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Marketable Securities - Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value of Available-For-Sale Securities (Detail) - USD ($)
$ in Thousands
Jan. 31, 2025
Jan. 31, 2024
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 728,147 $ 600,636
Unrealized Gains 3,049 2,323
Unrealized (Losses) (1,039) (2,063)
Fair Value 730,157 600,896
Long-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 408,292 312,536
Unrealized Gains 2,821 2,252
Unrealized (Losses) (905) (636)
Fair Value 410,208 314,152
Short-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 319,855 288,100
Unrealized Gains 228 71
Unrealized (Losses) (134) (1,427)
Fair Value 319,949 286,744
Municipal And Pre-Refunded Municipal Bonds | Long-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 14,770 39,243
Unrealized Gains 35 160
Unrealized (Losses) (8) (35)
Fair Value 14,797 39,368
Municipal And Pre-Refunded Municipal Bonds | Short-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 53,772 47,915
Unrealized Gains 70 9
Unrealized (Losses) (8) (414)
Fair Value 53,834 47,510
Corporate Bonds | Long-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 233,418 147,924
Unrealized Gains 298 441
Unrealized (Losses) (500) (388)
Fair Value 233,216 147,977
Corporate Bonds | Short-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 186,732 123,418
Unrealized Gains 103 27
Unrealized (Losses) (114) (883)
Fair Value 186,721 122,562
US Treasury Securities | Long-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 92,852 34,604
Unrealized Gains 226 169
Unrealized (Losses) (90) (26)
Fair Value 92,988 34,747
US Treasury Securities | Short-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 5,415 27,231
Unrealized Gains 0 0
Unrealized (Losses) (5) (36)
Fair Value 5,410 27,195
Commercial Paper | Short-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 9,774 10,557
Unrealized Gains 0 0
Unrealized (Losses) 0 0
Fair Value 9,774 10,557
Mutual Funds, Held in Rabbi Trust | Long-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 15,673 13,817
Unrealized Gains 2,246 1,344
Unrealized (Losses) (15) (93)
Fair Value 17,904 15,068
Federal Government Agencies | Long-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 50,579 65,698
Unrealized Gains 16 138
Unrealized (Losses) (292) (94)
Fair Value 50,303 65,742
Federal Government Agencies | Short-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 53,663 68,730
Unrealized Gains 55 35
Unrealized (Losses) (7) (94)
Fair Value 53,711 68,671
Certificates of Deposit | Long-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,000 11,250
Unrealized Gains 0 0
Unrealized (Losses) 0 0
Fair Value 1,000 11,250
Certificates of Deposit | Short-term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 10,499 10,249
Unrealized Gains 0 0
Unrealized (Losses) 0 0
Fair Value $ 10,499 $ 10,249