Annual report pursuant to Section 13 and 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
Dec. 31, 2017
Dec. 31, 2016
Temporary Equity [Line Items]    
Redeemable convertible preferred stock, shares authorized   9,165
Redeemable convertible preferred stock, shares issued and outstanding 0 9,116
Series A Preferred Stock    
Temporary Equity [Line Items]    
Redeemable convertible preferred stock, par value   $ 0.001
Redeemable convertible preferred stock, shares authorized   2,500
Redeemable convertible preferred stock, shares issued and outstanding 0 2,500
Series B Preferred Stock    
Temporary Equity [Line Items]    
Redeemable convertible preferred stock, par value   $ 0.001
Redeemable convertible preferred stock, shares authorized   2,273
Redeemable convertible preferred stock, shares issued and outstanding 0 2,273
Series C Preferred Stock    
Temporary Equity [Line Items]    
Redeemable convertible preferred stock, par value   $ 0.001
Redeemable convertible preferred stock, shares authorized   4,392
Redeemable convertible preferred stock, shares issued and outstanding 0 4,343