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Marketable Securities (Tables) | 9 Months Ended
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Oct. 31, 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 October 31, 2021, January 31, 2021 and October 31, 2020 were as follows:
|  | Amortized |  |  | Unrealized |  |  | Unrealized |  |  | Fair |
|  | Cost |  |  | Gains |  |  | (Losses) |  |  | Value |
As of October 31, 2021 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 53,744 |  |  | $ | 3 |  |  | $ | (71 | ) |  | $ | 53,676 |
Municipal and pre-refunded municipal bonds |  |  | 114,818 |  |  |  | 9 |  |  |  | (73 | ) |  |  | 114,754 |
Treasury bills |  |  | 16,849 |  |  |  | — |  |  |  | (3 | ) |  |  | 16,846 |
Commercial paper |  |  | 3,099 |  |  |  | — |  |  |  | — |  |  |  | 3,099 |
|  |  | 188,510 |  |  |  | 12 |  |  |  | (147 | ) |  |  | 188,375 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  |  | 174,884 |  |  |  | 1 |  |  |  | (1,125 | ) |  | $ | 173,760 |
Municipal and pre-refunded municipal bonds |  |  | 78,955 |  |  |  | 8 |  |  |  | (362 | ) |  |  | 78,601 |
Treasury bills |  |  | 4,748 |  |  |  | — |  |  |  | (7 | ) |  |  | 4,741 |
Mutual funds, held in rabbi trust |  |  | 11,540 |  |  |  | 542 |  |  |  | (1 | ) |  |  | 12,081 |
Federal government agencies |  |  | 350 |  |  |  | — |  |  |  | (2 | ) |  |  | 348 |
Certificates of deposit |  |  | 249 |  |  |  | — |  |  |  | — |  |  |  | 249 |
|  |  | 270,726 |  |  |  | 551 |  |  |  | (1,497 | ) |  |  | 269,780 |
|  | $ | 459,236 |  |  | $ | 563 |  |  | $ | (1,644 | ) |  | $ | 458,155 |
As of January 31, 2021 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 38,695 |  |  | $ | 1 |  |  | $ | (48 | ) |  | $ | 38,648 |
Municipal and pre-refunded municipal bonds |  |  | 127,097 |  |  |  | 11 |  |  |  | (53 | ) |  |  | 127,055 |
Commercial paper |  |  | 8,992 |  |  |  | — |  |  |  | — |  |  |  | 8,992 |
|  |  | 174,784 |  |  |  | 12 |  |  |  | (101 | ) |  |  | 174,695 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  |  | 59,890 |  |  |  | 3 |  |  |  | (129 | ) |  |  | 59,764 |
Municipal and pre-refunded municipal bonds |  |  | 53,134 |  |  |  | 17 |  |  |  | (46 | ) |  |  | 53,105 |
Mutual funds, held in rabbi trust |  |  | 10,827 |  |  |  | 20 |  |  |  | (54 | ) |  |  | 10,793 |
|  |  | 123,851 |  |  |  | 40 |  |  |  | (229 | ) |  |  | 123,662 |
|  | $ | 298,635 |  |  | $ | 52 |  |  | $ | (330 | ) |  | $ | 298,357 |
As of October 31, 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 2 |  |  | $ | — |  |  | $ | — |  |  | $ | 2 |
|  |  | 2 |  |  |  | — |  |  |  | — |  |  |  | 2 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  |  | 30 |  |  |  | — |  |  |  | — |  |  |  | 30 |
Municipal and pre-refunded municipal bonds |  |  | 53 |  |  |  | 1 |  |  |  | — |  |  |  | 54 |
Mutual funds, held in rabbi trust |  |  | 9,393 |  |  |  | 17 |  |  |  | (144 | ) |  |  | 9,266 |
|  |  | 9,476 |  |  |  | 18 |  |  |  | (144 | ) |  |  | 9,350 |
|  | $ | 9,478 |  |  | $ | 18 |  |  | $ | (144 | ) |  | $ | 9,352 |

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