Stock-Based Compensation - Expenses (Details) - USD ($)	3 Months Ended			6 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Oct. 31, 2018	Jan. 31, 2020	Jan. 31, 2019	Oct. 31, 2019	Jul. 31, 2019
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 1,238,000	$ 1,191,000	$ 1,191,000	$ 2,117,000	$ 2,237,000
Estimated income tax benefit	(271,000)		(260,000)	(460,000)	(488,000)
Net stock-based compensation expense	967,000		931,000	1,657,000	1,749,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	10,792,000			10,792,000
Estimated forfeitures related to unvested stock-based awards	955,000			$ 955,000
Weighted average number of years net compensation cost is expected to be recognized over				3 years 1 month 5 days
Stock-based compensation capitalized and included in ending inventory	48,000			$ 48,000			$ 48,000
Stock Options
Stock-based Compensation Expenses
Total intrinsic value of stock-based awards settled	1,559,000	$ 0		1,864,000	561,000
Stock-based compensation expense before income tax benefit	$ 82,000		181,000	$ 164,000	352,000
Number of stock-based option awards outstanding at period end (in shares)	1,269,865			1,269,865		1,503,295	1,555,555
Performance Shares
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 421,000		386,000	$ 773,000	792,000
RSUs and restricted stock
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	60,000		56,000	117,000	108,000
ESPP
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	675,000		568,000	1,373,000	1,115,000
Share units
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 0		0	$ (310,000)	(130,000)
Stock Appreciation Rights (SARs)
Stock-based Compensation Expenses
Number of stock-based option awards outstanding at period end (in shares)	0			0			0
Cost of sales
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 60,000		60,000	$ 119,000	118,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	1,094,000		1,051,000	1,837,000	1,956,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 84,000		$ 80,000	$ 161,000	$ 163,000
2001 Employee Stock Purchase Plan | ESPP
Stock-based Compensation Expenses
Discount offered to employees participating in the ESPP as a percentage of market price	15.00%		15.00%	15.00%	15.00%