Stock-Based Compensation - Expenses (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2016	Jan. 31, 2015	Jul. 31, 2015
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 1,074,000	$ 1,061,000	$ 2,125,000	$ 2,398,000
Estimated income tax benefit	(347,000)	(383,000)	(712,000)	(851,000)
Net stock-based compensation expense	727,000	678,000	1,413,000	1,547,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	8,686,000		8,686,000
Estimated forfeitures related to unvested stock-based awards	803,000		$ 803,000
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		$ 92,000
Stock Options
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	609,000	731,000	1,212,000	1,489,000
Performance Shares
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	390,000	167,000	724,000	575,000
Employee Stock Purchase Plan - ESPP
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	40,000	53,000	$ 83,000	$ 106,000
Discount offered to employees participating in the ESPP as a percentage of market price			15.00%	15.00%
RSUs and restricted stock
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	35,000	96,000	$ 106,000	$ 200,000
Share units
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	0	14,000	0	28,000
Cost of sales
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	100,000	66,000	163,000	133,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	881,000	856,000	1,755,000	1,958,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 93,000	$ 139,000	$ 207,000	$ 307,000