Net loss per share attributable to common stockholders - Schedule of earnings per share basic and diluted (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jul. 31, 2020	Apr. 30, 2020	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2020	Jul. 31, 2019
Numerator:
Net loss	$ (6,371)	$ (6,112)	$ (7,493)	$ (6,695)	$ (12,483)	$ (14,188)
Preferred stock dividend paid	0		(14,955)		0	(14,955)
Accretion of redeemable convertible preferred stock to redemption value	0		(48,312)		0	(56,175)
Net loss attributable to common stockholders	$ (6,371)		$ (70,760)		$ (12,483)	$ (85,318)
Denominator:
Weighted-average shares of common stock outstanding, basic and diluted (in shares)	37,735,155		6,793,363		37,523,966	4,443,155
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.17)		$ (10.42)		$ (0.33)	$ (19.20)