Schedule of Investments - Futures Contracts		12 Months Ended
		Dec. 31, 2017 USD ($) Contract		Dec. 31, 2016 USD ($) Contract
Schedule of Investments [Line Items]
Value		$ 541,184,203		$ 849,945,124
Futures [Member] | United States of America, Dollars [Member] | ICE FUTURES U.S. [Member] | Long [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		5,801		8,270
Expiration Date		Mar. 31, 2018		Mar. 31, 2017
Notional Value		$ 532,682,626		$ 845,905,220
Value	[1]	(7,972,637)
Unrealized Appreciation (Depreciation)		$ (7,972,637)	[1]	$ 1,988,810	[2]

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

[2] Unrealized Appreciation (Depreciation) is presented above, net by contract.