Stock-Based Compensation (Details) (USD $)	3 Months Ended		6 Months Ended
	Jan. 31, 2012 years	Jan. 31, 2011	Jan. 31, 2012 years	Jan. 31, 2011 years	Jul. 31, 2011
Stock-based compensation expense before income tax benefit	$ 1,036,000	$ 1,351,000	$ 1,909,000	$ 2,859,000
Income tax benefit	(394,000)	(489,000)	(701,000)	(1,031,000)
Net stock-based compensation expense	642,000	862,000	1,208,000	1,828,000
Total stock-based compensation expense related to employee stock purchase plan	59,000	79,000	120,000	148,000
Required fair value remeasurement of liability-classified stock appreciation rights	(14,000)	(7,000)	6,000	10,000
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	$ 6.34	$ 0.00	$ 5.93	$ 6.67
Expected dividend yield	3.68%		4.00%	3.66%
Expected volatility	37.70%		36.20%	38.00%
Risk-free interest rate	0.42%		0.83%	1.27%
Expected life (in years)	3.81		5.24	5.18
Contractual term on stock-based awards granted			five or ten years
Vesting period on stock-based awards granted			three or five years
Accrued expense related to the cash settlement of liability-classified stock appreciation rights	28,000		28,000		22,000
Targeted annual dividend per share			$ 1.10	$ 1.00
Actual income tax benefit recorded for the tax deductions relating to the exercise of stock-based awards			235,000	215,000
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			(151,000)	(102,000)
Excess income tax benefit recorded as an increase to additional paid-in capital			84,000	113,000
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			82,000	113,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	7,527,000		7,527,000
Estimated forfeitures related to unvested stock-based awards	587,000		587,000
Weighted average number of years net compensation cost is expected to be recognized over			3.5
Hypothetical tax benefits related to stock-based awards	22,851,000		22,851,000
Reduction to APIC due to reversal of unrealized deferred tax assets associated with certain vested equity-classified expired and unexercised stock-based awards			1,186,000	1,237,000
Cost of Sales [Member]
Stock-based compensation expense before income tax benefit	125,000	151,000	178,000	273,000
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense before income tax benefit	795,000	953,000	1,440,000	2,051,000
Research and Development Expenses [Member]
Stock-based compensation expense before income tax benefit	$ 116,000	$ 247,000	$ 291,000	$ 535,000