Quarterly report pursuant to Section 13 or 15(d)

Redeemable Convertible Preferred Stock - Summary of Redeemable Convertible Preferred Stock (Detail)

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Redeemable Convertible Preferred Stock - Summary of Redeemable Convertible Preferred Stock (Detail) - $ / shares
Sep. 30, 2017
Dec. 31, 2016
Temporary Equity [Line Items]    
Redeemable convertible preferred stock, shares authorized 9,165,279  
Redeemable convertible preferred stock, shares issued and outstanding   9,116,405
Series A Preferred Stock    
Temporary Equity [Line Items]    
Redeemable convertible preferred stock, par value $ 0.001  
Redeemable convertible preferred stock, shares authorized 2,500,000  
Redeemable convertible preferred stock, shares issued and outstanding   2,500,000
Series B Preferred Stock    
Temporary Equity [Line Items]    
Redeemable convertible preferred stock, par value $ 0.001  
Redeemable convertible preferred stock, shares authorized 2,273,531  
Redeemable convertible preferred stock, shares issued and outstanding   2,273,531
Series C Preferred Stock    
Temporary Equity [Line Items]    
Redeemable convertible preferred stock, par value $ 0.001  
Redeemable convertible preferred stock, shares authorized 4,391,748  
Redeemable convertible preferred stock, shares issued and outstanding   4,342,874