Schedule of Investments (Unaudited) - Treasury Bills and Money Market Fund - USD ($)		9 Months Ended		12 Months Ended
		Sep. 30, 2018		Dec. 31, 2017
Schedule Of Investments [Line Items]
Investments in Securities, cost		$ 229,613,206		$ 283,534,397
Percentage of Shareholders' Equity		120.86%		90.26%
Value		$ 207,041,069		$ 244,408,079
Affiliated investments, at value		22,546,692		39,094,237
Total Investments in Securities		229,587,761		283,502,316
Affiliated Investments [Member]
Schedule Of Investments [Line Items]
Affiliated Investments, at Cost		$ 22,535,208		$ 39,110,095
Percentage of Shareholders' Equity		11.87%		12.45%
Affiliated investments, at value		$ 22,546,692		$ 39,094,237
U.S. Treasury Bills, 2.010% due November 8, 2018 [Member]
Schedule Of Investments [Line Items]
Investment Interest Rate	[1]	2.01%
Investment Maturity Date	[1]	Nov. 08, 2018
Percentage of Shareholders' Equity	[1]	39.40%
Value	[1]	$ 74,836,521
Principal Value	[1]	$ 75,000,000
U.S. Treasury Bills, 2.095% due December 6, 2018 [Member]
Schedule Of Investments [Line Items]
Investment Interest Rate	[1],[2]	2.095%
Investment Maturity Date	[1],[2]	Dec. 06, 2018
Restricted for maintenance margin	[1],[2]	$ 83,844,045
Percentage of Shareholders' Equity	[1],[2]	25.69%
Value	[1],[2]	$ 48,809,329
Principal Value	[1],[2]	$ 49,000,000
U.S. Treasury Bills, 2.175% due January 3, 2019 [Member]
Schedule Of Investments [Line Items]
Investment Interest Rate	[1],[2]	2.175%
Investment Maturity Date	[1],[2]	Jan. 03, 2019
Restricted for maintenance margin		$ 83,844,045
Percentage of Shareholders' Equity	[1],[2]	26.69%
Value	[1],[2]	$ 50,708,032
Principal Value	[1],[2]	$ 51,000,000
U.S. Treasury Bills, 2.210% due February 28, 2019 [Member]
Schedule Of Investments [Line Items]
Investment Interest Rate	[1],[2]	2.21%
Investment Maturity Date	[1],[2]	Feb. 28, 2019
Restricted for maintenance margin		$ 83,844,045
Percentage of Shareholders' Equity	[1],[2]	17.21%
Value	[1],[2]	$ 32,687,187
Principal Value	[1],[2]	33,000,000
United States Treasury Obligations [Member]
Schedule Of Investments [Line Items]
Investments in Securities, cost	[1]	$ 207,077,998		$ 244,424,302
Percentage of Shareholders' Equity	[1]	108.99%		77.81%
Value	[1]	$ 207,041,069		$ 244,408,079
Exchange-Traded Fund [Member] | Affiliated Investments [Member]
Schedule Of Investments [Line Items]
Affiliated Investments, at Cost	[3]	$ 16,006,371		$ 16,006,371
Percentage of Shareholders' Equity	[3]	8.43%		5.09%
Affiliated investments, at value	[3]	$ 16,017,855		$ 15,990,513
Shares	[3]	151,900		151,900
Money Market Mutual Fund - Premier U.S. Government Money Portfolio - Institutional Class [Member] | Affiliated Investments [Member]
Schedule Of Investments [Line Items]
Investment Interest Rate		1.95%	[4]	1.15%	[5]
Affiliated Investments, at Cost		$ 6,528,837	[4]	$ 23,103,724	[5]
Percentage of Shareholders' Equity		3.44%	[4]	7.36%	[5]
Affiliated investments, at value		$ 6,528,837	[4]	$ 23,103,724	[5]
Shares		6,528,837	[4]	23,103,724	[5]
A L P S Distributors Inc | Affiliated Investments [Member]
Schedule Of Investments [Line Items]
Affiliated Investments, at Cost		$ 22,535,208
U.S. Treasury Bills, 1.180% due January 4, 2018 [Member]
Schedule Of Investments [Line Items]
Investment Interest Rate	[1]			1.18%
Investment Maturity Date	[1]			Jan. 04, 2018
Percentage of Shareholders' Equity	[1]			14.01%
Value	[1]			$ 43,997,241
Principal Value	[1]			$ 44,000,000
U.S. Treasury Bills, 1.285% due March 1, 2018 [Member]
Schedule Of Investments [Line Items]
Investment Interest Rate	[1],[6]			1.285%
Investment Maturity Date	[1],[6]			Mar. 01, 2018
Restricted for maintenance margin	[1],[6]			$ 12,972,700
Percentage of Shareholders' Equity	[1],[6]			13.34%
Value	[1],[6]			$ 41,914,233
Principal Value	[1],[6]			$ 42,000,000
U.S. Treasury Bills, 1.245% due January 18, 2018 [Member]
Schedule Of Investments [Line Items]
Investment Interest Rate	[1]			1.245%
Investment Maturity Date	[1]			Jan. 18, 2018
Percentage of Shareholders' Equity	[1]			14.95%
Value	[1]			$ 46,974,228
Principal Value	[1]			$ 47,000,000
U.S. Treasury Bills, 1.285% due February 22, 2018 [Member]
Schedule Of Investments [Line Items]
Investment Interest Rate	[1]			1.285%
Investment Maturity Date	[1]			Feb. 22, 2018
Percentage of Shareholders' Equity	[1]			16.21%
Value	[1]			$ 50,908,965
Principal Value	[1]			$ 51,000,000
U.S. Treasury Bills, 1.450% due June 7, 2018 [Member]
Schedule Of Investments [Line Items]
Investment Interest Rate	[1]			1.45%
Investment Maturity Date	[1]			Jun. 07, 2018
Percentage of Shareholders' Equity	[1]			19.30%
Value	[1]			$ 60,613,412
Principal Value	[1]			$ 61,000,000

[1] Security may be traded on a discount basis. The interest rate shown represents the discount rate at the most recent auction date of the security prior to period end.

[2] United States Treasury Obligations of $83,844,045 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.

[3] Affiliated company. The security and the Fund are affiliated by having the same investment adviser. See Note 8.

[4] The security and the Fund are advised by wholly-owned subsidiaries of Invesco Ltd. and are therefore considered to be affiliated. The rate shown is the 7-day SEC standardized yield as of September 30, 2018.

[5] The security and the Fund are advised by wholly-owned subsidiaries of Invesco Ltd. and are therefore considered to be affiliated. The rate shown is the 7-day SEC standardized yield as of December 31, 2017.

[6] United States Treasury Obligations of $12,972,700 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.