Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Reconciliation of Warrant Liability Measured at Fair Value (Detail)

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Stockholders' Equity - Reconciliation of Warrant Liability Measured at Fair Value (Detail) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Change in fair value during the nine months ended September 30, 2018 $ 916 $ (269)
Basis of Fair Value Measurements, Level 3    
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]    
Beginning Balance 954  
Change in fair value during the nine months ended September 30, 2018 (916)  
Ending Balance $ 38