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Stock Purchase Warrants (Details) (USD $)
 3 Months Ended 288 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Mar. 31, 2013
Mar. 31, 2013
January 2010 Class A Warrants
Dec. 31, 2012
January 2010 Class A Warrants
Mar. 31, 2013
December 2010 Warrants
Dec. 31, 2012
December 2010 Warrants
Mar. 31, 2013
October 2007 Warrants
Oct. 17, 2007
October 2007 Warrants
Stock Purchase Warrants                  
Number of warrants issued                 740,131
Exercise price per share (in dollars per share)       $ 2.44   $ 1.25   $ 12.72  
Warrants outstanding       6,034,637   308,100      
Total shares issuable on exercise       4,525,978   308,100      
Assumptions used in calculating the estimated fair value of the warrants                  
Closing stock price (in dollars per share)       $ 0.70 $ 1.26 $ 0.70 $ 1.26    
Expected dividend rate (as a percent)       0.00% 0.00% 0.00% 0.00%    
Expected stock price volatility (as a percent)       59.30% 74.00% 77.90% 70.10%    
Risk-free interest rate (as a percent)       0.30% 0.40% 0.30% 0.40%    
Expected life       2 years 3 months 2 years 6 months 2 years 8 months 16 days 2 years 11 months 16 days    
Change in the estimated fair value of warrant liabilities                  
Balance at the beginning of the period $ 1,995,000                
Decrease in fair value of warrants (1,619,000) 900,000 (18,156,000)            
Balance at the end of the period 376,000   376,000            
Gross proceeds raised from sale of shares under ATM $ 2,451,000