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Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value of Available-For-Sale Securities (Detail) - USD ($)
$ in Thousands
Jul. 31, 2022
Jan. 31, 2022
Jul. 31, 2021
Schedule of Available-for-sale Securities [Line Items]      
Short-term Investments, Amortized Cost $ 161,919 $ 239,929 $ 157,077
Short-term Investments, Unrealized Gains   2 16
Short-term Investments, Unrealized (Losses) (1,899) (511) (111)
Short-term Investments, Fair Value 160,020 239,420 156,982
Long-term Investments, Amortized Cost 159,712 227,603 113,325
Long-term Investments, Unrealized Gains   1 181
Long-term Investments, Unrealized (Losses) (7,184) (4,047) (257)
Long-term Investments, Fair Value 152,528 223,557 113,249
Amortized Cost 321,631 467,532 270,402
Unrealized Gains   3 197
Unrealized (Losses) (9,083) (4,558) (368)
Fair Value 312,548 462,977 270,231
Corporate Bonds      
Schedule of Available-for-sale Securities [Line Items]      
Short-term Investments, Amortized Cost 76,652 85,062 28,808
Short-term Investments, Unrealized Gains   1 2
Short-term Investments, Unrealized (Losses) (1,211) (200) (24)
Short-term Investments, Fair Value 75,441 84,863 28,786
Long-term Investments, Amortized Cost 96,086 148,830 61,646
Long-term Investments, Unrealized Gains     4
Long-term Investments, Unrealized (Losses) (4,160) (2,478) (159)
Long-term Investments, Fair Value 91,926 146,352 61,491
Municipal and Pre-Refunded Municipal Bonds      
Schedule of Available-for-sale Securities [Line Items]      
Short-term Investments, Amortized Cost 75,518 128,984 122,173
Short-term Investments, Unrealized Gains   1 14
Short-term Investments, Unrealized (Losses) (595) (273) (87)
Short-term Investments, Fair Value 74,923 128,712 122,100
Long-term Investments, Amortized Cost 47,437 60,533 40,069
Long-term Investments, Unrealized Gains   1 34
Long-term Investments, Unrealized (Losses) (1,858) (912) (56)
Long-term Investments, Fair Value 45,579 59,622 40,047
US Treasury Securities      
Schedule of Available-for-sale Securities [Line Items]      
Short-term Investments, Amortized Cost 9,749 14,999  
Short-term Investments, Unrealized (Losses) (93) (38)  
Short-term Investments, Fair Value 9,656 14,961  
Long-term Investments, Amortized Cost 3,229 5,222  
Long-term Investments, Unrealized (Losses) (129) (46)  
Long-term Investments, Fair Value 3,100 5,176  
Commercial Paper      
Schedule of Available-for-sale Securities [Line Items]      
Short-term Investments, Amortized Cost   10,884 6,096
Short-term Investments, Fair Value   10,884 6,096
Mutual Funds, Held in Rabbi Trust      
Schedule of Available-for-sale Securities [Line Items]      
Long-term Investments, Amortized Cost 12,361 12,419 11,610
Long-term Investments, Unrealized Gains     143
Long-term Investments, Unrealized (Losses) (1,025) (606) (42)
Long-term Investments, Fair Value 11,336 11,813 $ 11,711
Federal Government Agencies      
Schedule of Available-for-sale Securities [Line Items]      
Long-term Investments, Amortized Cost 350 350  
Long-term Investments, Unrealized (Losses) (12) (5)  
Long-term Investments, Fair Value 338 345  
Certificates of Deposit      
Schedule of Available-for-sale Securities [Line Items]      
Long-term Investments, Amortized Cost 249 249  
Long-term Investments, Fair Value $ 249 $ 249