Background and liquidity (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		12 Months Ended
	Dec. 17, 2019	Jul. 22, 2019	Apr. 30, 2020	Apr. 30, 2019	Jan. 31, 2020
Background And Liquidity [Line Items]
Deferred offering costs			$ 0	$ 378
Conversion and exercise of preferred stock warrants (in shares)					757,625
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 initial public offering, net of issuance costs (in shares)	7,762,500
Deferred offering costs	$ 1,047
Conversion and exercise of preferred stock warrants (in shares)		25,311,525
IPO
Background And Liquidity [Line Items]
Issuance of common stock in initial 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 initial public offering, net of issuance costs (in shares)		2,868,923