Loan and Security Agreement (Details) (USD $)
 1 Months Ended 0 Months Ended 1 Months Ended 12 Months Ended 0 Months Ended
May 31, 2014
Jun. 11, 2014
May 30, 2014
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May 30, 2014
Dec. 31, 2014
Jul. 10, 2014
Oct. 07, 2014
Dec. 31, 2013
Jun. 06, 2014
May 23, 2011
Nov. 21, 2011
May 29, 2012
Loan and Security Agreement                        
Maximum borrowing limit     $ 30,000,000 $ 30,000,000                
Share issue price (in dollars per share)   8.00         $ 18.25          
Fair value of warrants issued (in dollars)               1,945,000        
Future principal payments under the Loan and Security Agreement                        
Current portion of Note payable, net of discount               13,005,000        
2016         10,000,000              
2017         10,000,000              
2018         5,000,000              
Total         25,000,000              
Series A-1 Convertible Preferred Stock | Maximum                        
Loan and Security Agreement                        
Conversion of convertible preferred stock, and associated accumulated dividends into common stock (in shares) 58,918                      
Series B-2 Convertible Preferred Stock                        
Loan and Security Agreement                        
Number of shares that can be purchased for warrants issued     10,258 10,258                
Exercise price of warrants (in dollars per unit)     $ 61.42 $ 61.42         $ 8.00      
Share issue price (in dollars per share)     $ 8.00 $ 8.00                
Series B-2 Convertible Preferred Stock | Maximum                        
Loan and Security Agreement                        
Conversion of convertible preferred stock, and associated accumulated dividends into common stock (in shares)   78,760                    
Initial Term Loan                        
Loan and Security Agreement                        
Aggregate principal amount     21,000,000 21,000,000                
Number of payments of principal and interest payable monthly in arrears     36                  
Minimum aggregate net cash proceeds required to be received to make interest only payments     65,000,000 65,000,000                
Number of interest and principal payments to be made if minimum required aggregate net cash proceeds are received     30                  
Fair value of warrants issued (in dollars)     300,000 300,000                
Payment of facility fees to lender     300,000                  
Payment of reimbursed costs to lender     100,000                  
Debt discount amortization period     48 months                  
Proceeds used to repay existing credit facility     9,300,000                  
Basis spread (as a percent) 9.85%                      
Variable interest rate, description one-month LIBOR                      
Second Term Loan                        
Loan and Security Agreement                        
Threshold net cash proceed as prerequisite to request term loan       65,000,000                
Additional Term Loan that Can be Requested if Threshold of IPO is Met     9,000,000                  
Basis spread (as a percent) 9.85%                      
Variable interest rate, description one-month LIBOR                      
Term Loan                        
Loan and Security Agreement                        
Maximum borrowing limit                   25,000,000    
Final payment fee (as a percent)         3.50%              
Prepayment fees as percentage of amount prepaid if the prepayment occurs prior to the first anniversary of the funding         3.00%              
Prepayment fees as percentage of amount prepaid if prepayment occurs between the first and second anniversary of the funding         2.00%              
Prepayment fees as percentage of amount prepaid if prepayment occurs on or after the second anniversary of the funding         1.00%              
Term Loan | Series A-1 Convertible Preferred Stock                        
Loan and Security Agreement                        
Number of shares that can be purchased for warrants issued         12,280              
Exercise price of warrants (in dollars per unit) 81.42                      
Term Loan A                        
Loan and Security Agreement                        
Aggregate principal amount                   6,300,000    
Number of payments of principal and interest payable monthly in arrears         36              
Final balloon payment         600,000              
Annual interest rate (as a percent)         10.16%              
Expiration term of warrants 10 years                      
Fair value of warrants issued (in dollars)                   182,600    
Payment of facility fees to lender         250,000              
Payment of reimbursed costs to lender         117,000              
Term Loan B                        
Loan and Security Agreement                        
Aggregate principal amount           4,000,000         6,300,000  
Number of payments of principal and interest payable monthly in arrears         30              
Final balloon payment         600,000              
Annual interest rate (as a percent)         10.00%              
Number of shares that can be purchased for warrants issued           4,706            
Exercise price of warrants (in dollars per unit)           $ 12.75            
Expiration term of warrants           5 years            
Fair value of warrants issued (in dollars)           41,000         177,600  
Payment of reimbursed costs to lender         18,000              
Term Loan C                        
Loan and Security Agreement                        
Aggregate principal amount                       12,500,000
Number of payments of principal and interest payable monthly in arrears         24              
Final balloon payment         1,300,000              
Annual interest rate (as a percent)         10.00%              
Fair value of warrants issued (in dollars)                       379,700
Payment of reimbursed costs to lender         31,000              
Term Loan C | Scenario, Forecast                        
Loan and Security Agreement                        
Aggregate principal amount         5,000,000              
Threshold net cash proceed as prerequisite to request term loan         13,000,000