Fair value measurements (Details) - USD ($) $ in Thousands	Apr. 30, 2020	Jan. 31, 2020
Money market funds | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of money market funds	$ 62,492
Prepaid and other current assets | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of foreign currency contracts, assets		$ 58
Accrued expenses | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of foreign currency contracts, liabilities	$ 603