Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)
$ in Thousands
Common stock
Additional paid-in capital
Accumulated Other Comprehensive Income (Loss)
Accumulated deficit
Total
Balance at the beginning of the period at Dec. 31, 2012   $ 91   $ (12,850) $ (12,759)
Balance at the beginning of the period (in shares) at Dec. 31, 2012 661,118        
Increase (Decrease) in Stockholders' Deficit          
Common stock issued on exercise of stock options   39     39
Common stock issued on exercise of stock options (in shares) 31,666        
Vesting of common stock related to early exercise of options   18     18
Vesting of common stock related to early exercise of options (in shares) 39,886        
Stock-based compensation expense   260     260
Net loss       (24,838) (24,838)
Balance at the end of the period at Dec. 31, 2013   408   (37,688) (37,280)
Balance at the end of the period (in shares) at Dec. 31, 2013 732,670        
Increase (Decrease) in Stockholders' Deficit          
Common stock issued on exercise of stock options   209     209
Common stock issued on exercise of stock options (in shares) 168,867        
Vesting of common stock related to early exercise of options   16     16
Vesting of common stock related to early exercise of options (in shares) 43,044        
Stock-based compensation expense   971     971
Net loss       (47,492) (47,492)
Balance at the end of the period at Dec. 31, 2014   1,604   (85,180) $ (83,576)
Balance at the end of the period (in shares) at Dec. 31, 2014 944,581       944,581
Increase (Decrease) in Stockholders' Deficit          
Conversion of preferred stock into common stock upon initial public offering costs (in shares) 23,521,889        
Conversion of preferred stock into common stock upon initial public offering costs $ 3 202,302     $ 202,305
Issuance of common stock in connection with initial public offering, net of offering costs (in shares) 7,302,500        
Issuance of common stock in connection with initial public offering, net of offering costs $ 1 105,667     105,668
Common stock issued on exercise of stock options   288     288
Common stock issued on exercise of stock options (in shares) 148,870        
Vesting of common stock related to early exercise of options   11     11
Vesting of common stock related to early exercise of options (in shares) 17,281        
Stock-based compensation expense   3,477     3,477
Unrealized loss on investments     $ (15)   (15)
Net loss       (89,782) (89,782)
Balance at the end of the period at Dec. 31, 2015 $ 4 $ 313,349 $ (15) $ (174,962) $ 138,376
Balance at the end of the period (in shares) at Dec. 31, 2015 31,935,121       31,935,121