Stockholders' Equity (Deficit) - Additional Information (Detail) (USD $)
 0 Months Ended 1 Months Ended 3 Months Ended
Feb. 18, 2015
Feb. 28, 2015
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Class Of Warrant Or Right [Line Items]          
Common stock sold, shares 8,300,000        
Warrants to purchase shares of common stock 8,300,000        
Proceeds from issuance of common stock and warrants, net of offering expenses $ 28,100,000   $ 28,514,000 $ 345,000  
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 Offering          
Class Of Warrant Or Right [Line Items]          
Warrants outstanding 8,300,000   8,300,000    
Warrant exercise price $ 10.86   $ 10.86    
February 2015 Offering | 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     1,200,000    
March 2011 Offering          
Class Of Warrant Or Right [Line Items]          
Warrants outstanding     3,846,165   3,846,165
Warrant exercise price     $ 2.46   $ 2.46
March 2011 Offering | Warrants          
Class Of Warrant Or Right [Line Items]          
Change in fair value of common stock warrants     $ 2,700,000