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Fair Value Measurements - Assets and liabilities measured at fair value on recurring basis (Detail) - USD ($)
$ in Thousands
Apr. 30, 2021
Jan. 31, 2021
Jan. 31, 2020
Jan. 31, 2019
Debt Securities, Available-for-sale [Line Items]        
Cash and cash equivalents $ 609,809 $ 145,491 $ 72,753 $ 205,238
Short term investments     47,037  
Fair Value, Recurring [Member]        
Debt Securities, Available-for-sale [Line Items]        
Amortized Cost   145,491 119,767  
Gross Unreal Gains     23  
Gross Unreal Losses   0 0  
Fair Value   145,491 119,790  
Cash and cash equivalents   145,491 72,753  
Short term investments     47,037  
Fair Value, Recurring [Member] | Cash [Member]        
Debt Securities, Available-for-sale [Line Items]        
Amortized Cost   35,788 33,266  
Gross Unreal Losses   0 0  
Fair Value   35,788 33,266  
Cash and cash equivalents   35,788 33,266  
Level 1 | Fair Value, Recurring [Member] | Money Market Funds [Member]        
Debt Securities, Available-for-sale [Line Items]        
Amortized Cost   109,703 39,487  
Gross Unreal Losses   0 0  
Fair Value   109,703 39,487  
Cash and cash equivalents   $ 109,703 39,487  
Level 2 | Fair Value, Recurring [Member] | US Treasury Bill Securities [Member]        
Debt Securities, Available-for-sale [Line Items]        
Amortized Cost     47,014  
Gross Unreal Gains     23  
Gross Unreal Losses     0  
Fair Value     47,037  
Short term investments     $ 47,037