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Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value of Available-For-Sale Securities (Detail) - USD ($)
$ in Thousands
Jan. 31, 2022
Jan. 31, 2021
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 467,532 $ 298,635
Unrealized Gains 3 52
Unrealized (Losses) (4,558) (330)
Fair Value 462,977 298,357
Short-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 239,929 174,784
Unrealized Gains 2 12
Unrealized (Losses) (511) (101)
Fair Value 239,420 174,695
Short-term Investments | Municipal And Pre-Refunded Municipal Bonds    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 128,984 127,097
Unrealized Gains 1 11
Unrealized (Losses) (273) (53)
Fair Value 128,712 127,055
Short-term Investments | Corporate Bonds    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 85,062 38,695
Unrealized Gains 1 1
Unrealized (Losses) (200) (48)
Fair Value 84,863 38,648
Short-term Investments | US Treasury Securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 14,999  
Unrealized (Losses) (38)  
Fair Value 14,961  
Short-term Investments | Commercial Paper    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 10,884 8,992
Fair Value 10,884 8,992
Long-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 227,603 123,851
Unrealized Gains 1 40
Unrealized (Losses) (4,047) (229)
Fair Value 223,557 123,662
Long-term Investments | Municipal And Pre-Refunded Municipal Bonds    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 60,533 53,134
Unrealized Gains 1 17
Unrealized (Losses) (912) (46)
Fair Value 59,622 53,105
Long-term Investments | Corporate Bonds    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 148,830 59,890
Unrealized Gains   3
Unrealized (Losses) (2,478) (129)
Fair Value 146,352 59,764
Long-term Investments | US Treasury Securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 5,222  
Unrealized (Losses) (46)  
Fair Value 5,176  
Long-term Investments | Mutual Funds, Held in Rabbi Trust    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 12,419 10,827
Unrealized Gains   20
Unrealized (Losses) (606) (54)
Fair Value 11,813 $ 10,793
Long-term Investments | Federal Government Agencies    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 350  
Unrealized (Losses) (5)  
Fair Value 345  
Long-term Investments | Certificates of Deposit    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 249  
Fair Value $ 249