Fair value measurements - Summary of Fair Value Hierarchy (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Oct. 31, 2020	Jan. 31, 2020
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Money market mutual funds	$ 237,499	$ 86,600
Foreign currency derivative contracts	34	58
Total assets	237,533	86,658
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Money market mutual funds	237,499	86,600
Foreign currency derivative contracts	0	0
Total assets	237,499	86,600
Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Money market mutual funds	0	0
Foreign currency derivative contracts	34	58
Total assets	34	58
Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Money market mutual funds	0	0
Foreign currency derivative contracts	0	0
Total assets	$ 0	$ 0