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Net Loss per Share - Summary of Shares Excluded From the Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) - shares
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 6,352,943 2,129,082
Options to Purchase Common Stock [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 3,082,943 2,129,082
Unvested Restricted Stock Units [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 50,000  
Series A Convertible Preferred Stock [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 2,220,000  
Series B Convertible Preferred Stock [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 1,000,000