Stock-Based Compensation - Expenses (Details) - USD ($)		3 Months Ended		6 Months Ended
	Oct. 31, 2017	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017	Jul. 31, 2017
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 1,080,000	$ 1,019,000	$ 1,827,000	$ 1,989,000
Estimated income tax benefit		(234,000)	(361,000)	(494,000)	(702,000)
Net stock-based compensation expense		846,000	658,000	1,333,000	1,287,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards		9,015,000		9,015,000
Estimated forfeitures related to unvested stock-based awards		902,000		902,000
Weighted average number of years net compensation cost is expected to be recognized over	2 years 11 months 26 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		$ 268,000	386,000	$ 536,000	632,000
Number of stock-based option awards outstanding at period end (in shares)	1,814,835	1,805,485		1,805,485		1,855,875
Performance Shares
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 371,000	372,000	$ 483,000	866,000
RSUs and restricted stock
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		390,000	224,000	774,000	412,000
Employee Stock Purchase Plan - ESPP
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		51,000	37,000	96,000	79,000
Share units
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 0	0	$ (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		$ 51,000	58,000	$ 91,000	106,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		954,000	878,000	1,608,000	1,729,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 75,000	$ 83,000	$ 128,000	$ 154,000
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%