Financial Instruments (Details) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Investment Holdings [Line Items]
Net unrealized gains/ (losses) on open contracts	$ (1,975,691)	$ (1,105,501)
Cash held by acting commodity futures brokers administrating open contracts	42,491,342	43,297,414
Exchange-Traded [Member]
Investment Holdings [Line Items]
Net unrealized gains/ (losses) on open contracts	(1,534,184)	(2,010,679)
Longest maturity date	Sep. 30, 2014	Sep. 30, 2014
Off-Exchange-Traded [Member]
Investment Holdings [Line Items]
Net unrealized gains/ (losses) on open contracts	$ (441,507)	$ 905,178
Longest maturity date	Sep. 30, 2013	Mar. 31, 2013