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Derivative Financial Instruments - Changes in Fair Value Inputs and Assumptions (Detail) (Compound Embedded Derivative [Member], USD $)
6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Compound Embedded Derivative [Member]
   
Derivative [Line Items]    
Beginning balance $ 1,529,583 $ 2,680,133
Issuances   1,291,298
Expirations from redemptions of host contracts reflected in income (633,351)  
Changes in fair value inputs and assumptions reflected in income (42,268) 1,227,451
Ending balance $ (853,964) $ 5,198,882