Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Effect of Anti-dilutive Securities (Detail)

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Summary of Significant Accounting Policies - Effect of Anti-dilutive Securities (Detail) - shares
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Effect of Anti-dilutive Securities 4,268,984 9,748,469
Redeemable Convertible Preferred Stock [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Effect of Anti-dilutive Securities   5,083,932
Employee Stock Option and Restricted Stock Units [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Effect of Anti-dilutive Securities 3,148,931 680,437
Warrant [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Effect of Anti-dilutive Securities 1,120,053 2,493,449
Conversion of Convertible Note Payable [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Effect of Anti-dilutive Securities   1,490,651