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Warrants and Warrant Derivative Liability - Additional Information (Detail)
$ / shares in Units, $ in Thousands
 1 Months Ended 3 Months Ended
Oct. 16, 2009
USD ($)
$ / shares
shares
Oct. 31, 2009
Mar. 31, 2016
shares
Mar. 31, 2015
USD ($)
shares
Dec. 31, 2015
shares
Dec. 31, 2014
shares
Derivative [Line Items]            
Common stock issued under private placement, net proceeds | $       $ 52,800    
Warrants outstanding     0      
Proceeds from exercise of warrants | $       $ 2,713    
Warrants Issued October 2009            
Derivative [Line Items]            
Warrants outstanding     0   0 8,087,388
Warrants expiration date   Feb. 27, 2015        
Warrants exercised       1,844,585    
Proceeds from exercise of warrants | $       $ 2,700    
Warrants expired       6,242,803    
Warrants Issued October 2009 | Prior To Agreement            
Derivative [Line Items]            
Warrants expiration date Oct. 16, 2014          
October 2009 Private Placement            
Derivative [Line Items]            
Common stock issued under private placement, value | $ $ 70,000          
Common stock issued under private placement, net proceeds | $ $ 62,300          
Common stock issued under private placement, shares 66,400,000          
Number of shares that each ADS represents 1          
Common stock issued under private placement, price per share | $ / shares $ 1.00          
October 2009 Private Placement | Warrants issued to three former officers            
Derivative [Line Items]            
Number of warrants issued 900,000          
October 2009 Private Placement | Bridge Loan            
Derivative [Line Items]            
Bridge notes converted in conjunction with the private placement, amount | $ $ 3,600          
Common stock issued under private placement, shares 4,000,000          
Number of shares that each ADS represents 1          
Bridge notes converted in conjunction with the private placement, price per share | $ / shares $ 0.90          
October 2009 Private Placement | Warrants Issued October 2009            
Derivative [Line Items]            
Number of warrants issued 35,200,000          
Description of pricing variability feature and classification of warrants     The warrants issued in connection with the October 2009 financing contained a pricing variability feature which provided for an increase to the exercise price if the exchange rate between the U.S. dollar and British pound adjusts such that the warrants could be exercised at a price less than the £0.5 par value of the common stock - that is, if the exchange rate exceeded U.S. $3.00 per £1.0 sterling. Due to the potential variable nature of the exercise price, the warrants are not considered to be indexed to the Company’s common stock. Accordingly, the warrants do not qualify for the exception to classify the warrants within equity and are classified as a derivative liability.      
October 2009 Private Placement | Warrants Issued October 2009 | Maximum            
Derivative [Line Items]            
Warrants issued, number of shares called by the warrant 36,100,000          
October 2009 Private Placement | Warrants Issued October 2009 | American Depositary Share            
Derivative [Line Items]            
Warrant term 5 years          
Warrants issued, number of shares called by a warrant 0.5          
Exercise price of the warrants | $ / shares $ 1.50          
October 2009 Private Placement | Warrants Issued October 2009 | Bridge Loan | American Depositary Share            
Derivative [Line Items]            
Warrant term 5 years          
Warrants issued, number of shares called by a warrant 0.5          
Exercise price of the warrants | $ / shares $ 1.50