Quarterly report pursuant to Section 13 or 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
 3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of Anti-dilutive Securities 5,957,190 7,693,024 3,623,748 7,412,375
Redeemable Convertible Preferred Stock [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of Anti-dilutive Securities   4,921,382   4,830,323
Stock Options [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of Anti-dilutive Securities 4,432,611 687,258 2,636,548 660,762
Warrant [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of Anti-dilutive Securities 1,524,579 1,348,308 987,200 1,185,214
Convertible Notes Payable [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of Anti-dilutive Securities   736,076   736,076