Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail)

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Summary of Significant Accounting Policies - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($)
$ in Thousands
Sep. 30, 2015
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total assets measured at fair value $ 46,656 $ 33,150
Total liabilities measured at fair value 1,356 13,596
Warrant liability [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total liabilities measured at fair value 1,356 13,596
Money market funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total assets measured at fair value 5,294 9,941
Corporate debt and asset backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total assets measured at fair value 41,362 23,209
Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total assets measured at fair value 5,294 9,941
Level 1 [Member] | Money market funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total assets measured at fair value 5,294 9,941
Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total assets measured at fair value 41,362 23,209
Level 2 [Member] | Corporate debt and asset backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total assets measured at fair value 41,362 23,209
Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total liabilities measured at fair value 1,356 13,596
Level 3 [Member] | Warrant liability [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total liabilities measured at fair value $ 1,356 $ 13,596