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Summary of Significant Accounting Policies - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Cash Equivalents    
Assets, fair value $ 6,424  
Marketable securities:    
Assets, fair value 6,424  
Assets, fair value 6,424  
Warrant Liability [Member]    
Liabilities:    
Liabilities, fair value 13,871 $ 13,198
Money Market Funds [Member]    
Cash Equivalents    
Assets, fair value 4,603 30,318
Marketable securities:    
Assets, fair value 4,603 30,318
Assets, fair value 4,603 30,318
Asset Backed Securities [Member]    
Cash Equivalents    
Assets, fair value 900  
Marketable securities:    
Assets, fair value 900  
Assets, fair value 900  
Corporate Notes [Member]    
Cash Equivalents    
Assets, fair value 921  
Marketable securities:    
Assets, fair value 921  
Assets, fair value 921  
Quoted Prices in Active Markets (Level 1) [Member]    
Cash Equivalents    
Assets, fair value 4,603  
Marketable securities:    
Assets, fair value 4,603  
Assets, fair value 4,603  
Quoted Prices in Active Markets (Level 1) [Member] | Money Market Funds [Member]    
Cash Equivalents    
Assets, fair value 4,603 30,318
Marketable securities:    
Assets, fair value 4,603 30,318
Assets, fair value 4,603 30,318
Significant Other Observable Inputs (Level 2) [Member]    
Cash Equivalents    
Assets, fair value 1,821  
Marketable securities:    
Assets, fair value 1,821  
Assets, fair value 1,821  
Significant Other Observable Inputs (Level 2) [Member] | Asset Backed Securities [Member]    
Cash Equivalents    
Assets, fair value 900  
Marketable securities:    
Assets, fair value 900  
Assets, fair value 900  
Significant Other Observable Inputs (Level 2) [Member] | Corporate Notes [Member]    
Cash Equivalents    
Assets, fair value 921  
Marketable securities:    
Assets, fair value 921  
Assets, fair value 921  
Significant Unobservable Inputs (Level 3) [Member] | Warrant Liability [Member]    
Liabilities:    
Liabilities, fair value $ 13,871 $ 13,198