General form of registration statement for all companies including face-amount certificate companies

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

v3.8.0.1
Summary of Significant Accounting Policies - Effect of Anti-dilutive Securities (Detail) - shares
 9 Months Ended 12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of Anti-dilutive Securities 3,623,748 7,412,375 9,957,354 5,422,246
Redeemable Convertible Preferred Stock [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of Anti-dilutive Securities   4,830,323 5,083,932 4,708,398
Common stock subject to repurchase [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of Anti-dilutive Securities     208,885 79,650
Stock Options [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of Anti-dilutive Securities 2,636,548 660,762 680,437 634,198
Warrant [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Effect of Anti-dilutive Securities 987,200 1,185,214 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   736,076 1,490,651