Fair Value Measurements (Details) - USD ($) $ in Thousands	Jul. 31, 2017	Jul. 31, 2016
Available-for-sale securities:
Marketable securities	$ 58,272	$ 52,949
Rafael convertible promissory notes	6,300	2,000
Total	64,572	54,949
Fair Value Measurements, Recurring basis [Member] | Level 1 [Member]
Available-for-sale securities:
Marketable securities	12,151	12,445
Rafael convertible promissory notes
Total	12,151	12,445
Fair Value Measurements, Recurring basis [Member] | Level 2 [Member]
Available-for-sale securities:
Marketable securities	46,121	40,504
Rafael convertible promissory notes
Total	46,121	40,504
Fair Value Measurements, Recurring basis [Member] | Level 3 [Member]
Available-for-sale securities:
Marketable securities
Rafael convertible promissory notes	6,300	2,000
Total	$ 6,300	$ 2,000