Stock-Based Compensation (Details) (USD $)	3 Months Ended		9 Months Ended
	Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2011	Apr. 30, 2010	Jul. 31, 2010
Stock-based compensation expense before income tax benefit	$ 1,118,000	$ 2,332,000	$ 3,977,000	$ 5,758,000
Income tax benefit	(399,000)	(839,000)	(1,430,000)	(2,134,000)
Net stock-based compensation expense	719,000	1,493,000	2,547,000	3,624,000
Total stock-based compensation expense related to employee stock purchase plan	60,000	72,000	208,000	235,000
Required fair value remeasurement of liability-classified stock appreciation rights	(2,000)	(19,000)	8,000	(13,000)
Stock-based compensation capitalized and included in ending inventory	117,000		117,000		159,000
Per share weighted average grant date fair value of stock based awards granted	$ 7.28		$ 7.24	$ 9.32
Expected dividend yield	3.59%		3.59%	0.00%
Expected volatility	38.00%		38.00%	38.00%
Risk free interest rate	2.30%		2.24%	1.33%
Expected life (in years)	5.28		5.27	3.50
Contractual term on stock-based awards granted			five or ten years
Vesting period on stock-based awards granted			three or five years
Share-based compensation arrangement by share-based payment award, plan modification, incremental compensation cost		494,000		494,000
Number of previously granted stock based awards modified		222,500		222,500
Expected life (in years) on modified stock-based awards		0.88		0.88
Expected volatility on modified stock-based awards		32.93%		32.93%
Risk free interest rate on modified stock-based awards		0.33%		0.33%
Expected dividend yield on modified stock-based awards		0.00%		0.00%
Accrued expense related to the cash settlement of liability-classified stock appreciation rights	82,000		82,000		74,000
Targeted annual dividend per share	$ 1.00		$ 1.00
Actual income tax benefit recorded for the tax deductions relating to the exercise of stock based awards			291,000	472,000
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			(137,000)	(213,000)
Excess income tax benefit recorded as an increase to additional paid-in capital			154,000	259,000
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			0	(7,000)
Excess income tax benefit from exercised equity-classified stock- based awards reported as cash flow from financing activities			154,000	252,000
Total remaining unrecognized compensation cost related to the unvested stock-based awards	7,261,000		7,261,000
Estimated forfeitures related to total unrecognized stock-based compensation cost	861,000		861,000
Net compensation cost expected to be recognized over a weighted average number of years			3.0
Hypothetical tax benefits related to stock-based awards	24,350,000		24,350,000
Reduction to APIC due to reversal of deferred tax assets associated with expired and unexercised stock-based awards	523,000		1,760,000
Number of stock-based awards authorized for issuance, subsequent event			648,750
Total unrecognized stock-based compensation, net of estimated forfeitures, related to stock-based awards authorized for issuance, subsequent event			4,000,000
Number of stock-based awards authorized for issuance with a contractual term of five years and a vesting period of three years, subsequent event			75,000
Cost of Sales [Member]
Stock-based compensation expense before income tax benefit	88,000	159,000	361,000	466,000
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense before income tax benefit	824,000	1,827,000	2,875,000	4,301,000
Research and Development Expenses [Member]
Stock-based compensation expense before income tax benefit	$ 206,000	$ 346,000	$ 741,000	$ 991,000