Stock-Based Compensation - Expenses (Details) - USD ($)	3 Months Ended		9 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2017	Apr. 30, 2016	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 991,000	$ 1,041,000	$ 2,980,000	$ 3,166,000
Estimated income tax benefit	(349,000)	(391,000)	(1,051,000)	(1,103,000)
Net stock-based compensation expense	642,000	650,000	1,929,000	2,063,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	7,756,000		7,756,000
Estimated forfeitures related to unvested stock-based awards	705,000		$ 705,000
Weighted average number of years net compensation cost is expected to be recognized over			2 years 10 months 24 days
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	$ 368,000	591,000	$ 1,000,000	1,803,000
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)	1,900,975		1,900,975		1,910,576	2,138,174	2,256,679
Performance Shares
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 361,000	369,000	$ 1,227,000	1,093,000
Employee Stock Purchase Plan - ESPP
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	41,000	35,000	120,000	118,000
RSUs and restricted stock
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 221,000	46,000	$ 633,000	152,000
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	$ 56,000	70,000	$ 162,000	233,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	862,000	875,000	2,591,000	2,630,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 73,000	$ 96,000	$ 227,000	$ 303,000
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%