Income Taxes (Tax Effects of Temporary Differences) (Details) - USD ($)	Jul. 31, 2018	Jul. 31, 2017
Deferred tax assets:
Inventory and warranty reserves	$ 5,089,000	$ 7,854,000
Compensation and commissions	3,511,000	3,807,000
Federal, state and foreign research and experimentation credits	18,816,000	16,286,000
Federal alternative minimum tax credit	3,243,000	2,652,000
Stock-based compensation	5,092,000	7,767,000
Acquisition-related contingent liabilities	2,477,000	4,687,000
Federal and state net operating losses	7,349,000	19,880,000
Other	4,672,000	8,764,000
Less valuation allowance	(11,854,000)	(8,633,000)
Total deferred tax assets	38,395,000	63,064,000
Deferred tax liabilities:
Plant and equipment	(1,155,000)	(1,309,000)
Intangibles	(48,167,000)	(79,061,000)
Total deferred tax liabilities	(49,322,000)	(80,370,000)
Net deferred tax liabilities	$ (10,927,000)	$ (17,306,000)