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Marketable Securities (Details) - USD ($) $ in Thousands | Apr. 30, 2018 | Jul. 31, 2017
--- | --- | ---
Available-for-sale securities: |  |  |
Amortized Cost |  | $ 10,549 | $ 58,238
Gross Unrealized Gains, Total |  | 27 | 82
Gross Unrealized Losses, Total |  | (6) | (48)
Fair Value |  | 10,570 | 58,272
Certificates of deposit [Member] |  |  |
Available-for-sale securities: |  |  |
Amortized Cost | [1] | 5,649 | 29,011
Gross Unrealized Gains | [1] |  | 1
Gross Unrealized Losses | [1] |  | (7)
Fair Value | [1] | 5,649 | 29,005
Federal Government Sponsored Enterprise notes [Member] |  |  |
Available-for-sale securities: |  |  |
Amortized Cost |  |  | 3,992
Gross Unrealized Gains |  |  |
Gross Unrealized Losses |  |  | (14)
Fair Value |  |  | 3,978
International agency notes [Member] |  |  |
Available-for-sale securities: |  |  |
Amortized Cost |  |  | 291
Gross Unrealized Gains |  |  |
Gross Unrealized Losses |  |  |
Fair Value |  |  | 291
Mutual funds [Member] |  |  |
Available-for-sale securities: |  |  |
Amortized Cost |  |  | 5,353
Gross Unrealized Gains |  |  | 77
Gross Unrealized Losses |  |  |
Fair Value |  |  | 5,430
Corporate bonds [Member] |  |  |
Available-for-sale securities: |  |  |
Amortized Cost |  |  | 4,643
Gross Unrealized Gains |  |  |
Gross Unrealized Losses |  |  |
Fair Value |  |  | 4,643
Equity [Member] |  |  |
Available-for-sale securities: |  |  |
Amortized Cost |  | 78 | 74
Gross Unrealized Gains |  | 27 |
Gross Unrealized Losses |  |  | (26)
Fair Value |  | 105 | 48
U.S. Treasury notes [Member] |  |  |
Available-for-sale securities: |  |  |
Amortized Cost |  | 1,690 | 6,673
Gross Unrealized Gains |  |  |
Gross Unrealized Losses |  | (1) |
Fair Value |  | 1,689 | 6,673
Municipal bonds [Member] |  |  |
Available-for-sale securities: |  |  |
Amortized Cost |  | 3,132 | 8,201
Gross Unrealized Gains |  |  | 4
Gross Unrealized Losses |  | (5) | (1)
Fair Value |  | $ 3,127 | $ 8,204
[1] | Each of the Company's certificates of deposit has a CUSIP, was purchased in the secondary market through a broker, and may be sold in the secondary market.

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