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Cash, Cash Equivalents and Marketable Securities - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]      
Realized gains or losses from the sale of marketable securities $ 0us-gaap_MarketableSecuritiesRealizedGainLoss $ 0us-gaap_MarketableSecuritiesRealizedGainLoss $ 0us-gaap_MarketableSecuritiesRealizedGainLoss