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Stock Purchase Warrants (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
 3 Months Ended 9 Months Ended 282 Months Ended 9 Months Ended 12 Months Ended 1 Months Ended 9 Months Ended 12 Months Ended 1 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Dec. 31, 2011
Sep. 30, 2012
Warrant exchange offer
Sep. 30, 2012
October 2007 Warrants
Dec. 31, 2011
October 2007 Warrants
Oct. 17, 2007
October 2007 Warrants
Jan. 31, 2010
January 2010 Class A Warrants
Sep. 30, 2012
January 2010 Class A Warrants
Jan. 21, 2010
January 2010 Class A Warrants
Sep. 30, 2012
January 2010 Class A Warrants
Level 3
Dec. 31, 2011
January 2010 Class A Warrants
Level 3
Dec. 31, 2010
December 2010 Warrants
Sep. 30, 2012
December 2010 Warrants
Dec. 15, 2010
December 2010 Warrants
Jul. 27, 2012
December 2010 Warrants
Warrant exchange offer
Sep. 30, 2012
December 2010 Warrants
Level 3
Dec. 31, 2011
December 2010 Warrants
Level 3
Stock Purchase Warrants                                          
Number of warrants issued (in shares)                   740,131     4,882,228         10,000,000      
Exercise price per share (in dollars per share)               $ 12.72       $ 2.48         $ 1.75 $ 3.22      
Exercisable period                     5 years         5 years          
Warrants outstanding             308,100         4,525,978                  
Assumptions used in calculating the estimated fair value of the warrants                                          
Closing stock price (in dollars per share)               $ 1.63 $ 1.82         $ 1.63 $ 1.82         $ 1.63 $ 1.82
Expected dividend rate (as a percent)               0.00% 0.00%         0.00% 0.00%         0.00% 0.00%
Expected stock price volatility (as a percent)               56.20% 93.60%         73.60% 86.10%         70.70% 83.60%
Risk-free interest rate (as a percent)               0.20% 0.10%         0.30% 0.50%         0.40% 0.60%
Expected life               6 months 1 year 3 months         2 years 9 months 3 years 6 months         3 years 2 months 16 days 3 years 11 months 16 days
Change in the estimated fair value of warrant liabilities                                          
Balance at the beginning of the period     $ 16,625                                    
Warrants exchanged for common stock     (10,382)                                    
Decrease in fair value of warrants (2,241) (5,496) (3,289) (4,286) (15,578)                                
Balance at the end of the period $ 2,954   $ 2,954   $ 2,954                                
Common stock issued in exchange of warrants (in shares) 43,784,000   43,784,000   43,784,000 38,635,000                         4,845,949    
Warrants exchanged for shares of common stock                                     9,691,900