Fair Value Measurements and Financial Instruments (Details) (USD $)			6 Months Ended
	Jan. 31, 2013	Jul. 31, 2012	Jan. 31, 2013 Acquisition of Stampede Technologies, Inc. [Member]
Debt instrument fair value	$ 206,460,000	$ 211,920,000
Amount invested in money market mutual funds disclosed at fair value	58,160,000	84,610,000
Business acquisition, name of acquired entity			Stampede Technologies, Inc.
Business acquisition, contingent consideration, at fair value	$ 375,000	$ 3,519,000	$ 375,000