Stock-Based Compensation - Expenses (Details) - USD ($)		3 Months Ended
	Oct. 31, 2017	Oct. 31, 2017	Oct. 31, 2016	Jul. 31, 2017
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 747,000	$ 970,000
Estimated income tax benefit		(260,000)	(341,000)
Net stock-based compensation expense		487,000	629,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	$ 10,222,000	10,222,000
Estimated forfeitures related to unvested stock-based awards	$ 812,000	812,000
Weighted average number of years net compensation cost is expected to be recognized over	3 years 2 months 4 days
Stock-based compensation capitalized and included in ending inventory	$ 12,000	12,000		$ 12,000
Stock Options
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 267,000	246,000
Number of stock-based option awards outstanding at period end (in shares)	1,814,835	1,814,835		1,855,875
Performance Shares
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 112,000	494,000
RSUs and restricted stock
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		385,000	188,000
Employee Stock Purchase Plan - ESPP
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		45,000	42,000
Share units
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ (62,000)	0
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		$ 40,000	48,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		654,000	851,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 53,000	$ 71,000
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%