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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
Mar. 31, 2019
Dec. 31, 2018
Assets:    
Money market funds, fair value $ 4,747 $ 9,711
Liabilities:    
Warrant liability, fair value 10 2,512
Quoted Prices in Active Markets (Level 1) [Member]    
Assets:    
Money market funds, fair value 4,747 9,711
Significant Unobservable Inputs (Level 3) [Member]    
Liabilities:    
Warrant liability, fair value $ 10 $ 2,512