Fair value measurements - Summary of Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Jul. 31, 2020	Jan. 31, 2020
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Money market mutual funds		$ 86,600
Foreign currency derivative contracts		58
Total assets		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		86,600
Foreign currency derivative contracts		0
Total assets		86,600
Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Money market mutual funds		0
Foreign currency derivative contracts		58
Total assets		58
Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Money market mutual funds		0
Foreign currency derivative contracts		0
Total assets		$ 0
Fair Value, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Money market mutual funds	$ 62,494
Total assets	62,494
Foreign currency derivative contracts	(99)
Total liabilities	(99)
Fair Value, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Money market mutual funds	62,494
Total assets	62,494
Foreign currency derivative contracts	0
Total liabilities	0
Fair Value, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Money market mutual funds	0
Total assets	0
Foreign currency derivative contracts	(99)
Total liabilities	(99)
Fair Value, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Money market mutual funds	0
Total assets	0
Foreign currency derivative contracts	0
Total liabilities	$ 0