Statements of Convertible Preferred Stock and Stockholders' (Deficit) Equity - USD ($)
$ in Thousands
Total
Initial Public Offering [Member]
Private Placement [Member]
Follow On Public Offering [Member]
Common Stock [Member]
Common Stock [Member]
Initial Public Offering [Member]
Common Stock [Member]
Private Placement [Member]
Common Stock [Member]
Follow On Public Offering [Member]
Additional Paid-In Capital [Member]
Additional Paid-In Capital [Member]
Initial Public Offering [Member]
Additional Paid-In Capital [Member]
Private Placement [Member]
Additional Paid-In Capital [Member]
Follow On Public Offering [Member]
Accumulated Deficit [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
Convertible Preferred Stock [Member]
Balance, Value at Dec. 31, 2013                             $ 65,586
Balance, Value at Dec. 31, 2013 $ (54,075)       $ 4       $ 8,377       $ (62,456)    
Sale of common stock, net of underwriting discounts and commissions and offering expenses, Value   $ 56,297 $ 100     $ 6       $ 56,291 $ 100        
Balance, Shares at Dec. 31, 2013                             29,186,929
Balance, Shares at Dec. 31, 2013         4,288,243                    
Sale of common stock, net of underwriting discounts and commissions and offering expenses, Shares           5,750,000 11,442                
Preferred stock converted to common shares, Value 65,586       $ 13       65,573           $ (65,586)
Preferred stock converted to common shares, Shares         12,554,171                   (29,186,929)
Stock-based compensation expense 1,371               1,371            
Shares issued upon exercise of stock options, Value 128               128            
Shares issued upon exercise of stock options, Shares         191,800                    
Shares issued upon cashless exercise of warrants, Value 0       $ 0       0       0 $ 0 $ 0
Shares issued upon cashless exercise of warrants, Shares         6,383                    
Net loss (17,745)                       (17,745)    
Balance, Value at Dec. 31, 2014 $ 51,662       $ 23       131,840       (80,201)    
Balance, Shares at Dec. 31, 2014 0                            
Balance, Shares at Dec. 31, 2014         22,802,039                    
Sale of common stock, net of underwriting discounts and commissions and offering expenses, Value       $ 75,231       $ 4       $ 75,227      
Sale of common stock, net of underwriting discounts and commissions and offering expenses, Shares               4,327,956              
Stock-based compensation expense $ 2,514               2,514            
Shares issued upon exercise of stock options, Value 362               362            
Shares issued upon exercise of stock options, Shares         124,868                    
Net loss (24,690)                       (24,690)    
Other comprehensive income (loss) (35)                         (35)  
Balance, Value at Dec. 31, 2015 $ 105,044       $ 27       209,943       (104,891) (35)  
Balance, Shares at Dec. 31, 2015 0                            
Balance, Shares at Dec. 31, 2015         27,254,863                    
Stock-based compensation expense $ 2,800               2,800            
Shares issued upon exercise of stock options, Value 123               123            
Shares issued upon exercise of stock options, Shares         42,000                    
Net loss (57,280)                       (57,280)    
Other comprehensive income (loss) 38                         38  
Balance, Value at Dec. 31, 2016 $ 50,725       $ 27       $ 212,866       $ (162,171) $ 3  
Balance, Shares at Dec. 31, 2016 0                            
Balance, Shares at Dec. 31, 2016         27,296,863