Stock-Based Compensation - Expenses (Details) - USD ($)	3 Months Ended		9 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2020	Apr. 30, 2019	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 981,000	$ 1,119,000	$ 3,098,000	$ 3,356,000
Estimated income tax benefit	(204,000)	(244,000)	(664,000)	(732,000)
Net stock-based compensation expense	777,000	875,000	2,434,000	2,624,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	9,153,000		9,153,000
Estimated forfeitures related to unvested stock-based awards	1,065,000		$ 1,065,000
Weighted average number of years net compensation cost is expected to be recognized over			2 years 11 months 14 days
Stock-based compensation capitalized and included in ending inventory	48,000		$ 48,000				$ 48,000
Cost of sales
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	45,000	52,000	164,000	170,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	878,000	1,004,000	2,715,000	2,960,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 58,000	63,000	$ 219,000	226,000
Stock Appreciation Rights (SARs) [Member]
Stock-based Compensation Expenses
Number of stock-based option awards outstanding at period end (in shares)	0		0				0
Stock options
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 39,000	174,000	$ 203,000	526,000
Number of stock-based option awards outstanding at period end (in shares)	1,139,675		1,139,675		1,269,865	1,503,295	1,555,555
Performance Shares
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 412,000	374,000	$ 1,185,000	1,166,000
RSUs and restricted stock
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	477,000	515,000	1,850,000	1,630,000
ESPP
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	53,000	56,000	$ 170,000	164,000
ESPP | 2001 Employee Stock Purchase Plan
Stock-based Compensation Expenses
Discount offered to employees participating in the ESPP as a percentage of market price			15.00%
Share units
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 0	$ 0	$ (310,000)	$ (130,000)