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Marketable Investments - Summary of Company's Fair Value Hierarchy for its Financial Assets (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of assets on recurring basis $ 61,677us-gaap_AssetsFairValueDisclosureRecurring $ 56,679us-gaap_AssetsFairValueDisclosureRecurring
Money Market Funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of assets on recurring basis 845us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
1,794us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
Corporate Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of assets on recurring basis 60,832us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
54,885us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of assets on recurring basis 845us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
1,794us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Level 1 [Member] | Money Market Funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of assets on recurring basis 845us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
1,794us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of assets on recurring basis 60,832us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
54,885us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Level 2 [Member] | Corporate Obligations [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of assets on recurring basis $ 60,832us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
$ 54,885us-gaap_AssetsFairValueDisclosureRecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember