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Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Jan. 31, 2023
Jan. 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 $ 284,222 $ 462,977
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 284,222 462,977
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 11,978 11,813
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 272,244 451,164
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 141,534 231,215
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 141,534 231,215
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 69,741 188,334
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 69,741 188,334
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 11,978 11,813
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 11,978 11,813
Fair Value, Measurements, Recurring | Mutual Funds, Held in Rabbi Trust | 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  
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 23,552 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 23,552 20,137
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 21,636 10,884
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 21,636 10,884
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 15,532 345
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 15,532 345
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 249 249
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 $ 249