Income taxes (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019
Income Tax Disclosure [Abstract]
Income tax provision	$ 66,000	$ 51,000	$ 177,000	$ 119,000
Effective tax rate			(1.40%)	(0.80%)