Fair Value - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jul. 31, 2025	Jan. 31, 2025	Jul. 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	$ 657,000	$ 730,157	$ 561,829
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	657,000	730,157	561,829
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	20,376	17,904	17,693
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	636,624	712,253	544,136
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	406,811	419,937	258,930
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	406,811	419,937	258,930
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	70,079	104,014	109,279
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	70,079	104,014	109,279
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	97,520	98,398	79,197
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	97,520	98,398	79,197
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	53,037	68,631	72,326
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	53,037	68,631	72,326
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	1,249	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	1,249	11,499	21,499
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	20,376	17,904	17,693
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	20,376	17,904	17,693
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	7,928	9,774	2,905
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	$ 7,928	$ 9,774	$ 2,905

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