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Summary of Significant Accounting Policies - Stock options' weighted average assumptions and grant date fair values (Details) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Accounting Policies [Abstract]      
Risk-free interest rate (%) 177.00% 330.00% 303.00%
Dividend yield         
Volatility factor 70.00% 60.00% 90.00%
Expected option life (years) 4 years 10 months 26 days 5 years 8 months 14 days 4 years
Weighted average grant date fair value $ 0.98 $ 1.08 $ 1.92