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Fair Value Measurements (Details) - USD ($) $ in Thousands | Jul. 31, 2018 | Jul. 31, 2017
--- | --- | ---
Available-for-sale securities: |  |
Marketable securities | $ 5,972 | $ 58,272
Rafael convertible promissory notes |  | 6,300
Total |  | 64,572
Fair Value Measurements, Recurring basis [Member] | Level 1 [Member] |  |
Available-for-sale securities: |  |
Marketable securities | 2,052 | 12,151
Rafael convertible promissory notes |  |
Total |  | 12,151
Fair Value Measurements, Recurring basis [Member] | Level 2 [Member] |  |
Available-for-sale securities: |  |
Marketable securities | 3,920 | 46,121
Rafael convertible promissory notes |  |
Total |  | 46,121
Fair Value Measurements, Recurring basis [Member] | Level 3 [Member] |  |
Available-for-sale securities: |  |
Marketable securities |  |
Rafael convertible promissory notes |  | 6,300
Total |  | $ 6,300

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