CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Class of Stock [Line Items]    
Issuance costs $ 845 $ 2,408
Series D convertible redeemable preferred stock    
Class of Stock [Line Items]    
Issuance costs   193
Initial public offering | Common stock    
Class of Stock [Line Items]    
Issuance costs $ 845 $ 2,408