Long-term Debt - Additional Information (Detail) - USD ($)
 12 Months Ended
Apr. 07, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Feb. 11, 2014
Feb. 04, 2014
Mar. 26, 2009
Debt Instrument [Line Items]              
Estimated fair value of outstanding warrants           $ 800,000  
Common stock issued, shares   20,594,575 17,786,867        
Adjustment to preferred stock warrant liability recorded in other income (expense)     $ (2,559,000) $ (126,000)      
Hercules Warrants [Member]              
Debt Instrument [Line Items]              
Adjustment to preferred stock warrant liability recorded in other income (expense)   $ 0 (700,000) $ 200,000      
Series A Warrants [Member]              
Debt Instrument [Line Items]              
Estimated fair value of outstanding warrants   0 0        
Series B Warrants [Member]              
Debt Instrument [Line Items]              
Estimated fair value of outstanding warrants   $ 0 $ 0        
Second Amendment [Member]              
Debt Instrument [Line Items]              
Annual interest rate 10.15%            
Principal monthly installments period   December 31, 2013 through April 7, 2014          
Hercules Loan [Member]              
Debt Instrument [Line Items]              
Loan and security agreement amount             $ 7,000,000
Repayment of debt $ 3,600,000            
IPO closing date   Feb. 04, 2014          
Common stock issued, shares         12,702    
Hercules Loan [Member] | Series A Warrants [Member]              
Debt Instrument [Line Items]              
Warrants exercised, number of shares   21,000          
Warrants exercised, exercise price   $ 25.00          
Hercules Loan [Member] | Series B Warrants [Member]              
Debt Instrument [Line Items]              
Warrants exercised, number of shares   26,400          
Warrants exercised, exercise price   $ 25.00