Schedules of Investments (Unaudited) (Details) - Open S&P GSCI ER Index Futures Contracts - Futures [Member]	9 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Number of contracts	29,515	25,010
Expiration date	December 2015	March 2015
Current notional amount	$ 744,087,908	$ 785,521,583
Net unrealized depreciation	$ (16,884,863)	$ (69,368,696)