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Liquidity (Details) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 9 Months Ended
Oct. 31, 2017
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Subsidiary, Sale of Stock [Line Items]        
Cash and cash equivalents   $ 49,410   $ 36,797
Proceeds from the sale of Series D preferred stock   $ 36,494 $ 0  
Redeemable Convertible Preferred Stock, Series D        
Subsidiary, Sale of Stock [Line Items]        
Number of shares issued (in shares)   1,117,578    
Proceeds from the sale of Series D preferred stock   $ 36,712    
Price per share (usd per share)   $ 32.85    
Subsequent Event | IPO        
Subsidiary, Sale of Stock [Line Items]        
Price per share (usd per share) $ 16.00      
Proceeds from IPO $ 125,540      
Fees and commissions 9,660      
Stock issuance costs $ 2,800