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Net Loss per Share - Schedule of Anti-dilutive Securities Excluded from 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]    
Anti-dilutive securities excluded from computation of diluted net loss per share 1,531,016 4,517,992
Employee Stock Option [Member]    
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]    
Anti-dilutive securities excluded from computation of diluted net loss per share 1,037,089 538,429
Warrant [Member]    
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]    
Anti-dilutive securities excluded from computation of diluted net loss per share 493,927 423,416
Convertible Preferred Stock [Member]    
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]    
Anti-dilutive securities excluded from computation of diluted net loss per share   3,556,147