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Concentrations of credit risk - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Apr. 30, 2017
Apr. 30, 2016
Apr. 30, 2017
Apr. 30, 2016
Oct. 31, 2016
Concentration Risk [Line Items]          
Cash, FDIC insured amount $ 3.1   $ 3.1    
Sales Revenue, Goods, Net | Customer One [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage 16.00% 15.00% 15.00% 15.00%  
Sales Revenue, Goods, Net | Customer Two [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage 17.00%   14.00%    
Accounts Receivable | Customer One [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage     16.00%   20.00%
Accounts Receivable | Customer Two [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage     24.00%