Fair Value - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Oct. 31, 2025	Jan. 31, 2025	Oct. 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	$ 656,976	$ 730,157	$ 580,682
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	656,976	730,157	580,682
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	22,034	17,904	17,789
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	634,942	712,253	562,893
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	454,374	419,937	288,870
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	454,374	419,937	288,870
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	44,330	104,014	107,478
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	44,330	104,014	107,478
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	94,940	98,398	61,141
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	94,940	98,398	61,141
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	37,302	68,631	80,962
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	37,302	68,631	80,962
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	1,000	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	1,000	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	22,034	17,904	17,789
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	22,034	17,904	17,789
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	2,996	9,774	2,943
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	$ 2,996	$ 9,774	$ 2,943

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