Financial Highlights (Per Unit Performance Data and Other Supplemental Financial Data) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2009	Nov. 18, 2009
Per Unit Operating Performance:
Net asset value, beginning of period	$ 17.23	$ 21.21	$ 35.02	$ 35.02	$ 50.00
Total income (loss)	$ 1.32	$ (3.78)	$ (13.42)
Net expenses	$ (0.23)	$ (0.20)	$ (0.39)
Net decrease in net asset value	$ 1.09	$ (3.98)	$ (13.81)
Net asset value, end of period	$ 18.32	$ 17.23	$ 21.21	$ 35.02	$ 50.00
Total Return	6.33%	(18.76%)	(39.43%)
Ratios to Average Net Assets
Total income (loss)	13.23%	(11.80%)	(44.03%)
Management fees	0.75%	0.75%	0.75%
Total expenses excluding management fees	0.51%	0.40%	0.53%
Expenses waived	(0.30%)	(0.18%)	(0.36%)
Net expenses excluding management fees	0.21%	0.22%	0.17%
Net income (loss)	12.27%	(12.77%)	(44.95%)