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Investments And Fair Value Measurements (Financial Assets Measured At Fair Value On A Recurring Basis) (Details) (USD $)
In Thousands
Jul. 31, 2011
Jul. 31, 2010
Cash and Cash Equivalents $ 215,435 $ 247,751
Auction Rate Securities [Member]
   
Auction Rate Securities 2,042  
Level 1 [Member] | Auction Rate Securities [Member]
   
Auction Rate Securities 0  
Level 2 [Member] | Auction Rate Securities [Member]
   
Auction Rate Securities 0  
Level 3 [Member] | Auction Rate Securities [Member]
   
Auction Rate Securities 2,042  
Auction Rate Securities And Put Rights [Member]
   
Auction Rate Securities   5,327
Auction Rate Securities And Put Rights [Member] | Level 1 [Member]
   
Auction Rate Securities   0
Auction Rate Securities And Put Rights [Member] | Level 2 [Member]
   
Auction Rate Securities   0
Auction Rate Securities And Put Rights [Member] | Level 3 [Member]
   
Auction Rate Securities   5,327
Level 1 [Member]
   
Cash and Cash Equivalents 215,435 247,751
Level 2 [Member]
   
Cash and Cash Equivalents 0 0
Level 3 [Member]
   
Cash and Cash Equivalents $ 0 $ 0