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Redeemable Convertible Preferred Stock - Additional Information (Detail) - USD ($)
 1 Months Ended 12 Months Ended
Apr. 30, 2016
Aug. 31, 2014
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Aug. 16, 2016
Temporary Equity [Line Items]            
Redeemable convertible preferred stock, shares issued     0 77,185,117    
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants     $ 22,488,000 $ 17,362,000 $ 9,000,000  
Shares issued upon conversion of preferred stock           8,577,571
Redeemable convertible preferred stock, shares outstanding     0 77,185,117    
Redeemable convertible preferred stock redemption date     2022-07      
Redeemable convertible preferred stock, period accretion     $ 558,000 $ 75,000 $ 146,000  
Series B Redeemable Convertible Preferred Stock [Member]            
Temporary Equity [Line Items]            
Redeemable convertible preferred stock, shares issued 1,999,998 18,000,000        
Proceeds from issuance of redeemable convertible preferred stock upon exercise of warrants $ 20,000 $ 9,000,000