Schedule of Investments - Futures Contracts		12 Months Ended
		Dec. 31, 2017 USD ($) Contract		Dec. 31, 2016 USD ($) Contract
Schedule of Investments [Line Items]
Value		$ 2,156,785,955		$ 2,534,867,828
Long [Member] | Futures [Member]
Schedule of Investments [Line Items]
Value	[1]	115,669,315
Unrealized Appreciation (Depreciation)		$ 115,669,315	[1]	$ 101,032,417	[2]
Long [Member] | Futures [Member] | CME SWAPS MARKETS (CBOT) [Member] | Corn [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		6,533		6,981
Expiration Date		Sep. 30, 2018		Sep. 30, 2017
Notional Value		$ 122,412,087		$ 129,584,812
Value	[1]	(7,940,794)
Unrealized Appreciation (Depreciation)		$ (7,940,794)	[1]	$ 1,268,361	[2]
Long [Member] | Futures [Member] | CME SWAPS MARKETS (CBOT) [Member] | Soybean [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		2,491		2,697
Expiration Date		Nov. 30, 2018		Nov. 30, 2017
Notional Value		$ 121,529,663		$ 133,400,362
Value	[1]	(1,887,221)
Unrealized Appreciation (Depreciation)		$ (1,887,221)	[1]	$ 3,209,119	[2]
Long [Member] | Futures [Member] | CME SWAPS MARKETS (CBOT) [Member] | Wheat [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		5,355		5,783
Expiration Date		Jul. 31, 2018		Jul. 31, 2017
Notional Value		$ 121,357,688		$ 125,563,388
Value	[1]	(11,431,220)
Unrealized Appreciation (Depreciation)		$ (11,431,220)	[1]	$ (29,220,100)	[2]
Long [Member] | Futures [Member] | CME SWAPS MARKETS (COMEX) [Member] | Gold [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		1,374		1,480
Expiration Date		Aug. 31, 2018		Aug. 31, 2017
Notional Value		$ 181,835,160		$ 171,665,200
Value	[1]	9,038,964
Unrealized Appreciation (Depreciation)		$ 9,038,964	[1]	$ (28,677,888)	[2]
Long [Member] | Futures [Member] | CME SWAPS MARKETS (COMEX) [Member] | Silver [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		509		516
Expiration Date		Dec. 31, 2018		Mar. 31, 2017
Notional Value		$ 44,463,695		$ 41,251,620
Value	[1]	57,475
Unrealized Appreciation (Depreciation)		$ 57,475	[1]	$ (2,503,196)	[2]
Long [Member] | Futures [Member] | ICE FUTURES EUROPE [Member] | Brent Crude Oil [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		4,539		5,706
Expiration Date		Nov. 30, 2018		Oct. 31, 2017
Notional Value		$ 287,409,480		$ 335,113,380
Value	[1]	14,377,382
Unrealized Appreciation (Depreciation)		$ 14,377,382	[1]	$ 19,155,785	[2]
Long [Member] | Futures [Member] | LME CLEAR [Member] | Aluminum [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		1,733		2,266
Expiration Date		Oct. 31, 2018		Oct. 31, 2017
Notional Value		$ 99,604,175		$ 96,630,738
Value	[1]	5,873,854
Unrealized Appreciation (Depreciation)		$ 5,873,854	[1]	$ (551,306)	[2]
Long [Member] | Futures [Member] | LME CLEAR [Member] | Copper [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		542		758
Expiration Date		Feb. 28, 2018		Feb. 28, 2017
Notional Value		$ 98,027,475		$ 104,798,238
Value	[1]	17,219,294
Unrealized Appreciation (Depreciation)		$ 17,219,294	[1]	$ 13,883,069	[2]
Long [Member] | Futures [Member] | LME CLEAR [Member] | Zinc [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		1,177		1,600
Expiration Date		Jan. 31, 2019		Dec. 31, 2017
Notional Value		$ 94,748,500		$ 102,650,000
Value	[1]	4,384,862
Unrealized Appreciation (Depreciation)		$ 4,384,862	[1]	$ 3,269,739	[2]
Long [Member] | Futures [Member] | ICE FUTURES U.S. [Member] | Sugar [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		7,357		5,985
Expiration Date		Sep. 30, 2018		Sep. 30, 2017
Notional Value		$ 125,327,966		$ 125,014,680
Value	[1]	(989,673)
Unrealized Appreciation (Depreciation)		$ (989,673)	[1]	$ (6,328,919)	[2]
Long [Member] | Futures [Member] | CME SWAPS MARKETS (NYMEX) [Member] | Natural Gas [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		4,163		4,517
Expiration Date		Apr. 30, 2018		Aug. 31, 2017
Notional Value		$ 114,107,830		$ 160,443,840
Value	[1]	(4,077,204)
Unrealized Appreciation (Depreciation)		$ (4,077,204)	[1]	$ 20,938,774	[2]
Long [Member] | Futures [Member] | CME SWAPS MARKETS (NYMEX) [Member] | NY Harbor ULSD [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		3,478		4,666
Expiration Date		May 31, 2018		May 31, 2017
Notional Value		$ 288,967,543		$ 342,794,222
Value	[1]	56,451,379
Unrealized Appreciation (Depreciation)		$ 56,451,379	[1]	$ 31,579,715	[2]
Long [Member] | Futures [Member] | CME SWAPS MARKETS (NYMEX) [Member] | RBOB Gasoline [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		3,785		5,079
Expiration Date		Dec. 31, 2018		Nov. 30, 2017
Notional Value		$ 271,218,717		$ 344,999,201
Value	[1]	9,759,527
Unrealized Appreciation (Depreciation)		$ 9,759,527	[1]	$ 13,225,172	[2]
Long [Member] | Futures [Member] | CME SWAPS MARKETS (NYMEX) [Member] | WTI Crude Oil [Member]
Schedule of Investments [Line Items]
Number of Contracts | Contract		4,819		6,278
Expiration Date		Feb. 28, 2018		Feb. 28, 2017
Notional Value		$ 291,260,360		$ 343,155,480
Value	[1]	24,832,690
Unrealized Appreciation (Depreciation)		$ 24,832,690	[1]	$ 61,784,092	[2]

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

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