Member]        
Tax Credit Carryforward [Line Items]        
Capital losses $ 202,000 260,000    
Expire date Between 2023 and 2038.      
Domestic Tax Authority [Member] | Capital Loss Carryforward [Member]        
Tax Credit Carryforward [Line Items]        
Capital losses $ 100,000 $ 200,000