Stock-Based Compensation (Details) (USD $)	3 Months Ended		9 Months Ended
	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2012	Apr. 30, 2011	Jul. 31, 2011
Stock-based compensation expense before income tax benefit	$ 809,000	$ 1,118,000	$ 2,718,000	$ 3,977,000
Income tax benefit	(308,000)	(399,000)	(1,009,000)	(1,430,000)
Net stock-based compensation expense	501,000	719,000	1,709,000	2,547,000
Total stock-based compensation expense related to employee stock purchase plan	56,000	60,000	176,000	208,000
Required fair value remeasurement of liability-classified stock appreciation rights	(9,000)	(2,000)	(3,000)	8,000
Stock-based compensation capitalized and included in ending inventory	48,000		48,000		117,000
Per share weighted average grant date fair value of stock based awards granted	$ 7.19	$ 7.28	$ 5.99	$ 7.24
Expected dividend yield	3.49%	3.59%	3.97%	3.59%
Expected volatility	36.00%	38.00%	36.19%	38.00%
Risk-free interest rate	0.85%	2.30%	0.83%	2.24%
Expected life (in years)	5 years 2 months 9 days	5 years 3 months 11 days	5 years 2 months 23 days	5 years 3 months 7 days
Accrued expense related to the cash settlement of liability-classified stock appreciation rights	19,000		19,000		22,000
Targeted annual dividend per share			$ 1.10	$ 1.00
Stock units issued during period, number of shares	194		194
Stock units issued during period, weighted average grant date fair value	$ 32.27		$ 32.27
Actual income tax benefit recorded for the tax deductions relating to the exercise of stock-based awards			341,000	291,000
Less: Tax benefit initially recognized on exercised stock-based awards vesting subsequent to the adoption of accounting standards that require us to expense stock-based awards, excluding income tax shortfalls			(197,000)	(137,000)
Excess income tax benefit recorded as an increase to additional paid-in capital			144,000	154,000
Less: Tax benefit initially disclosed but not previously recognized on exercised equity-classified stock-based awards vesting prior to the adoption of accounting standards that require us to expense stock-based awards			(2,000)	0
Excess income tax benefit from stock-based award exercises			142,000	154,000
Adjustments to Additional Paid in Capital, Income Tax Deficiency from Share-based Compensation			192,000	0
Total remaining unrecognized compensation cost related to the unvested stock-based awards	6,695,000		6,695,000
Estimated forfeitures related to unvested stock-based awards	545,000		545,000
Weighted average number of years net compensation cost is expected to be recognized over			3 years 4 months 24 days
Hypothetical tax benefits related to stock-based awards	22,739,000		22,739,000
Reduction to APIC due to reversal of unrealized deferred tax assets associated with certain vested equity-classified expired and unexercised stock-based awards			1,329,000	1,760,000
Cost of Sales [Member]
Stock-based compensation expense before income tax benefit	46,000	88,000	224,000	361,000
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense before income tax benefit	626,000	824,000	2,066,000	2,875,000
Research and Development Expense [Member]
Stock-based compensation expense before income tax benefit	137,000	206,000	428,000	741,000
Subsequent Event [Member]
Number of stock-based awards authorized for issuance, subsequent event			412,946
Number of stock options authorized for issuance, subsequent event.			365,275
Number of performance shares authorized for issuance, subsequent event.			35,003
Number of restricted stock units authorized for issuance, subsequent event.			12,668
Total unrecognized stock-based compensation, net of estimated forfeitures, related to stock-based awards authorized for issuance, subsequent event			$ 3,508,000
Share-Based Award Granted With Five Year Contractual Term [Member]
Vesting period of stock-based awards granted			3 years
Contractual term (in years)			5 years
Share-Based Award Granted With Ten Year Contractual Term [Member]
Vesting period of stock-based awards granted			5 years
Contractual term (in years)			10 years