(Stock-Based Compensation Expenses) (Details) - USD ($)	12 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 11,427,000	$ 8,569,000	$ 8,506,000
Estimated Income tax benefit	(2,553,000)	(2,005,000)	(3,065,000)
Net stock-based compensation expense	8,874,000	6,564,000	5,441,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	7,714,000
Estimated forfeitures related to unvested stock-based awards	$ 869,000
Weighted average number of years net compensation cost is expected to be recognized over	2 years 9 months 18 days
Stock-based compensation capitalized and included in ending inventory		48,000
Stock options
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 739,000	$ 1,089,000	$ 1,400,000
Number of stock-based awards outstanding at period end (in shares)	1,555,555	1,668,975	1,855,875	2,256,679
Performance Shares
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 1,554,000	$ 1,013,000	$ 1,607,000
RSUs and restricted stock
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	2,149,000	1,458,000	829,000
Employee Stock Purchase Plan
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 215,000	205,000	162,000
Discount offered to employees participating in the ESPP as a percentage of market price	15.00%
Share units
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 6,770,000	4,804,000	4,508,000
Recoupment of share units
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ (130,000)	$ (62,000)
2000 Stock Incentive Plan | Stock options
Stock-based Compensation Expenses
Number of stock-based awards outstanding at period end (in shares)	1,555,555
2000 Stock Incentive Plan | Stock appreciation rights (SARs)
Stock-based Compensation Expenses
Number of stock-based awards outstanding at period end (in shares)	0	0
Cost of sales
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 1,047,000	$ 758,000	760,000
Selling, general and administrative expenses
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	9,336,000	6,866,000	7,071,000
Research and development expenses
Stock-based Compensation Expenses
Stock-based compensation expense (benefit) before income tax benefit	$ 1,044,000	$ 945,000	$ 675,000