Stock-Based Compensation - Expenses (Details) (USD $)	3 Months Ended		9 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2015	Apr. 30, 2014	Jul. 31, 2014
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 1,244,000	$ 1,070,000	$ 3,642,000	$ 3,086,000
Estimated income tax benefit	(432,000)	(394,000)	(1,283,000)	(1,143,000)
Net stock-based compensation expense	812,000	676,000	2,359,000	1,943,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	8,786,000		8,786,000
Estimated forfeitures related to unvested stock-based awards	608,000		608,000
Weighted average number of years net compensation cost is expected to be recognized over			3 years 0 months 0 days
Stock-based compensation capitalized and included in ending inventory	68,000		68,000		68,000
Stock Options
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	778,000	668,000	2,267,000	2,035,000
Performance Shares
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	308,000	264,000	883,000	671,000
Employee Stock Purchase Plan - ESPP
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	52,000	47,000	158,000	135,000
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	106,000	67,000	306,000	203,000
Share units
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	0	15,000	28,000	27,000
Total equity-classified stock-based awards
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	1,244,000	1,061,000	3,642,000	3,071,000
SARs
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	0	9,000	0	15,000
Cost of sales
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	71,000	57,000	204,000	194,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	1,005,000	860,000	2,963,000	2,463,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit	$ 168,000	$ 153,000	$ 475,000	$ 429,000