Statements of Operations - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investment Income
Interest		$ 24,497,221	$ 9,707,419	$ 2,294,340
Total investment income		24,497,221	9,707,419	2,294,340
Expenses
Sponsor’s fees		10,502,114	8,530,039	6,359,820
Brokerage commissions and fees		1,422,790	1,337,872	1,036,318
Total expenses		11,924,904	9,867,911	7,396,138
Net investment income (loss)		12,572,317	(160,492)	(5,101,798)
Net Realized and Unrealized Gain (Loss)
Short-term investments		3,343	2,812	50,156
Futures contracts		(11,940,106)	3,410,884	76,363,644
Net realized gain (loss)		(11,936,763)	3,413,696	76,413,800
Net change in unrealized appreciation/depreciation on:
Short-term investments		77,730	(59,334)	20,363
Futures contracts		(190,921,734)	77,224,746	12,329,480
Net change in unrealized appreciation/depreciation		(190,844,004)	77,165,412	12,349,843
Net realized and unrealized gain (loss)		(202,780,767)	80,579,108	88,763,643
Net increase (decrease) in net assets resulting from operations		$ (190,208,450)	$ 80,418,616	$ 83,661,845
Net increase (decrease) in net assets per Share(a) (in dollars per share)	[1]	$ (2.29)	$ 1.05	$ 1.43

[1] Net increase (decrease) in net assets per Share based on average shares outstanding during the period.