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Marketable Securities - Amortized Cost and Estimated Fair Value of Cash Equivalents and Marketable Securities by Contractual Maturity (Details) (USD $)
Apr. 30, 2015
Jan. 31, 2015
Investments Debt And Equity Securities [Abstract]    
Amortized Cost, Less than one year $ 112,196,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost  
Amortized Cost, Due in one to five years 13,485,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost  
Amortized Cost 125,681,000us-gaap_AvailableForSaleSecuritiesAmortizedCost  
Estimated Fair Value, Less than one year 112,200,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue  
Estimated Fair Value, Due in one to five years 13,484,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue  
Estimated Fair Value, Total $ 125,684,000us-gaap_AvailableForSaleSecurities $ 0us-gaap_AvailableForSaleSecurities