Convertible Preferred Stock and Stockholders' Equity (Details) (USD $)
 12 Months Ended 0 Months Ended 1 Months Ended 0 Months Ended
Dec. 31, 2013
Apr. 19, 2013
Feb. 28, 2013
Feb. 28, 2013
Jul. 02, 2013
May 29, 2013
Apr. 28, 2008
Jan. 31, 2012
Nov. 30, 2012
Convertible preferred stock and stockholders' deficit                  
Proceeds from issuance of preferred stock, net of issuance costs $ 16,824,000                
Pfizer note                  
Convertible preferred stock and stockholders' deficit                  
Interest rate (as a percent)             8.931%    
Aggregate principal amount             5,000,000    
Outstanding principal amount           7,800,000      
Short term convertible notes issued January 2012                  
Convertible preferred stock and stockholders' deficit                  
Interest rate (as a percent)               10.00%  
Aggregate principal amount               6,000,000  
Short term convertible notes issued September and November 2012                  
Convertible preferred stock and stockholders' deficit                  
Interest rate (as a percent)                 10.00%
Aggregate principal amount                 9,700,000
Common stock | Warrant                  
Convertible preferred stock and stockholders' deficit                  
Share price of preferred stock (in dollars per share)         6.99        
Series A preferred stock                  
Convertible preferred stock and stockholders' deficit                  
Conversion of convertible promissory notes into Series A preferred stock (in shares) 16,623,092                
Preferred stock, shares authorized   17,000,000              
Share price of preferred stock (in dollars per share)   $ 1.00              
Proceeds from issuance of preferred stock, net of issuance costs   16,900,000              
Stock issuance costs (120,000) 100,000              
Conversion rate   0.143              
Number of shares of convertible preferred stock converted into common stock (57,598,092)                
Series A preferred stock | 10% Convertible promissory notes                  
Convertible preferred stock and stockholders' deficit                  
Aggregate principal amount     15,700,000 15,700,000          
Accrued interest     900,000 900,000          
Conversion of convertible promissory notes into Series A preferred stock (in shares)     16,623,092 16,623,092          
Conversion price (in dollars per share)     $ 1.00 $ 1.00          
Conversion rate     0.143 0.143          
Series A-1 preferred stock                  
Convertible preferred stock and stockholders' deficit                  
Conversion of convertible promissory notes into Series A preferred stock (in shares) 6,750,000                
Stock issuance costs $ 53,000                
Number of shares of convertible preferred stock converted into common stock (6,750,000)                
Series A-1 preferred stock | Pfizer note                  
Convertible preferred stock and stockholders' deficit                  
Preferred stock, shares authorized           6,750,000      
Share price of preferred stock (in dollars per share)           $ 1.1560      
Conversion rate           0.143      
Number of shares of convertible preferred stock converted into common stock         966,218        
Initial Public Offering | Common stock                  
Convertible preferred stock and stockholders' deficit                  
Number of shares of convertible preferred stock converted into common stock         9,210,999        
Initial Public Offering | Series A preferred stock                  
Convertible preferred stock and stockholders' deficit                  
Number of shares of convertible preferred stock converted into common stock         8,244,781        
Initial Public Offering | Series A-1 preferred stock                  
Convertible preferred stock and stockholders' deficit                  
Number of shares of convertible preferred stock converted into common stock         966,218