Financial Instruments (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Investment Holdings [Line Items]
Net unrealized gain/(loss) on open contracts	$ 177,506	$ 2,551,354
Cash held by acting commodity futures brokers administrating open contracts	159,234,167	200,859,877
Exchange-Traded [Member]
Investment Holdings [Line Items]
Net unrealized gain/(loss) on open contracts	(157,674)	2,503,274
Longest maturity date	Jun. 30, 2017	Mar. 31, 2017
Off-Exchange-Traded [Member]
Investment Holdings [Line Items]
Net unrealized gain/(loss) on open contracts	$ 335,180	$ 48,080
Longest maturity date	Dec. 31, 2013	Mar. 31, 2013