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Marketable Securities (Tables) | 3 Months Ended
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Apr. 30, 2021
Investments Debt And Equity Securities [Abstract] |
Amortized Cost, Gross Unrealized Gains (Losses) and Fair Value of Available-For-Sale Securities | The amortized cost, gross unrealized gains (losses) and fair value of available-for-sale securities by major security type and class of security as of April 30, 2021, January 31, 2021 and April 30, 2020 were as follows:
|  | Amortized |  |  | Unrealized |  |  | Unrealized |  |  | Fair |
|  | Cost |  |  | Gains |  |  | (Losses) |  |  | Value |
As of April 30, 2021 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and pre-refunded municipal bonds |  | $ | 106,266 |  |  | $ | 5 |  |  | $ | (84 | ) |  | $ | 106,187 |
Corporate bonds |  |  | 48,500 |  |  |  | 1 |  |  |  | (49 | ) |  |  | 48,452 |
Commercial paper |  |  | 9,791 |  |  |  | — |  |  |  | — |  |  |  | 9,791 |
|  |  | 164,557 |  |  |  | 6 |  |  |  | (133 | ) |  |  | 164,430 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and pre-refunded municipal bonds |  |  | 40,085 |  |  |  | 17 |  |  |  | (48 | ) |  | $ | 40,054 |
Corporate bonds |  |  | 48,850 |  |  |  | 2 |  |  |  | (111 | ) |  |  | 48,741 |
Mutual funds, held in rabbi trust |  |  | 11,448 |  |  |  | 437 |  |  |  | — |  |  |  | 11,885 |
|  |  | 100,383 |  |  |  | 456 |  |  |  | (159 | ) |  |  | 100,680 |
|  | $ | 264,940 |  |  | $ | 462 |  |  | $ | (292 | ) |  | $ | 265,110 |
As of January 31, 2021 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and pre-refunded municipal bonds |  | $ | 127,097 |  |  | $ | 11 |  |  | $ | (53 | ) |  | $ | 127,055 |
Corporate bonds |  |  | 38,695 |  |  |  | 1 |  |  |  | (48 | ) |  |  | 38,648 |
Commercial paper |  |  | 8,992 |  |  |  | — |  |  |  | — |  |  |  | 8,992 |
|  |  | 174,784 |  |  |  | 12 |  |  |  | (101 | ) |  |  | 174,695 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and pre-refunded municipal bonds |  |  | 53,134 |  |  |  | 17 |  |  |  | (46 | ) |  |  | 53,105 |
Corporate bonds |  |  | 59,890 |  |  |  | 3 |  |  |  | (129 | ) |  |  | 59,764 |
Mutual funds, held in rabbi trust |  |  | 10,827 |  |  |  | 20 |  |  |  | (54 | ) |  |  | 10,793 |
|  |  | 123,851 |  |  |  | 40 |  |  |  | (229 | ) |  |  | 123,662 |
|  | $ | 298,635 |  |  | $ | 52 |  |  | $ | (330 | ) |  | $ | 298,357 |
|  | Amortized |  |  | Unrealized |  |  | Unrealized |  |  | Fair |
|  | Cost |  |  | Gains |  |  | (Losses) |  |  | Value |
As of April 30, 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and pre-refunded municipal bonds |  | $ | 50,887 |  |  | $ | 5 |  |  | $ | (31 | ) |  | $ | 50,861 |
Corporate bonds |  |  | 14,246 |  |  |  | 21 |  |  |  | (7 | ) |  |  | 14,260 |
|  |  | 65,133 |  |  |  | 26 |  |  |  | (38 | ) |  |  | 65,121 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and pre-refunded municipal bonds |  |  | 2,350 |  |  |  | 21 |  |  |  | (1 | ) |  |  | 2,370 |
Corporate bonds |  |  | 2,572 |  |  |  | 3 |  |  |  | (4 | ) |  |  | 2,571 |
Mutual funds, held in rabbi trust |  |  | 7,400 |  |  |  | 682 |  |  |  | — |  |  |  | 8,082 |
Certificates of deposit |  |  | 249 |  |  |  | — |  |  |  | — |  |  |  | 249 |
|  |  | 12,571 |  |  |  | 706 |  |  |  | (5 | ) |  |  | 13,272 |
|  | $ | 77,704 |  |  | $ | 732 |  |  | $ | (43 | ) |  | $ | 78,393 |

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