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Capitalization - Initial Public Offering (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Sep. 26, 2016
Dec. 31, 2016
Class of Stock [Line Items]    
Net proceeds from the offering   $ 78,120
Class B common stock    
Class of Stock [Line Items]    
Stock issued in net exercise of warrants (in shares) 448,545  
Number of shares issued for automatic conversion of convertible preferred stock 22,078,637  
Number of common stock shares issued for each share of convertible preferred stock 0.3333  
IPO    
Class of Stock [Line Items]    
IPO price (in dollars per share) $ 18.00  
Net proceeds from the offering $ 78,100  
Underwriting commissions and discounts 5,900  
Offering costs—IPO 4,500  
Offering costs reclassified from other assets to additional paid-in capital $ 4,500  
IPO | Class A common stock    
Class of Stock [Line Items]    
Number of shares issued and sold by the Company 4,666,667  
Number of shares sold by selling shareholders 700,000  
Convertible Preferred Stock Warrants    
Class of Stock [Line Items]    
Outstanding warrants converted during the period (in shares) 1,382,505  
Class B Common Stock Warrants    
Class of Stock [Line Items]    
Warrants issued in conversion (in shares) 460,834  
Stock issued in net exercise of warrants (in shares) 448,545