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Redeemable Convertible Preferred Stock - Preferred Stock and Warrants Calculated Using the Black Scholes Merton Pricing Model (Detail)
 12 Months Ended
Dec. 31, 2018
$ / shares
shares
Mar. 23, 2017
$ / shares
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Number of warrants | shares 325,000  
Weighted-average fair value of warrants $ 3.11 $ 0.73
Expiration date May 02, 2020  
Exercise Price    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Warrants outstanding, measurement input 6.62  
Expected Volatility of Underlying Stock    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Warrants outstanding, measurement input 0.74 0.72
Risk-Free Interest Rate    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Warrants outstanding, measurement input 0.0162 0.0208
Dividend Yield    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Warrants outstanding, measurement input 0.00 0.00
Expected Life of Warrants    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Expected life of warrants 8 years 5 years