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Debt - Additional Information (Detail) - USD ($)
 3 Months Ended 9 Months Ended 12 Months Ended
Apr. 29, 2015
Dec. 19, 2014
Nov. 15, 2013
Jun. 05, 2012
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2015
Dec. 31, 2014
Mar. 31, 2013
Debt Instrument [Line Items]                    
Strike price per share $ 9.41                  
Interest expense         $ 200,000 $ 400,000   $ 800,000 $ 1,400,000  
Non-cash interest expense amortization of debt discount         100,000 100,000   300,000 500,000  
Proceeds from additional equity offering $ 22,300,000                  
Senior Secured Loan | Hercules Technology Growth Capital                    
Debt Instrument [Line Items]                    
Number of shares received from warrants received to purchase common stock   58,823                
Strike price per share $ 9.41 $ 11.00                
Term Loan | Senior Secured Loan | Hercules Technology Growth Capital                    
Debt Instrument [Line Items]                    
Number of shares received from warrants received to purchase common stock       13,927            
Strike price per share       $ 35.90            
Fair value of warrants at issuance       $ 400,000            
Debt, face amount       10,000,000            
Net proceeds from debt       $ 9,700,000            
Interest rate on loan       11.00%            
Interest expense                   $ 1,200,000
Non-cash interest expense amortization of debt discount                 100,000  
Covenant, unrestricted cash balance requirement     $ 5,000,000   2,000,000     $ 2,000,000    
Debt Instrument, Maturity Date, Description               As part of the Hercules Second Amendment, this Minimum Threshold was amended to be the lower of $5.0 million or the aggregate outstanding principal balance of the Term Loans. As a result of the Company’s April 2015 equity offering, the Minimum Threshold was reduced to the lesser of $2.0 million or the aggregate outstanding principal balance of the Term Loans.    
Repayments of term loan               $ 2,000,000    
Term Loan | Senior Secured Loan | Hercules Technology Growth Capital | Maximum                    
Debt Instrument [Line Items]                    
Non-cash interest expense amortization of debt discount           100,000        
Term Loan | Senior Secured Loan | Hercules Technology Growth Capital | Prime Rate | Minimum                    
Debt Instrument [Line Items]                    
Prime rate       3.75%            
Term Loan B | Senior Secured Loan | Hercules Technology Growth Capital                    
Debt Instrument [Line Items]                    
Number of shares received from warrants received to purchase common stock     25,641              
Strike price per share     $ 19.50              
Debt, face amount     $ 10,000,000              
Net proceeds from debt     $ 9,800,000              
Interest expense               1,000,000    
Legal and origination costs             $ 200,000      
End of term fee               500,000    
Total debt discount being amortized into interest expense         100,000 100,000   200,000 400,000  
Minimum amount of proceeds from specified asset dispositions for mandatory prepayment feature         1,000,000     1,000,000    
Outstanding principal balance         3,700,000     3,700,000    
Term Loan C | Senior Secured Loan | Hercules Technology Growth Capital                    
Debt Instrument [Line Items]                    
Number of shares received from warrants received to purchase common stock   58,823                
Strike price per share   $ 11.00                
Debt, face amount   $ 1,500,000                
Net proceeds from debt   $ 1,400,000                
Interest expense                 300,000  
Legal and origination costs           100,000        
End of term fee                 $ 100,000  
Debt Instrument, Maturity Date                 Jun. 01, 2017  
Term Loan C | Senior Secured Loan | Hercules Technology Growth Capital | Minimum                    
Debt Instrument [Line Items]                    
Proceeds from additional equity offering         10,000,000          
Term Loan C | Senior Secured Loan | Hercules Technology Growth Capital | Maximum                    
Debt Instrument [Line Items]                    
Non-cash interest expense amortization of debt discount         $ 100,000 $ 100,000   $ 100,000 $ 100,000