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Marketable Securities (Tables) | 9 Months Ended
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Oct. 31, 2020
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, 2020, January 31, 2020 and October 31, 2019 were as follows:
|  | Amortized |  |  | Unrealized |  |  | Unrealized |  |  | Fair |
|  | Cost |  |  | Gains |  |  | (Losses) |  |  | Value |
As of October 31, 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 2 |  |  | $ | — |  |  | $ | — |  |  | $ | 2 |
|  |  | 2 |  |  |  | — |  |  |  | — |  |  |  | 2 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mutual funds, held in rabbi trust |  |  | 9,393 |  |  |  | 17 |  |  |  | (144 | ) |  |  | 9,266 |
Municipal and pre-refunded municipal bonds |  |  | 53 |  |  |  | 1 |  |  |  | — |  |  |  | 54 |
Corporate bonds |  |  | 30 |  |  |  | — |  |  |  | — |  |  |  | 30 |
|  |  | 9,476 |  |  |  | 18 |  |  |  | (144 | ) |  |  | 9,350 |
|  | $ | 9,478 |  |  | $ | 18 |  |  | $ | (144 | ) |  | $ | 9,352 |
As of January 31, 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and pre-refunded municipal bonds |  | $ | 38,617 |  |  | $ | 20 |  |  | $ | (11 | ) |  | $ | 38,626 |
Corporate bonds |  |  | 166,790 |  |  |  | 318 |  |  |  | (26 | ) |  |  | 167,082 |
Certificates of deposit |  |  | 2,593 |  |  |  | — |  |  |  | — |  |  |  | 2,593 |
Federal government agencies |  |  | 1,152 |  |  |  | 3 |  |  |  | — |  |  |  | 1,155 |
Commercial paper |  |  | 1,997 |  |  |  | — |  |  |  | — |  |  |  | 1,997 |
|  |  | 211,149 |  |  |  | 341 |  |  |  | (37 | ) |  |  | 211,453 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mutual funds, held in rabbi trust |  |  | 8,448 |  |  |  | 36 |  |  |  | (55 | ) |  |  | 8,429 |
Municipal and pre-refunded municipal bonds |  |  | 30,340 |  |  |  | 35 |  |  |  | (17 | ) |  |  | 30,358 |
Corporate bonds |  |  | 47,352 |  |  |  | 205 |  |  |  | (40 | ) |  |  | 47,517 |
Certificates of deposit |  |  | 3,867 |  |  |  | — |  |  |  | — |  |  |  | 3,867 |
Federal government agencies |  |  | 6,926 |  |  |  | 1 |  |  |  | (2 | ) |  |  | 6,925 |
|  |  | 96,933 |  |  |  | 277 |  |  |  | (114 | ) |  |  | 97,096 |
|  | $ | 308,082 |  |  | $ | 618 |  |  | $ | (151 | ) |  | $ | 308,549 |
|  | Amortized |  |  | Unrealized |  |  | Unrealized |  |  | Fair |
|  | Cost |  |  | Gains |  |  | (Losses) |  |  | Value |
As of October 31, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and pre-refunded municipal bonds |  | $ | 39,256 |  |  | $ | 38 |  |  | $ | (14 | ) |  | $ | 39,280 |
Corporate bonds |  |  | 125,040 |  |  |  | 310 |  |  |  | (12 | ) |  |  | 125,338 |
Federal government agencies |  |  | 1,622 |  |  |  | 4 |  |  |  | — |  |  |  | 1,626 |
Certificates of deposit |  |  | 2,466 |  |  |  | — |  |  |  | — |  |  |  | 2,466 |
Commercial paper |  |  | 1,987 |  |  |  | — |  |  |  | — |  |  |  | 1,987 |
|  |  | 170,371 |  |  |  | 352 |  |  |  | (26 | ) |  |  | 170,697 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mutual funds, held in rabbi trust |  |  | 7,661 |  |  |  | 144 |  |  |  | (1 | ) |  |  | 7,804 |
Municipal and pre-refunded municipal bonds |  |  | 20,795 |  |  |  | 13 |  |  |  | (35 | ) |  |  | 20,773 |
Corporate bonds |  |  | 45,556 |  |  |  | 270 |  |  |  | (26 | ) |  |  | 45,800 |
Federal government agencies |  |  | 6,365 |  |  |  | — |  |  |  | (15 | ) |  |  | 6,350 |
Certificates of deposit |  |  | 2,394 |  |  |  | — |  |  |  | — |  |  |  | 2,394 |
|  |  | 82,771 |  |  |  | 427 |  |  |  | (77 | ) |  |  | 83,121 |
|  | $ | 253,142 |  |  | $ | 779 |  |  | $ | (103 | ) |  | $ | 253,818 |

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