Income taxes - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Oct. 31, 2018	Oct. 31, 2017
Income Taxes [Line Items]
Provision for income tax as percentage of income (loss) before income taxes	21.00%	16.00%
Unrecognized tax benefits	$ 65,000		$ 58,000
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%	35.00%
Income Tax Expense (Benefit)	$ 168,000	$ 56,000