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Marketable Securities - Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value of Available-For-Sale Securities (Detail) - USD ($)
$ in Thousands
Apr. 30, 2024
Jan. 31, 2024
Apr. 30, 2023
Schedule of Available-for-sale Securities [Line Items]      
Short-term Investments, Fair Value $ 312,558 $ 286,744 $ 209,777
Long-term Investments, Fair Value 287,178 314,152 86,156
Amortized Cost 603,407 600,636 300,719
Unrealized Gains 478 2,323 165
Unrealized (Losses) (4,149) (2,063) (4,951)
Fair Value 599,736 600,896 295,933
Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 314,086 288,100 211,580
Unrealized Gains 7 71 2
Unrealized (Losses) (1,535) (1,427) (1,805)
Fair Value 312,558 286,744 209,777
Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 289,321 312,536 89,139
Unrealized Gains 471 2,252 163
Unrealized (Losses) (2,614) (636) (3,146)
Fair Value 287,178 314,152 86,156
Corporate Bonds | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 145,891 123,418 86,052
Unrealized Gains 3 27 1
Unrealized (Losses) (1,000) (883) (1,214)
Fair Value 144,894 122,562 84,839
Corporate Bonds | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 119,907 147,924 42,823
Unrealized Gains 19 441 17
Unrealized (Losses) (1,116) (388) (2,141)
Fair Value 118,810 147,977 40,699
Municipal and Pre-Refunded Municipal Bonds | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 49,515 47,915 45,467
Unrealized Gains 4 9 0
Unrealized (Losses) (204) (414) (547)
Fair Value 49,315 47,510 44,920
Municipal and Pre-Refunded Municipal Bonds | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 38,785 39,243 19,071
Unrealized Gains 9 160 5
Unrealized (Losses) (286) (35) (906)
Fair Value 38,508 39,368 18,170
Commercial Paper | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 2,991 10,557 35,874
Unrealized Gains 0 0 0
Unrealized (Losses) 0 0 0
Fair Value 2,991 10,557 35,874
US Treasury Securities | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 28,925 27,231 22,903
Unrealized Gains 0 0 1
Unrealized (Losses) (127) (36) (16)
Fair Value 28,798 27,195 22,888
US Treasury Securities | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 49,943 34,604  
Unrealized Gains 0 169  
Unrealized (Losses) (677) (26)  
Fair Value 49,266 34,747  
Federal Government Agencies | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 76,515 68,730 21,284
Unrealized Gains 0 35 0
Unrealized (Losses) (204) (94) (28)
Fair Value 76,311 68,671 21,256
Federal Government Agencies | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 53,486 65,698 14,340
Unrealized Gains 0 138 9
Unrealized (Losses) (502) (94) (37)
Fair Value 52,984 65,742 14,312
Mutual Funds, Held in Rabbi Trust | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 15,950 13,817 12,656
Unrealized Gains 443 1,344 132
Unrealized (Losses) (33) (93) (62)
Fair Value 16,360 15,068 12,726
Certificates of Deposit | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 10,249 10,249  
Unrealized Gains 0 0  
Unrealized (Losses) 0 0  
Fair Value 10,249 10,249  
Certificates of Deposit | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 11,250 11,250 249
Unrealized Gains 0 0 0
Unrealized (Losses) 0 0 0
Fair Value $ 11,250 $ 11,250 $ 249