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Income taxes - Additional Information (Detail)
 12 Months Ended
Mar. 25, 2017
USD ($)
Mar. 25, 2017
CAD
Mar. 26, 2016
USD ($)
Mar. 28, 2015
USD ($)
Tax Credit Carryforward [Line Items]        
Accrued interest or penalties related to uncertain tax positions $ 0      
Non cash valuation allowance 53,311,000   $ 57,285,000  
Reversal of valuation allowance 5,300,000      
Deferred income taxes 5,303,000      
Current tax receivable $ (140,000)      
Current tax payable     $ 35,000 $ 0
Minimum [Member]        
Tax Credit Carryforward [Line Items]        
Deferred tax assets realized period 1 year      
Maximum [Member]        
Tax Credit Carryforward [Line Items]        
Deferred tax assets realized period 3 years      
Alternative Minimum Tax Credit [Member]        
Tax Credit Carryforward [Line Items]        
Investment tax credits $ 1,100,000      
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 2017      
Domestic Tax Authority [Member]        
Tax Credit Carryforward [Line Items]        
Federal non capital losses $ 18,300,000 CAD 24,500,000    
Domestic Tax Authority [Member] | Investment Tax Credit Carryforward [Member]        
Tax Credit Carryforward [Line Items]        
Investment tax credits $ 194,000 CAD 260,000    
Expire date Between 2023 and 2036.      
Foreign Tax Authority [Member]        
Tax Credit Carryforward [Line Items]        
Federal non capital losses $ 106,000,000      
Federal net operating loss carry forwards expiration Dates Beginning in fiscal 2020 through fiscal 2034      
State and Local Jurisdiction [Member]        
Tax Credit Carryforward [Line Items]        
Federal non capital losses $ 92,200,000      
Federal net operating loss carry forwards expiration Dates Beginning in fiscal 2018 through fiscal 2034      
Foreign Country Section Three Eight Two Limitation [Member]        
Tax Credit Carryforward [Line Items]        
Pre-acquisition net operating loss $ 35,300,000      
Pre-acquisition net operating loss limited $ 953,000