Debt Financing (Details) - Convertible promissory notes - USD ($)
1 Months Ended 12 Months Ended
May. 08, 2012
May. 31, 2013
Dec. 31, 2013
Debt financing      
Cash proceeds received $ 23,100,000    
Interest rate 10.00%    
Gross proceeds (at least) $ 25,000,000.0    
Conversion price upon automatic conversion (as a percent) (to the lower of) 85.00%    
Conversion price upon automatic conversion (in dollars per share) $ 12.08    
Conversion price per share (as a percent) (to the greater of) 85.00%    
Conversion price convertible at the option of the holder if change in control or initial public offering occurs prior to maturity date (in dollars per share) $ 7.95    
Conversion price convertible at the option of the holder if change in control or initial public offering does not occur prior to the maturity date (in dollars per share) 7.16    
Conversion price (in dollars per share) $ 7.16 $ 7.16  
Beneficial conversion feature $ 2,700,000    
Interest expense     $ 800,000
Amortization of debt discount     $ 900,000
Common stock issued on conversion (in shares)   3,556,412