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Cash Equivalents and Investments - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Cash and Cash Equivalents [Line Items]    
Investments in continuous unrealized loss position for 12 months or longer $ 0us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss  
U.S. Treasury Securities [Member]    
Cash and Cash Equivalents [Line Items]    
U.S. Treasury securities maturity start date Jan. 01, 2015  
U.S. Treasury securities maturity end date Feb. 27, 2015  
Short-term Investments [Member]    
Cash and Cash Equivalents [Line Items]    
Unrealized Gain (loss) $ (7,000)us-gaap_UnrealizedGainLossOnInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_ShortTermInvestmentsMember
$ (1,000)us-gaap_UnrealizedGainLossOnInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_ShortTermInvestmentsMember