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Marketable Securities (Tables) | 3 Months Ended
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Apr. 30, 2019
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, 2019, January 31, 2019 and April 30, 2018 were as follows:
|  | Amortized |  |  | Unrealized |  |  | Unrealized |  |  | Fair |
|  | Cost |  |  | Gains |  |  | (Losses) |  |  | Value |
As of April 30, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 169,627 |  |  | $ | 72 |  |  | $ | (70 | ) |  | $ | 169,629 |
Municipal and pre-refunded municipal bonds |  |  | 52,131 |  |  |  | 23 |  |  |  | (6 | ) |  |  | 52,148 |
Federal government agencies |  |  | 2,735 |  |  |  | 4 |  |  |  | — |  |  |  | 2,739 |
Certificates of deposit |  |  | 1,650 |  |  |  | — |  |  |  | — |  |  |  | 1,650 |
Commercial paper |  |  | 2,997 |  |  |  | — |  |  |  | — |  |  |  | 2,997 |
|  |  | 229,140 |  |  |  | 99 |  |  |  | (76 | ) |  |  | 229,163 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  |  | 71,105 |  |  |  | 95 |  |  |  | (46 | ) |  |  | 71,154 |
Municipal and pre-refunded municipal bonds |  |  | 11,035 |  |  |  | 11 |  |  |  | (8 | ) |  |  | 11,038 |
Mutual funds, held in rabbi trust |  |  | 7,733 |  |  |  | 208 |  |  |  |  |  |  |  | 7,941 |
Federal government agencies |  |  | 2,351 |  |  |  | 7 |  |  |  | — |  |  |  | 2,358 |
Certificates of deposit |  |  | 1,403 |  |  |  | — |  |  |  | — |  |  |  | 1,403 |
|  |  | 93,627 |  |  |  | 321 |  |  |  | (54 | ) |  |  | 93,894 |
|  | $ | 322,767 |  |  | $ | 420 |  |  | $ | (130 | ) |  | $ | 323,057 |
As of January 31, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 227,287 |  |  | $ | 24 |  |  | $ | (214 | ) |  | $ | 227,097 |
Municipal and pre-refunded municipal bonds |  |  | 43,677 |  |  |  | 15 |  |  |  | (18 | ) |  |  | 43,674 |
Federal government agencies |  |  | 1,458 |  |  |  | — |  |  |  | — |  |  |  | 1,458 |
Certificates of deposit |  |  | 1,050 |  |  |  | — |  |  |  | — |  |  |  | 1,050 |
Commercial paper |  |  | 2,979 |  |  |  | — |  |  |  | — |  |  |  | 2,979 |
Treasury bills |  |  | 2,975 |  |  |  | — |  |  |  | (1 | ) |  |  | 2,974 |
|  |  | 279,426 |  |  |  | 39 |  |  |  | (233 | ) |  |  | 279,232 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  |  | 34,265 |  |  |  | 34 |  |  |  | (63 | ) |  |  | 34,236 |
Municipal and pre-refunded municipal bonds |  |  | 7,554 |  |  |  | 7 |  |  |  | (3 | ) |  |  | 7,558 |
Mutual funds, held in rabbi trust |  |  | 6,301 |  |  |  | 450 |  |  |  | — |  |  |  | 6,751 |
Federal government agencies |  |  | 6,603 |  |  |  | 2 |  |  |  | (1 | ) |  |  | 6,604 |
Certificates of deposit |  |  | 2,143 |  |  |  | — |  |  |  | — |  |  |  | 2,143 |
|  |  | 56,866 |  |  |  | 493 |  |  |  | (67 | ) |  |  | 57,292 |
|  | $ | 336,292 |  |  | $ | 532 |  |  | $ | (300 | ) |  | $ | 336,524 |
|  | Amortized |  |  | Unrealized |  |  | Unrealized |  |  | Fair |
|  | Cost |  |  | Gains |  |  | (Losses) |  |  | Value |
As of April 30, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 110,657 |  |  | $ | — |  |  | $ | (294 | ) |  | $ | 110,363 |
Municipal and pre-refunded municipal bonds |  |  | 54,659 |  |  |  | — |  |  |  | (47 | ) |  |  | 54,612 |
Certificates of deposit |  |  | 1,392 |  |  |  | — |  |  |  | — |  |  |  | 1,392 |
|  |  | 166,708 |  |  |  | — |  |  |  | (341 | ) |  |  | 166,367 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  |  | 18,137 |  |  |  | — |  |  |  | (212 | ) |  |  | 17,925 |
Municipal and pre-refunded municipal bonds |  |  | 7,873 |  |  |  | — |  |  |  | (30 | ) |  |  | 7,843 |
Mutual funds, held in rabbi trust |  |  | 6,453 |  |  |  | 33 |  |  |  | (3 | ) |  |  | 6,483 |
Certificates of deposit |  |  | 2,828 |  |  |  | — |  |  |  | — |  |  |  | 2,828 |
|  |  | 35,291 |  |  |  | 33 |  |  |  | (245 | ) |  |  | 35,079 |
|  | $ | 201,999 |  |  | $ | 33 |  |  | $ | (586 | ) |  | $ | 201,446 |

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