Statements Of Income And Expenses (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Income
Interest Income	$ 396,017	$ 303,911	$ 834,901	$ 2,004,164
Expenses
Management Fee	4,303,084	6,422,717	12,383,841	20,990,965
Brokerage Commissions and Fees	301,492	408,982	1,153,576	1,782,401
Total Expenses	4,604,576	6,831,699	13,537,417	22,773,366
Net investment income (loss)	(4,208,559)	(6,527,788)	(12,702,516)	(20,769,202)
Net Realized Gain (Loss) on
United States Treasury Obligations	6,213	12,849	7,181	62,390
Futures	34,861,538	(68,820,001)	(265,409,966)	222,584,524
Net realized gain (loss)	34,867,751	(68,807,152)	(265,402,785)	222,646,914
Net Change in Unrealized Gain (Loss) on
United States Treasury Obligations	2,737	(34,449)	43,876	(10,176)
Futures	57,211,788	(118,873,643)	310,890,827	(470,536,617)
Net change in unrealized gain (loss)	57,214,525	(118,908,092)	310,934,703	(470,546,793)
Net realized and net change in unrealized gain (loss) on United States Treasury Obligations and Futures	92,082,276	(187,715,244)	45,531,918	(247,899,879)
Net Income (Loss)	$ 87,873,717	$ (194,243,032)	$ 32,829,402	$ (268,669,081)