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Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Oct. 31, 2021
Jan. 31, 2021
Oct. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis $ 458,155 $ 298,357 $ 9,352
Fair Value, Measurements, Recurring      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 458,155 298,357 9,352
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 34,016 10,793 9,352
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 424,139 287,564  
Fair Value, Measurements, Recurring | Corporate Bonds      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 227,436 98,412 32
Fair Value, Measurements, Recurring | Corporate Bonds | Fair Value, Inputs, Level 1      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis     32
Fair Value, Measurements, Recurring | Corporate Bonds | Fair Value, Inputs, Level 2      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 227,436 98,412  
Fair Value, Measurements, Recurring | Municipal And Pre-Refunded Municipal Bonds      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 193,355 180,160 54
Fair Value, Measurements, Recurring | Municipal And Pre-Refunded Municipal Bonds | Fair Value, Inputs, Level 1      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis     54
Fair Value, Measurements, Recurring | Municipal And Pre-Refunded Municipal Bonds | Fair Value, Inputs, Level 2      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 193,355 180,160  
Fair Value, Measurements, Recurring | Treasury Bills      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 21,587    
Fair Value, Measurements, Recurring | Treasury Bills | Fair Value, Inputs, Level 1      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 21,587    
Fair Value, Measurements, Recurring | Mutual Funds, Held in Rabbi Trust      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 12,081 10,793 9,266
Fair Value, Measurements, Recurring | Mutual Funds, Held in Rabbi Trust | Fair Value, Inputs, Level 1      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 12,081 10,793 $ 9,266
Fair Value, Measurements, Recurring | Commercial Paper      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 3,099 8,992  
Fair Value, Measurements, Recurring | Commercial Paper | Fair Value, Inputs, Level 2      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 3,099 $ 8,992  
Fair Value, Measurements, Recurring | Federal Government Agencies      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 348    
Fair Value, Measurements, Recurring | Federal Government Agencies | Fair Value, Inputs, Level 1      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 348    
Fair Value, Measurements, Recurring | Certificates of Deposit      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 249    
Fair Value, Measurements, Recurring | Certificates of Deposit | Fair Value, Inputs, Level 2      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis $ 249