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Basis of Presentation - Additional Information (Detail) (USD $)
Jun. 30, 2012
Dec. 31, 2011
Jun. 30, 2011
Dec. 31, 2010
Basis of Presentation [Line Items]        
Unrestricted cash and cash equivalents $ 5,721,339 $ 6,731,487 $ 7,274,395 $ 10,980,420