Summary of Significant Accounting Policies - Common Stock Warrants (Details) - USD ($)
 3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Feb. 12, 2015
Dec. 31, 2014
Dec. 16, 2014
Jun. 12, 2014
Common Stock Warrants                
Change in fair value of warrants $ 0 $ (41,000) $ 482,000 $ (41,000)        
Amended Mezzanine Loan and Security Agreement                
Common Stock Warrants                
Number of shares of common stock that may be purchased based on lender warrants issued           150,000    
Exercise price of warrants (in usd per share)           $ 11.36    
Change in fair value of warrants $ 0   $ 500,000          
Amended Mezzanine Loan and Security Agreement | Amended Term Loan - First Tranche                
Common Stock Warrants                
Number of shares of common stock that may be purchased based on lender warrants issued               100,000
Exercise price of warrants (in usd per share)               $ 11.36
Fair value of warrants               $ 900,000
Total face amount of debt               10,000,000
Amended Mezzanine Loan and Security Agreement | Amended Term Loan - Second Tranche                
Common Stock Warrants                
Number of shares of common stock that may be purchased based on lender warrants issued             50,000  
Exercise price of warrants (in usd per share)             $ 11.36  
Borrowing capacity remaining               $ 5,000,000
Total face amount of debt             $ 5,000,000  
Amended Mezzanine Loan and Security Agreement | Amended Term Loan - 2015 Term Loan                
Common Stock Warrants                
Number of shares of common stock that may be purchased based on lender warrants issued         50,000      
Exercise price of warrants (in usd per share)         $ 15.18      
Fair value of warrants         $ 300,000      
Total face amount of debt         $ 5,000,000