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Fair Value Measurements - Fair Value of Preferred Stock Warrant Liability Calculated by Black-Scholes Option Pricing Model (Detail)
12 Months Ended
Dec. 31, 2013
Minimum [Member]  
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]  
Expected life 4 years
Risk-free interest rate 2.90%us-gaap_FairValueAssumptionsRiskFreeInterestRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Expected volatility 64.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum [Member]  
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]  
Expected life 8 years
Risk-free interest rate 2.90%us-gaap_FairValueAssumptionsRiskFreeInterestRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Expected volatility 84.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember