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Earnings per share - Additional Information (Detail) - shares
3 Months Ended 6 Months Ended
Apr. 30, 2018
Apr. 30, 2017
Apr. 30, 2018
Apr. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 475,105 1,003,854 563,838 1,003,854