Schedule of Investments (Unaudited) - Futures Contracts		3 Months Ended	12 Months Ended
		Mar. 31, 2018 USD ($) Contract	Dec. 31, 2017 USD ($) Contract
Schedule of Investments [Line Items]
Value		$ 500,601,342	$ 541,184,203
Futures [Member] | United States of America, Dollars [Member] | Long [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		5,575	5,801
Expiration Date		Jun. 30, 2018	Mar. 31, 2018
Notional Value		$ 500,701,900	$ 532,682,626
Value	[1]	2,298,198	(7,972,637)
Unrealized Appreciation (Depreciation)	[1]	$ 2,298,198	$ (7,972,637)

[1] Unrealized Appreciation (Depreciation) and Value are presented above, net by contract.