Income taxes - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Income Taxes [Line Items]
Provision for income tax as percentage of income (loss) before income taxes	18.00%	30.00%
Unrecognized tax benefits	$ 0			$ 0
Accrued interest and penalties related to uncertain tax positions	0			$ 0
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				35.00%
Increase (Decrease) in Deferred Liabilities	41,000
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	41,000
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Amount	$ 19,000
Scenario, Plan [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%