Income taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2019	Apr. 30, 2018	Oct. 31, 2018	Oct. 31, 2017
Income Taxes [Line Items]
Provision for income tax as percentage of income (loss) before income taxes	23.00%	20.00%	22.00%	20.00%
Unrecognized tax benefits	$ 90,000		$ 90,000		$ 58,000
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%	35.00%
Income Tax Expense (Benefit)	$ 315,000	$ 799,000	$ 483,000	$ 855,000