Fair Value - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jan. 31, 2025	Jan. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets accounted for at fair value on a recurring basis	$ 730,157	$ 600,896
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	730,157	600,896
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	17,904	15,068
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	712,253	585,828
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	419,937	270,539
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	419,937	270,539
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	68,631	86,878
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	68,631	86,878
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	17,904	15,068
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	17,904	15,068
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	98,398	61,942
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	98,398	61,942
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	9,774	10,557
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	9,774	10,557
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	104,014	134,413
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	104,014	134,413
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	11,499	21,499
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	$ 11,499	$ 21,499

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]