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Concentrations of credit risk - Additional Information (Detail) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended
Oct. 31, 2015
Jan. 31, 2016
Jan. 31, 2015
Concentration Risk [Line Items]      
Cash, FDIC insured amount   $ 4.9  
Sales Revenue, Goods, Net      
Concentration Risk [Line Items]      
Concentration risk, percentage     17.00%
Sales Revenue, Goods, Net | Customer One [Member]      
Concentration Risk [Line Items]      
Concentration risk, percentage   14.00%  
Sales Revenue, Goods, Net | Customer Two [Member]      
Concentration Risk [Line Items]      
Concentration risk, percentage   13.00%  
Accounts Receivable      
Concentration Risk [Line Items]      
Concentration risk, percentage 19.00%    
Accounts Receivable | Customer One [Member]      
Concentration Risk [Line Items]      
Concentration risk, percentage   17.00%  
Accounts Receivable | Customer Two [Member]      
Concentration Risk [Line Items]      
Concentration risk, percentage   15.00%