Fair Value Measurements and Financial Instruments (Details) (USD $)			3 Months Ended
	Oct. 31, 2012	Jul. 31, 2012	Oct. 31, 2012 Acquisition of Stampede Technologies, Inc. [Member]
Debt instrument fair value	$ 205,500,000	$ 211,920,000
Amount invested in money market mutual funds disclosed at fair value	80,138,000	84,610,000
Name of acquired entity			Stampede Technologies, Inc.
Business acquisition, contingent consideration, at fair value	$ 1,248,000	$ 3,519,000	$ 1,248,000