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Net Income Loss Per Share - Effect of Anti-dilutive Securities (Detail) - shares
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Effect of Anti-dilutive Securities 14,519,901 6,228,374
Employee Stock Option and Restricted Stock Units [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Effect of Anti-dilutive Securities 13,222,750 4,703,801
Warrant [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Effect of Anti-dilutive Securities 1,297,151 1,524,573