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Fair Value Measurement of Assets And Liabilities (Details 2) (USD $)
Mar. 31, 2012
Dec. 31, 2011
Estimated fair values of short-term and long-term investments    
One year or less $ 5,681,957  
One year to two years 2,184,022  
Two years to three years 14,481,405  
Three years to four years 10,572,742  
Four years to five years 5,521,910  
More than five years 10,324,394  
Total $ 48,766,430 $ 46,842,210