Stock-Based Compensation (Expenses) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2021	Jan. 31, 2020	Oct. 31, 2020	Jul. 31, 2020
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 1,287,000	$ 1,238,000	$ 1,986,000	$ 2,117,000
Estimated Income tax benefit	(280,000)	(271,000)	(424,000)	(460,000)
Net stock-based compensation expense	1,007,000	967,000	1,562,000	1,657,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	12,736,000		12,736,000
Estimated forfeitures related to unvested stock-based awards	1,103,000		$ 1,103,000
Weighted average number of years net compensation cost is expected to be recognized over			3 years 3 months 18 days
Stock-based compensation capitalized and included in ending inventory	48,000		$ 48,000			$ 48,000
Stock options
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 97,000	82,000	$ 217,000	164,000
Number of stock-based awards outstanding at period end (in shares)	1,331,835		1,331,835		1,344,635	1,422,025
Performance shares
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 443,000	421,000	$ 665,000	773,000
RSUs and restricted stock
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	699,000	675,000	1,621,000	1,373,000
ESPP
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	48,000	60,000	$ 99,000	117,000
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 (benefit) before income tax benefit	$ 0	0	$ (616,000)	(310,000)
2000 Stock Incentive Plan | Stock options
Stock-based Compensation Expenses
Number of stock-based awards outstanding at period end (in shares)	1,331,835		1,331,835
2000 Stock Incentive Plan | Stock appreciation rights (SARs)
Stock-based Compensation Expenses
Number of stock-based awards outstanding at period end (in shares)	0		0			0
Cost of sales
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 59,000	60,000	$ 132,000	119,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	1,158,000	1,094,000	1,700,000	1,837,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 70,000	$ 84,000	$ 154,000	$ 161,000