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Significant Accounting Policies - Additional Information (Detail) (USD $)
 3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Mar. 31, 2012
Dec. 31, 2011
Year
Mar. 31, 2011
Dec. 31, 2010
Significant Accounting Policies [Line Items]                
Fair value of derivative liability $ 120,214,000   $ 120,214,000     $ 123,125,000    
Warrant derivative liability fair value assumptions, risk-free rate     0.35%          
Warrant derivative liability fair value assumptions, remaining term     2 years 3 months 18 days          
Warrant derivative liability fair value assumptions, volatility rate     97.00%          
Loss (Gain) on change in fair value of derivative liability (18,930,000) (185,359,000) (85,139,000) (160,017,000)        
Compensation expense for change in fair value of warrants issued to former employees     (8,709,000) (3,360,000)        
Market price of stock $ 14.46   $ 14.46          
Scenario 4
                
Significant Accounting Policies [Line Items]                
Hypothetical increase in the market price     10.00%          
Market price of stock $ 15.91   $ 15.91          
Increase (decrease) in the fair value of the warrant derivative liability     13,200,000          
Warrants Issued October 2009
                
Significant Accounting Policies [Line Items]                
Fair value of derivative liability 120,214,000 285,984,000 120,214,000 285,984,000 191,387,000 123,125,000 174,819,000 230,069,000
Warrant derivative liability valuation assumptions, risk-free rate           0.36%    
Warrant derivative liability valuation assumptions, remaining term           2.8    
Warrant derivative liability valuation assumptions, volatility rate           118.00%    
Increase (Decrease) in the fair value of warrant derivative liability     2,900,000          
Transfers to equity 91,961,000 79,229,000 92,282,000 108,458,000        
Loss (Gain) on change in fair value of derivative liability 18,930,000 185,359,000 85,139,000 160,017,000        
Compensation expense for change in fair value of warrants issued to former employees $ 1,858,000   $ 4,232,000          
Maximum
                
Significant Accounting Policies [Line Items]                
Short term highly liquid instruments, maturity date     90 days