Market Value and Amortized Cost of Marketable Securities (Detail) - USD ($) $ in Thousands		Apr. 30, 2018	Jul. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Market Value		$ 51,292	$ 57,087
Amortized Cost		51,429	56,918
Corporate
Schedule of Available-for-sale Securities [Line Items]
Market Value	[1]	27,461	24,969
Amortized Cost	[1]	27,490	24,828
Government
Schedule of Available-for-sale Securities [Line Items]
Market Value		7,039	12,408
Amortized Cost		7,047	12,410
Collateralized Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Market Value		2,435	2,335
Amortized Cost		2,450	2,332
Asset-backed Securities
Schedule of Available-for-sale Securities [Line Items]
Market Value		14,357	17,375
Amortized Cost		$ 14,442	$ 17,348

[1] There are no held to maturity investments included in the above figures as of April 30, 2018 or July 31, 2017