Statements of Changes in Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)
$ in Thousands
IPO
Common Stock
IPO
Additional Paid-In Capital
IPO
Convertible Preferred Stock.
Series A convertible preferred stock
Series B convertible preferred stock
Series A and Series B convertible preferred stock
Common Stock
Additional Paid-In Capital
Accumulated Other Comprehensive Income
Accumulated Deficit
Total
Balance (in shares) at Dec. 31, 2014       3,395,468       1,046,749        
Increase (Decrease) in Shares                        
Issuance of common stock to founders, net of repurchase (in shares)               384,866        
Issuance of stock (in shares)         5,525,961 5,353,312            
Balance (in shares) at Dec. 31, 2015       14,274,741       1,431,615        
Increase (Decrease) in Convertible Preferred Stock                        
Issuance of convertible preferred stock         $ 20,730 $ 74,839            
Reclassification of convertible preferred stock liability       $ 20,200                
Balance at Dec. 31, 2015       125,780 $ 50,941 $ 74,839           $ 125,780
Balance at Dec. 31, 2014       $ 10,011         $ 2   $ (161) (159)
Increase (Decrease) in Stockholders' Deficit                        
Issuance of common stock for cash upon early exercise of stock options and lapse of restrictions                 10     10
Stock-based compensation expense                 428     428
Unrealized loss on marketable securities                   $ (45)   (45)
Net loss                     (31,335) (31,335)
Balance at Dec. 31, 2015                 440 (45) (31,496) (31,101)
Increase (Decrease) in Shares                        
Number of common stock issued with the conversion of the preferred stock (in shares)             (14,274,741) 14,274,741        
Issuance of stock (in shares) 5,202,618                      
Issuance of common stock on exercise of stock options (in shares)               13,454        
Balance (in shares) at Dec. 31, 2016               20,922,428        
Increase (Decrease) in Stockholders' Deficit                        
Conversion of convertible preferred stock into common stock             $ (125,780) $ 1 125,779     125,780
Issuance of common stock $ 1 $ 70,624 $ 70,625                  
Common stock issued on exercise of stock options                 4     4
Vesting of restricted stocks issued upon early exercise of stock options                 34     34
Stock-based compensation expense                 3,828     3,828
Unrealized loss on marketable securities                   6   6
Net loss                     (36,375) (36,375)
Balance at Dec. 31, 2016               $ 2 $ 200,709 $ (39) $ (67,871) $ 132,801