Cash, Cash Equivalents and Marketable Securities (Details) (USD $) In Thousands	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2009	Jul. 31, 2008
Cash and Cash Equivalents and Marketable Securities [Line Items]
Cost	$ 74,009	$ 268,188	$ 162,691	$ 38,954
Unrealized Gains
Unrealized Losses Less Than 12 Months
Unrealized Losses 12 Months or Longer
Estimated Fair Value	74,009	268,188
Cash
Cash and Cash Equivalents and Marketable Securities [Line Items]
Cost	42,664	131,070
Unrealized Gains
Unrealized Losses Less Than 12 Months
Unrealized Losses 12 Months or Longer
Estimated Fair Value	42,664	131,070
Money Market Funds
Cash and Cash Equivalents and Marketable Securities [Line Items]
Cost	31,345	107,118
Unrealized Gains
Unrealized Losses Less Than 12 Months
Unrealized Losses 12 Months or Longer
Estimated Fair Value	31,345	107,118
Cash Equivalents-Us Treasury Bills
Cash and Cash Equivalents and Marketable Securities [Line Items]
Cost		30,000
Unrealized Gains
Unrealized Losses Less Than 12 Months
Unrealized Losses 12 Months or Longer
Estimated Fair Value		$ 30,000