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Fair Value - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Apr. 30, 2014
Jan. 31, 2014
Apr. 30, 2013
Apr. 30, 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
Amortized cost of available-for-sale securities 325,082 647,483 364,396 4,925
Estimated fair value of available-for-sale securities $ 325,490 $ 648,235 $ 364,709 $ 4,330