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Fair Value of Financial Instruments (Effect of Derivative Instruments on Condensed Statements of Operations) (Details) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]        
Realized Gain or (Loss) on Derivatives Recognized in Income $ 1,133,470 $ (6,014,750) $ 2,298,660 $ (3,856,050)
Change in Unrealized Gain or (Loss) on Derivatives Recognized in Income     (1,111,600) (12,464,380)
Commodity Contracts [Member] | Futures [Member] | Realized gain on closed positions [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Realized Gain or (Loss) on Derivatives Recognized in Income     2,298,660 (3,856,050)
Commodity Contracts [Member] | Futures [Member] | Change in unrealized gain (loss) on open positions [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Change in Unrealized Gain or (Loss) on Derivatives Recognized in Income     $ (1,111,600) $ (12,464,380)