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Fair Value - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 3 Months Ended
Jan. 31, 2014
Jan. 31, 2013
Apr. 30, 2013
Auction Rate Securities
Jan. 31, 2013
Auction Rate Securities
Jan. 31, 2013
Fair Value, Inputs, Level 3
Apr. 30, 2013
Fair Value, Inputs, Level 3
Auction Rate Securities
Jan. 31, 2013
Fair Value, Inputs, Level 3
Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Proceeds from sale of available-for-sale securities     $ 4,580     $ 4,580  
Amortized cost of available-for-sale securities 647,483 378,393         4,925
Estimated fair value of available-for-sale securities $ 648,235 $ 378,071   $ 4,330 $ 4,330   $ 4,330