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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, 2025
Jan. 31, 2025
Apr. 30, 2024
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost $ 650,489 $ 728,147 $ 603,407
Unrealized Gains 2,227 3,049 478
Unrealized (Losses) (1,194) (1,039) (4,149)
Fair Value 651,522 730,157 599,736
Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 285,605 319,855 314,086
Unrealized Gains 167 228 7
Unrealized (Losses) (187) (134) (1,535)
Fair Value 285,585 319,949 312,558
Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 364,884 408,292 289,321
Unrealized Gains 2,060 2,821 471
Unrealized (Losses) (1,007) (905) (2,614)
Fair Value 365,937 410,208 287,178
Corporate Bonds | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 181,973 186,732 145,891
Unrealized Gains 102 103 3
Unrealized (Losses) (170) (114) (1,000)
Fair Value 181,905 186,721 144,894
Corporate Bonds | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 203,858 233,418 119,907
Unrealized Gains 915 298 19
Unrealized (Losses) (108) (500) (1,116)
Fair Value 204,665 233,216 118,810
US Treasury Securities | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 3,952 5,415 28,925
Unrealized Gains 0 0 0
Unrealized (Losses) (3) (5) (127)
Fair Value 3,949 5,410 28,798
US Treasury Securities | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 87,179 92,852 49,943
Unrealized Gains 989 226 0
Unrealized (Losses) 0 (90) (677)
Fair Value 88,168 92,988 49,266
Federal Government Agencies | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 38,187 53,663 76,515
Unrealized Gains 29 55 0
Unrealized (Losses) (4) (7) (204)
Fair Value 38,212 53,711 76,311
Federal Government Agencies | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 46,308 50,579 53,486
Unrealized Gains 44 16 0
Unrealized (Losses) (90) (292) (502)
Fair Value 46,262 50,303 52,984
Municipal and Pre-Refunded Municipal Bonds | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 43,152 53,772 49,515
Unrealized Gains 36 70 4
Unrealized (Losses) (10) (8) (204)
Fair Value 43,178 53,834 49,315
Municipal and Pre-Refunded Municipal Bonds | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 6,775 14,770 38,785
Unrealized Gains 37 35 9
Unrealized (Losses) (2) (8) (286)
Fair Value 6,810 14,797 38,508
Certificates of Deposit | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 10,499 10,499 10,249
Unrealized Gains 0 0 0
Unrealized (Losses) 0 0 0
Fair Value 10,499 10,499 10,249
Certificates of Deposit | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 1,000 1,000 11,250
Unrealized Gains 0 0 0
Unrealized (Losses) 0 0 0
Fair Value 1,000 1,000 11,250
Commercial Paper | Short-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 7,842 9,774 2,991
Unrealized Gains 0 0 0
Unrealized (Losses) 0 0 0
Fair Value 7,842 9,774 2,991
Mutual Funds, Held in Rabbi Trust | Long-term Investments      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 19,764 15,673 15,950
Unrealized Gains 75 2,246 443
Unrealized (Losses) (807) (15) (33)
Fair Value $ 19,032 $ 17,904 $ 16,360