Income Taxes (Provision for Income Taxes Differed from Amounts Computed by the U.S. Federal Income Tax Rate) (Details) (USD $)	12 Months Ended
	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2009
Income Taxes [Abstract]
Computed expected tax expense	$ 35,632,000	$ 34,056,000	$ 25,644,000
Computed expected tax rate	35.00%	35.00%	35.00%
State and local income taxes, net of Federal benefit	2,614,000	3,118,000	871,000
State and local income taxes, net of Federal benefit effective tax rate	2.60%	3.20%	1.20%
Impairment of Goodwill	0	1,666,000	0
Impairment of Goodwill, effective tax rate	0.00%	1.70%	0.00%
In-process research & development	0	0	2,170,000
In-process research & development, effective tax rate	0.00%	0.00%	3.00%
Nondeductible stock-based compensation	94,000	167,000	419,000
Nondeductible stock-based compensation, effective tax rate	0.10%	0.20%	0.60%
Domestic production activities deduction	(2,873,000)	(2,086,000)	(1,117,000)
Domestic production activities deduction, effective tax rate	(2.80%)	(2.20%)	(1.50%)
Research and experimentation credits	(1,255,000)	(137,000)	(2,351,000)
Research and experimentation credits, effective tax rate	(1.30%)	(0.10%)	(3.20%)
Change in the beginning of the year valuation allowance for deferred tax assets	0	(50,000)	(50,000)
Change in the beginning of the year valuation allowance for deferred tax assets, effective tax rate	0.00%	(0.10%)	(0.10%)
Foreign income taxes	151,000	9,000	(49,000)
Foreign income taxes, effective tax rate	0.20%	0.10%	(0.10%)
Other	(454,000)	(71,000)	207,000
Other, effective tax rate	(0.50%)	(0.10%)	0.20%
Total provision for income taxes	$ 33,909,000	$ 36,672,000	$ 25,744,000
Income Tax effective tax rate, Continuing Operations	33.30%	37.70%	35.10%