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Warrants and Derivative Liability - Additional Information (Detail) (USD $)
 1 Months Ended 3 Months Ended 3 Months Ended 1 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended
Jan. 31, 2011
Mar. 31, 2012
Mar. 31, 2011
Dec. 31, 2011
Mar. 31, 2012
Warrants Issued October 2009
Mar. 31, 2011
Warrants Issued October 2009
Dec. 31, 2011
Warrants Issued October 2009
Dec. 31, 2010
Warrants Issued October 2009
Oct. 31, 2009
October 2009 Private Placement
Point
Oct. 31, 2009
October 2009 Private Placement
Bridge Loan
Point
Oct. 16, 2009
October 2009 Private Placement
Bridge Loan
Mar. 31, 2012
October 2009 Private Placement
Warrants Issued October 2009
Mar. 31, 2011
October 2009 Private Placement
Warrants Issued October 2009
Dec. 31, 2010
October 2009 Private Placement
Warrants Issued October 2009
Dec. 31, 2011
October 2009 Private Placement
Warrants Issued October 2009
Oct. 16, 2009
October 2009 Private Placement
Warrants Issued October 2009
Mar. 31, 2011
October 2009 Private Placement
Warrants Issued October 2009
Maximum
Oct. 16, 2009
October 2009 Private Placement
Warrants Issued October 2009
American Depositary Share
Mar. 31, 2012
October 2009 Private Placement
Warrants Issued October 2009
Warrant Issued to Employees
Mar. 31, 2011
October 2009 Private Placement
Warrants Issued October 2009
Warrant Issued to Employees
Oct. 16, 2009
October 2009 Private Placement
Warrants Issued October 2009
Bridge Loan
Derivative [Line Items]                                          
Common stock issued under private placement, value     $ 98,671,000           $ 70,000,000                        
Common stock issued under private placement, net proceeds                 62,300,000                        
Bridge notes converted in conjunction with the private placement, amount                   3,600,000                      
Common stock issued under private placement, shares 13,800,000               66,400,000 4,000,000                      
Number of shares that each ADS represents                 1 1                      
Common stock issued under private placement, price per share $ 7.60               $ 1.00                        
Warrant term                                   5 years     5 years
Warrants issued, number of shares called by the warrant                                 18,700,000 0.5     0.5
Exercise price of the warrants   1.48                               1.50     1.50
Bridge notes converted in conjunction with the private placement, shares of common stock issued                   3,999,996                      
Bridge notes converted in conjunction with the private placement, price per share                     $ 0.90                    
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 issued 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.              
Fair value of derivative liability   191,387,000   123,125,000 191,387,000 174,819,000 123,125,000 230,069,000       191,400,000     123,100,000            
Warrants exercised, number of warrants                       40,000 3,900,000                
Warrants exercised, gross proceeds   59,000 6,454,000                 100,000 5,900,000                
Fair value of the warrant derivative liability reclassified from liabilities to equity   321,000 29,229,000                 300,000 29,200,000                
(Gain) loss on change in fair value of derivative liability   (66,209,000) 25,342,000   66,209,000 (25,342,000)           (66,200,000) (25,300,000)                
Compensation (income) expense   $ 3,874,000 $ 1,540,000   $ (2,374,000) $ 679,000                         $ 2,400,000 $ (700,000)