Stock-Based Compensation - Expenses (Details) - USD ($)		3 Months Ended		9 Months Ended
	Apr. 30, 2018	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2018	Apr. 30, 2017	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 1,104,000	$ 991,000	$ 2,931,000	$ 2,980,000
Estimated income tax benefit		(240,000)	(349,000)	(734,000)	(1,051,000)
Net stock-based compensation expense		864,000	642,000	2,197,000	1,929,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	$ 8,088,000	8,088,000		8,088,000
Estimated forfeitures related to unvested stock-based awards	$ 801,000	801,000		801,000
Weighted average number of years net compensation cost is expected to be recognized over	2 years 10 months 10 days
Stock-based compensation capitalized and included in ending inventory	$ 12,000	12,000		12,000				$ 12,000
Stock Options
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 309,000	368,000	$ 845,000	1,000,000
Number of stock-based option awards outstanding at period end (in shares)	1,734,775	1,734,775		1,734,775		1,805,485	1,814,835	1,855,875
Performance Shares
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 363,000	361,000	$ 846,000	1,227,000
RSUs and restricted stock
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		376,000	221,000	1,150,000	633,000
ESPP
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		56,000	41,000	152,000	120,000
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				0
Cost of sales
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 55,000	56,000	$ 146,000	162,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		976,000	862,000	2,584,000	2,591,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense before income tax benefit		$ 73,000	$ 73,000	$ 201,000	$ 227,000
2001 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%	15.00%	15.00%