Schedule of Investments (Unaudited) - Futures Contracts		9 Months Ended	12 Months Ended
		Sep. 30, 2018 USD ($) Contract	Dec. 31, 2017 USD ($) Contract
Schedule Of Investments [Line Items]
Value		$ 229,587,761	$ 283,502,316
Futures [Member] | Long [Member]
Schedule Of Investments [Line Items]
Value	[1]	(19,773,575)	31,489,170
Unrealized Appreciation (Depreciation)	[1]	$ (19,773,575)	$ 31,489,170
Futures [Member] | Long [Member] | LME CLEAR [Member] | Aluminum [Member]
Schedule Of Investments [Line Items]
Number of Contracts | Contract		1,288	1,860
Expiration Date		Oct. 31, 2019	Oct. 31, 2018
Notional Value		$ 67,821,250	$ 106,903,500
Value	[1]	353,581	6,848,032
Unrealized Appreciation (Depreciation)	[1]	$ 353,581	$ 6,848,032
Futures [Member] | Long [Member] | LME CLEAR [Member] | Copper [Member]
Schedule Of Investments [Line Items]
Number of Contracts | Contract		407	583
Expiration Date		Feb. 28, 2019	Feb. 28, 2018
Notional Value		$ 63,700,588	$ 105,442,838
Value	[1]	(8,575,437)	20,057,969
Unrealized Appreciation (Depreciation)	[1]	$ (8,575,437)	$ 20,057,969
Futures [Member] | Long [Member] | LME CLEAR [Member] | Zinc [Member]
Schedule Of Investments [Line Items]
Number of Contracts | Contract		896	1,265
Expiration Date		Jan. 31, 2019	Jan. 31, 2019
Notional Value		$ 58,396,800	$ 101,832,500
Value	[1]	(11,551,719)	4,583,169
Unrealized Appreciation (Depreciation)	[1]	$ (11,551,719)	$ 4,583,169

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