Fair Value - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jul. 31, 2024	Jan. 31, 2024	Jul. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets accounted for at fair value on a recurring basis	$ 561,829	$ 600,896	$ 373,188
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	561,829	600,896	373,188
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	17,693	15,068	13,898
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	544,136	585,828	359,290
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	258,930	270,539	141,754
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	258,930	270,539	141,754
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	109,279	134,413	91,574
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	109,279	134,413	91,574
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	79,197	61,942	21,553
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	79,197	61,942	21,553
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	72,326	86,878	61,191
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	72,326	86,878	61,191
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	21,499	21,499	1,499
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	21,499	21,499	1,499
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	17,693	15,068	13,898
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	17,693	15,068	13,898
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	2,905	10,557	41,719
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	$ 2,905	$ 10,557	$ 41,719

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