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Marketable Securities (Tables) | 6 Months Ended
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Jul. 31, 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 July 31, 2019, January 31, 2019 and July 31, 2018 were as follows:
|  | Amortized |  |  | Unrealized |  |  | Unrealized |  |  | Fair |
|  | Cost |  |  | Gains |  |  | (Losses) |  |  | Value |
As of July 31, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 125,943 |  |  | $ | 190 |  |  | $ | (31 | ) |  | $ | 126,102 |
Municipal and pre-refunded municipal bonds |  |  | 42,023 |  |  |  | 40 |  |  |  | (9 | ) |  |  | 42,054 |
Certificates of deposit |  |  | 1,745 |  |  |  | — |  |  |  | — |  |  |  | 1,745 |
Federal government agencies |  |  | 1,495 |  |  |  | 2 |  |  |  | — |  |  |  | 1,497 |
|  |  | 171,206 |  |  |  | 232 |  |  |  | (40 | ) |  |  | 171,398 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  |  | 49,385 |  |  |  | 174 |  |  |  | (33 | ) |  |  | 49,526 |
Municipal and pre-refunded municipal bonds |  |  | 19,526 |  |  |  | 6 |  |  |  | (50 | ) |  |  | 19,482 |
Mutual funds, held in rabbi trust |  |  | 7,826 |  |  |  | 56 |  |  |  | (7 | ) |  |  | 7,875 |
Certificates of deposit |  |  | 1,847 |  |  |  | — |  |  |  | — |  |  |  | 1,847 |
Federal government agencies |  |  | 126 |  |  |  | 1 |  |  |  | — |  |  |  | 127 |
|  |  | 78,710 |  |  |  | 237 |  |  |  | (90 | ) |  |  | 78,857 |
|  | $ | 249,916 |  |  | $ | 469 |  |  | $ | (130 | ) |  | $ | 250,255 |
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 |
Certificates of deposit |  |  | 1,050 |  |  |  | — |  |  |  | — |  |  |  | 1,050 |
Federal government agencies |  |  | 1,458 |  |  |  | — |  |  |  | — |  |  |  | 1,458 |
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 |
Certificates of deposit |  |  | 2,143 |  |  |  | — |  |  |  | — |  |  |  | 2,143 |
Federal government agencies |  |  | 6,603 |  |  |  | 2 |  |  |  | (1 | ) |  |  | 6,604 |
|  |  | 56,866 |  |  |  | 493 |  |  |  | (67 | ) |  |  | 57,292 |
|  | $ | 336,292 |  |  | $ | 532 |  |  | $ | (300 | ) |  | $ | 336,524 |
|  | Amortized |  |  | Unrealized |  |  | Unrealized |  |  | Fair |
|  | Cost |  |  | Gains |  |  | (Losses) |  |  | Value |
As of July 31, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 150,648 |  |  | $ | — |  |  | $ | (261 | ) |  | $ | 150,387 |
Municipal and pre-refunded municipal bonds |  |  | 46,904 |  |  |  | 10 |  |  |  | (43 | ) |  |  | 46,871 |
Certificates of deposit |  |  | 908 |  |  |  | — |  |  |  | — |  |  |  | 908 |
|  |  | 198,460 |  |  |  | 10 |  |  |  | (304 | ) |  |  | 198,166 |
Long-term Investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  |  | 34,333 |  |  |  | — |  |  |  | (213 | ) |  |  | 34,120 |
Municipal and pre-refunded municipal bonds |  |  | 2,130 |  |  |  | 1 |  |  |  | (7 | ) |  |  | 2,124 |
Mutual funds, held in rabbi trust |  |  | 6,401 |  |  |  | 171 |  |  |  | (1 | ) |  |  | 6,571 |
Certificates of deposit |  |  | 2,699 |  |  |  | — |  |  |  | — |  |  |  | 2,699 |
|  |  | 45,563 |  |  |  | 172 |  |  |  | (221 | ) |  |  | 45,514 |
|  | $ | 244,023 |  |  | $ | 182 |  |  | $ | (525 | ) |  | $ | 243,680 |

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