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Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Details) (USD $)
Apr. 30, 2015
Jan. 31, 2015
Schedule Of Available For Sale Securities [Line Items]    
Amortized Cost $ 125,681,000us-gaap_AvailableForSaleSecuritiesAmortizedCost  
Unrealized Gain 16,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax  
Unrealized Loss (13,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax  
Marketable securities 125,684,000us-gaap_AvailableForSaleSecurities 0us-gaap_AvailableForSaleSecurities
Corporate Paper    
Schedule Of Available For Sale Securities [Line Items]    
Amortized Cost 62,496,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember
 
Unrealized Gain 10,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember
 
Unrealized Loss (1,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember
 
Marketable securities 62,505,000us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CommercialPaperMember
 
U.S. Government Agency Obligations    
Schedule Of Available For Sale Securities [Line Items]    
Amortized Cost 20,295,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
 
Unrealized Gain 1,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
 
Unrealized Loss (1,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
 
Marketable securities 20,295,000us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
 
Corporate Debt Securities    
Schedule Of Available For Sale Securities [Line Items]    
Amortized Cost 15,518,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
 
Unrealized Gain 4,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
 
Unrealized Loss (7,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
 
Marketable securities 15,515,000us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
 
Asset-backed Securities    
Schedule Of Available For Sale Securities [Line Items]    
Amortized Cost 15,335,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_AssetBackedSecuritiesMember
 
Unrealized Gain 1,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_AssetBackedSecuritiesMember
 
Unrealized Loss (2,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_AssetBackedSecuritiesMember
 
Marketable securities 15,334,000us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_AssetBackedSecuritiesMember
 
U.S. Government Obligations    
Schedule Of Available For Sale Securities [Line Items]    
Amortized Cost 12,037,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasurySecuritiesMember
 
Unrealized Loss (2,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasurySecuritiesMember
 
Marketable securities 12,035,000us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_USTreasurySecuritiesMember
 
Included in Cash and Cash Equivalents    
Schedule Of Available For Sale Securities [Line Items]    
Amortized Cost 21,692,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_CashAndCashEquivalentsMember
 
Unrealized Gain 3,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_CashAndCashEquivalentsMember
 
Marketable securities 21,695,000us-gaap_AvailableForSaleSecurities
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_CashAndCashEquivalentsMember
 
Included in Marketable Investments    
Schedule Of Available For Sale Securities [Line Items]    
Amortized Cost 103,989,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_AvailableforsaleSecuritiesMember
 
Unrealized Gain 13,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_AvailableforsaleSecuritiesMember
 
Unrealized Loss (13,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_AvailableforsaleSecuritiesMember
 
Marketable securities $ 103,989,000us-gaap_AvailableForSaleSecurities
/ us-gaap_GainLossOnInvestmentsByCategoryAxis
= us-gaap_AvailableforsaleSecuritiesMember