Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $)
In Thousands, except Share data, unless otherwise specified
Common Stock.
Additional Paid-In Capital
Deficit Accumulated During the Development Stage
Accumulated Other Comprehensive Loss
Series A preferred stock
Series A-1 preferred stock
Total
Balance at Dec. 31, 2011   $ 201 $ (30,233)       $ (30,032)
Balance at Dec. 31, 2011         23,975    
Balance (in shares) at Dec. 31, 2011 307,742            
Increase (Decrease) in Stockholders' Equity              
Exercise of stock options   41         41
Exercise of stock options (in shares) 38,736            
Beneficial conversion feature from issuance of convertible notes   288         288
Stock-based compensation   80         80
Net loss     (11,742)       (11,742)
Balance at Dec. 31, 2012   610 (41,975)   23,975   (41,365)
Balance (in shares) at Dec. 31, 2012 346,478            
Increase (Decrease) in Temporary Equity              
Issuance of preferred stock in exchange for convertible promissory notes, net of issuance costs         16,623 7,750  
Issuance of preferred stock in exchange for convertible promissory notes, net of issuance costs (in shares)         16,623,092 6,750,000  
Issuance of Series A preferred stock, net of issuance costs         16,880    
Issuance of Series A preferred stock, net of issuance costs (in shares)         17,000,000    
Preferred shares converted into common stock 9 65,216     (57,478) (7,750) 65,225
Preferred shares converted into common stock (in shares) 9,210,999       (57,598,092) (6,750,000)  
Increase (Decrease) in Stockholders' Equity              
Early exercise of stock options and vesting of restricted stock   21         21
Early exercise of stock options and vesting of restricted stock (in shares) 25,765            
Issuance of common stock from public offering, net of issuance costs 6 72,188         72,194
Issuance of common stock from public offering, net of issuance costs (in shares) 5,750,000            
Reclassification of warrants from liabilities to equity   2,852         2,852
Exercise of stock options   28         28
Exercise of stock options (in shares) 24,171            
Stock-based compensation   1,227         1,227
Other comprehensive loss       (3)     (3)
Net loss     (26,088)       (26,088)
Balance at Dec. 31, 2013 15 142,142 (68,063) (3)     74,091
Balance (in shares) at Dec. 31, 2013 15,357,413           15,357,413
Increase (Decrease) in Stockholders' Equity              
Early exercise of stock options and vesting of restricted stock   39         39
Issuance of common stock from public offering, net of issuance costs 5 91,620         91,625
Issuance of common stock from public offering, net of issuance costs (in shares) 4,887,500            
Issued warrants in connection with debt issuance   78         78
Exercise of stock options   473         473
Exercise of stock options (in shares) 107,963           107,963
Stock-based compensation   3,679         3,679
Other comprehensive loss       (56)     (56)
Net loss     (36,375)       (36,375)
Balance at Dec. 31, 2014 $ 20 $ 238,031 $ (104,438) $ (59)     $ 133,554