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Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Jan. 31, 2022
Jan. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial assets accounted for at fair value on a recurring basis $ 462,977 $ 298,357
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 462,977 298,357
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 11,813 10,793
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 451,164 287,564
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 231,215 98,412
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 231,215 98,412
Fair Value, Measurements, Recurring | Municipal and Pre-funded 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 188,334  
Fair Value, Measurements, Recurring | Municipal and Pre-funded 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 188,334  
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 20,137  
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 20,137  
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 11,813 10,793
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 11,813 10,793
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 10,884 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 10,884 8,992
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  
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 345  
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 $ 345  
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   180,160
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   $ 180,160