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Marketable Debt Securities (Details 1) (USD $)
Oct. 31, 2011
Oct. 31, 2010
Legal maturities of debt investments    
Amortized Cost, Less than one year $ 0  
Amortized Cost, Due in 1-2 years 49,933,000  
Amortized Cost, Total 49,933,000  
Estimated Fair Value, Less than one year 0  
Estimated Fair Value, Due in 1-2 years 50,264,000  
Estimated Fair Value $ 50,264,000 $ 0