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Fair Value Measurements - Fair Value of Marketable Securities (Details)
$ in Thousands
Jan. 31, 2021
USD ($)
securities
Jan. 31, 2020
USD ($)
securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total available-for-sale securities $ 584,479 $ 820,092
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | securities 42 0
Available-for-sale securities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Due in one year or less $ 207,450  
Due in one to two years 92,717  
Total available-for-sale securities $ 300,167