Stock-Based Compensation - Expenses (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016	Oct. 31, 2016	Jul. 31, 2016
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 1,019,000	$ 1,074,000	$ 1,989,000	$ 2,125,000
Estimated income tax benefit	(361,000)	(347,000)	(702,000)	(712,000)
Net stock-based compensation expense	658,000	727,000	1,287,000	1,413,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	8,741,000		8,741,000
Estimated forfeitures related to unvested stock-based awards	771,000		$ 771,000
Weighted average number of years net compensation cost is expected to be recognized over			3 years
Stock-based compensation capitalized and included in ending inventory	51,000		$ 51,000			$ 51,000
Stock Options
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 386,000	609,000	$ 632,000	1,212,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross			0
Number of stock-based option awards outstanding at period end (in shares)	1,910,576		1,910,576		2,138,174	2,256,679
Performance Shares
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 372,000	390,000	$ 866,000	724,000
Employee Stock Purchase Plan - ESPP
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	37,000	40,000	79,000	83,000
RSUs and restricted stock
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 224,000	35,000	$ 412,000	106,000
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	$ 58,000	100,000	$ 106,000	163,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	878,000	881,000	1,729,000	1,755,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 83,000	$ 93,000	$ 154,000	$ 207,000
2001 Employee Stock Purchase Plan | 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%