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Fair Value - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Jul. 31, 2023
Jan. 31, 2023
Jul. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis $ 373,188 $ 284,222 $ 312,548
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 373,188 284,222 312,548
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 13,898 11,978 11,336
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 359,290 272,244 301,212
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 141,754 141,534 167,367
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 141,754 141,534 167,367
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 61,191 69,741 120,502
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 61,191 69,741 120,502
Fair Value, Measurements, Recurring | US Treasury Securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Financial assets accounted for at fair value on a recurring basis 21,553 23,552 12,756
Fair Value, Measurements, Recurring | US Treasury Securities | 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 21,553 23,552  
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 13,898 11,978 11,336
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 13,898 11,978 11,336
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 41,719 21,636  
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 41,719 21,636  
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 91,574 15,532 338
Fair Value, Measurements, Recurring | Federal Government Agencies | 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 91,574 15,532 338
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 1,499 249 249
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 $ 1,499 $ 249 $ 249