Debt (Details) (USD $)
 12 Months Ended 0 Months Ended 1 Months Ended 4 Months Ended 12 Months Ended 0 Months Ended 1 Months Ended
Dec. 31, 2013
Feb. 28, 2013
Feb. 28, 2013
Dec. 31, 2012
Dec. 31, 2014
Dec. 31, 2012
Jul. 02, 2013
Jun. 30, 2014
Apr. 19, 2013
Dec. 31, 2011
Jan. 31, 2012
Nov. 30, 2012
Sep. 30, 2012
May 29, 2013
Apr. 28, 2008
Debt                              
Deferred financing costs         $ 100,000                    
Series A preferred stock                              
Estimated future principal payments due under the Credit Facility                              
Conversion of convertible promissory notes into Series A preferred stock (in shares) 16,623,092                            
Preferred stock, shares issued       23,975,000   23,975,000       23,975,000          
Share price of preferred stock (in dollars per share)                 $ 1.00            
Number of shares of preferred stock converted into shares of common stock (57,598,092)                            
Series A-1 preferred stock                              
Estimated future principal payments due under the Credit Facility                              
Conversion of convertible promissory notes into Series A preferred stock (in shares) 6,750,000                            
Number of shares of preferred stock converted into shares of common stock (6,750,000)                            
Warrant                              
Debt                              
Exercise price (in dollars per share)         $ 7.23                    
Series A preferred stock warrant                              
Debt                              
Warrants exercisable into stock (in shares)             1,940,000                
Exercise price (in dollars per share)             1.00                
10% Convertible promissory notes | Series A preferred stock                              
Estimated future principal payments due under the Credit Facility                              
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                        
Short term convertible notes issued January 2012                              
Debt                              
Interest rate (as a percent)                     10.00%        
Estimated future principal payments due under the Credit Facility                              
Aggregate principal amount                     6,000,000        
Short term convertible notes issued September and November 2012                              
Debt                              
Interest rate (as a percent)                       10.00%      
Estimated future principal payments due under the Credit Facility                              
Aggregate principal amount                       9,700,000      
Short term borrowings with related parties, net of debt discount                       9,400,000      
Short term convertible notes issued September and November 2012 | Series A preferred stock warrant | Series A preferred stock                              
Estimated future principal payments due under the Credit Facility                              
Aggregate purchase price of warrants       9,700                      
Short term convertible notes issued September and November 2012 | Series A preferred stock warrant | Total                              
Estimated future principal payments due under the Credit Facility                              
Estimated fair value of warrants                       300,000      
Short term convertible notes issued September 2012                              
Estimated future principal payments due under the Credit Facility                              
Fair value of beneficial conversion feature     300,000                        
Short term convertible notes issued September 2012 | Interest Expense.                              
Estimated future principal payments due under the Credit Facility                              
Amortization of debt discount and beneficial conversion 200,000       200,000 100,000                  
Short term convertible notes issued September 2012 | Warrant | Total                              
Estimated future principal payments due under the Credit Facility                              
Estimated fair value of warrants                         100,000    
Pfizer note                              
Debt                              
Interest rate (as a percent)                             8.931%
Estimated future principal payments due under the Credit Facility                              
Aggregate principal amount                             5,000,000
Outstanding principal amount                           7,800,000  
Accrued interest during period 300,000         600,000                  
Pfizer note | Series A-1 preferred stock                              
Estimated future principal payments due under the Credit Facility                              
Preferred stock, shares issued                           6,750,000  
Share price of preferred stock (in dollars per share)                           $ 1.1560  
Number of shares of preferred stock converted into shares of common stock             966,218                
Credit Facility                              
Debt                              
Maximum borrowing capacity         20,000,000                    
Percentage of final payment equal to amount drawn under the Credit Facility         8.00%                    
Estimated future principal payments due under the Credit Facility                              
2015         638,000                    
2016         1,604,000                    
2017         1,709,000                    
2018         1,049,000                    
Total         5,000,000                    
Interest expense         300,000                    
Interest payments         100,000                    
Term A Loan                              
Debt                              
Maximum borrowing capacity         5,000,000                    
Period of consecutive equal monthly installments of principal and interest         36 months                    
Interest rate (as a percent)         6.40%                    
Term A Loan | Warrant                              
Debt                              
Warrants exercisable into stock (in shares)               8,230              
Exercise price (in dollars per share)               $ 15.19              
Unamortized discount               100,000              
Term A Loan | Secured promissory notes                              
Debt                              
Proceeds from issuance of debt               5,000,000              
Term B Loan                              
Debt                              
Maximum borrowing capacity         15,000,000                    
Remaining borrowing capacity         $ 15,000,000                    
Interest rate (as a percent)         6.40%                    
Reference rate         three month LIBOR                    
Number of business days prior to funding of new term loan         3 days                    
Interest rate margin (as a percent)         6.17%