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Short-Term Investments - Summary of Estimated Fair Value of Short-Term Investments, Designated as Available-for-Sale and Classified by Contractual Maturity (Detail) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2015
Jan. 31, 2014
Investments Debt And Equity Securities [Abstract]    
Due in one year or less $ 224,263us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue $ 17,667us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue
Due in greater than one year 44,357us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue 7,958us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue
Available-for-sale securities, Estimated Fair Value $ 268,620us-gaap_AvailableForSaleSecuritiesCurrent $ 25,625us-gaap_AvailableForSaleSecuritiesCurrent