Consolidated Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)
$ in Thousands
Total
Series E Redeemable Convertible Preferred Stock [Member]
IPO [Member]
Series A, B-1, B-2, C,D-1, D-2, D-3 and E Redeemable Convertible Preferred Stock [Member]
Series A, B-1, B-2, C,D-1, D-2, D-3 and E Redeemable Convertible Preferred Stock [Member]
Series E Redeemable Convertible Preferred Stock [Member]
Common Stock [Member]
Common Stock [Member]
IPO [Member]
Additional Paid-in Capital [Member]
Additional Paid-in Capital [Member]
Series E Redeemable Convertible Preferred Stock [Member]
Additional Paid-in Capital [Member]
IPO [Member]
Accumulated Other Comprehensive Loss [Member]
Accumulated Deficit [Member]
Beginning Balance at Dec. 31, 2012 $ (39,901)             $ 7,429       $ (47,330)
Issuance of common stock upon exercise of stock options 215             215        
Beginning Balance at Dec. 31, 2012       $ 49,845                
Issuance of common stock upon exercise of stock options, Shares           157,804            
Beginning Balance, Shares at Dec. 31, 2012       98,693,750                
Beginning Balance, Shares at Dec. 31, 2012           464,633            
Accretion of redeemable convertible preferred stock to redemption value   $ (94)             $ (94)      
Accretion of redeemable convertible preferred stock to redemption value 94       $ 94              
Stock-based compensation expense 238             238        
Net loss (15,725)                     (15,725)
Ending Balance at Dec. 31, 2013 (55,267)             7,788       (63,055)
Ending Balance at Dec. 31, 2013       $ 85,345                
Ending Balance, Shares at Dec. 31, 2013           493,292            
Ending Balance, Shares at Dec. 31, 2013       155,586,141                
Repurchase and forfeiture of unvested restricted stock, Shares           (129,145)            
Conversion of preferred stock to common stock         $ 35,406              
Conversion of preferred stock to common stock, Shares         56,892,391              
Issuance of common stock upon exercise of stock options 16             16        
Issuance of common stock upon initial public offering     $ 97,929       $ 7     $ 97,922    
Issuance of common stock upon exercise of stock options, Shares           8,875            
Issuance of common stock upon initial public offering, Shares             7,020,000          
Issuance costs (3,334)             (3,334)        
Stock-based compensation expense 2,108             2,108        
Net loss (23,296)                     (23,296)
Ending Balance at Dec. 31, 2014 103,501         $ 22   189,830       (86,351)
Ending Balance, Shares at Dec. 31, 2014           22,382,340            
Conversion of preferred stock to common stock 85,345     $ (85,345)   $ 15   85,330        
Conversion of preferred stock to common stock, Shares       (155,586,141)   14,860,173            
Issuance of common stock upon exercise of stock options $ 464         $ 1   463        
Issuance of common stock upon exercise of stock options, Shares 201,153         201,153            
Issuance of common stock upon vesting of restricted stock units $ 0     $ 0   $ 0   0     $ 0 0
Issuance of common stock upon vesting of restricted stock units, Shares           13,651            
Stock-based compensation expense 2,901             2,901        
Unrealized loss on marketable securities (55)                   (55)  
Net loss (45,087)                     (45,087)
Ending Balance at Dec. 31, 2015 $ 61,724         $ 23   $ 193,194     $ (55) $ (131,438)
Ending Balance, Shares at Dec. 31, 2015           22,597,144