Short-Term Investments (Details 1) (USD $) In Thousands	Jul. 31, 2011	Jul. 31, 2010
Cost Basis and Fair Value of Debt Securities by Contractual Maturity
One year or less, Cost basis	$ 60,255	$ 93,597
One to two years, Cost basis	92,715	30,378
Total short-term investments, Cost basis	152,970	123,975
One year or less, Fair value	60,358	93,700
One to two years, Fair value	92,827	30,467
Total short-term investments, Fair value	$ 153,185	$ 124,167