Background and liquidity (Detail) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		6 Months Ended	9 Months Ended
	Oct. 23, 2020	Dec. 17, 2019	Jul. 22, 2019	Oct. 31, 2020	Jul. 31, 2019	Jan. 31, 2020	Oct. 31, 2020	Oct. 31, 2019
Background And Liquidity [Line Items]
Issuance of common stock in public offering, net of issuance costs (in shares)	5,750,000
Issue price per share (in dollars per share)	$ 32.00
Proceeds from initial public offering							$ 174,800	$ 130,781
Deferred offering costs							$ 226	$ 5,944
Conversion of preferred stock into common stock and cancellation of redeemable preferred stock (in shares)						757,625
Proceeds from secondary offering	$ 174,510
Number of months the company have sufficient to fund its operations							12 months
Common Stock
Background And Liquidity [Line Items]
Issuance of common stock in public offering, net of issuance costs (in shares)		7,762,500		5,750,000	7,812,500
Deferred offering costs		$ 1,047
Conversion of preferred stock into common stock and cancellation of redeemable preferred stock (in shares)			25,311,525		25,311,535
IPO
Background And Liquidity [Line Items]
Issuance of common stock in public offering, net of issuance costs (in shares)			7,812,500
Issue price per share (in dollars per share)			$ 18.00
Proceeds from initial public offering			$ 130,781
Underwriting discounts and commission			9,844
IPO | Common Stock
Background And Liquidity [Line Items]
Deferred offering costs			$ 6,412
IPO | Certain Selling Stockholders
Background And Liquidity [Line Items]
Issuance of common stock in public offering, net of issuance costs (in shares)			2,868,923