Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity (Deficit) - Additional Information (Detail)

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Stockholders' Equity (Deficit) - Additional Information (Detail) - USD ($)
$ / shares in Units, shares in Millions
 1 Months Ended 3 Months Ended 9 Months Ended
Feb. 18, 2015
Feb. 28, 2015
Sep. 30, 2015
Sep. 30, 2015
Sep. 30, 2014
Dec. 31, 2014
Class Of Warrant Or Right [Line Items]            
Common stock sold, shares 8.3          
Warrants to purchase shares of common stock 8.3          
Proceeds from issuance of common stock and warrants, net of offering expenses $ 28,100,000     $ 28,845,000 $ 5,108,000  
Initial exercise price of the warrants   $ 10.86        
Maximum exercise price of warrants after adjustment date   10.86        
Minimum exercise price of warrants after adjustment date   $ 3.62        
Term of warrant   5 years        
Company can force exercise of warrant if 20 day VWAP price exceeds   $ 18.00        
February 2015 Warrants            
Class Of Warrant Or Right [Line Items]            
Warrants outstanding 8.3   8.3 8.3    
Warrant exercise price $ 10.86   $ 10.86 $ 10.86    
February 2015 Warrants | Warrants            
Class Of Warrant Or Right [Line Items]            
Initial fair value of warrants at issuance date classified as warrant liability $ 14,700,000          
Change in fair value of common stock warrants     $ 300,000 $ 1,700,000    
March 2011 Warrants            
Class Of Warrant Or Right [Line Items]            
Warrants outstanding     3.8 3.8   3.8
Warrant exercise price     $ 2.46 $ 2.46   $ 2.46
March 2011 Warrants | Warrants            
Class Of Warrant Or Right [Line Items]            
Change in fair value of common stock warrants     $ 38,000 $ 2,400,000