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						9 Months Ended
	Oct. 31, 2020	Jul. 31, 2020	Apr. 30, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Oct. 31, 2020	Oct. 31, 2019
Numerator:
Net loss	$ (6,713)	$ (6,371)	$ (6,112)	$ (2,437)	$ (7,493)	$ (6,695)	$ (19,196)	$ (16,625)
Preferred stock dividend paid	0			0			0	(14,955)
Accretion of redeemable convertible preferred stock to redemption value	0			0			0	(56,175)
Net loss attributable to common stockholders	$ (6,713)			$ (2,437)			$ (19,196)	$ (87,755)
Denominator:
Weighted-average shares of common stock outstanding, basic and diluted (in shares)	38,511,370			35,790,951			37,855,503	15,007,247
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.17)			$ (0.07)			$ (0.51)	$ (5.85)