Schedule of Investments (Unaudited) - Treasury Bills and Money Market Fund - USD ($)		3 Months Ended		12 Months Ended
		Mar. 31, 2019		Dec. 31, 2018
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity		100.15%		101.06%
United States Treasury Obligations, Value		$ 30,909,645		$ 27,887,293
Affiliated investments, value		2,271,254		1,793,677
Investments in Securities, Value		33,180,899		29,680,970
Investments in Securities, cost		$ 33,179,572		$ 29,680,281
U.S. Treasury Bills, 2.465% due April 4, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	18.11%		20.30%
United States Treasury Obligations, Value	[1]	$ 5,998,822		$ 5,962,874
United States Treasury Obligations, Principal Value	[1]	$ 6,000,000		$ 6,000,000
Investment Interest Rate	[1]	2.465%		2.465%
Investment Maturity Date	[1]	Apr. 04, 2019		Apr. 04, 2019
U.S. Treasury Bills, 2.470% due April 23, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	15.07%
United States Treasury Obligations, Value	[1]	$ 4,992,715
United States Treasury Obligations, Principal Value	[1]	$ 5,000,000
Investment Interest Rate	[1]	2.47%
Investment Maturity Date	[1]	Apr. 23, 2019
U.S. Treasury Bills,2.375% due May 2, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	33.13%
United States Treasury Obligations, Value	[1],[2]	$ 10,977,799
United States Treasury Obligations, Principal Value	[1],[2]	$ 11,000,000
Investment Interest Rate	[1],[2]	2.375%
Investment Maturity Date	[1],[2]	May 02, 2019
Restricted for maintenance margin		$ 1,606,619
U.S. Treasury Bills, 2.470% due July 11, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	26.99%
United States Treasury Obligations, Value	[1]	$ 8,940,309
United States Treasury Obligations, Principal Value	[1]	$ 9,000,000
Investment Interest Rate	[1]	2.47%
Investment Maturity Date	[1]	Jul. 11, 2019
United States Treasury Obligations [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	93.30%		94.95%
United States Treasury Obligations, Value	[1]	$ 30,909,645		$ 27,887,293
Investments in Securities, cost	[1]	$ 30,908,318		$ 27,886,604
Money Market Mutual Fund - Invesco Premier U.S. Government Money Portfolio - Institutional Class [Member] | Affiliated Investments [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity		6.85%	[3]	6.11%	[4]
Affiliated investments, value		$ 2,271,254	[3]	$ 1,793,677	[4]
Shares		2,271,254	[3]	1,793,677	[4]
Investment Interest Rate		2.33%	[3]	2.30%	[4]
Investments in Securities, cost		$ 2,271,254	[3]	$ 1,793,677	[4]
U.S. Treasury Bills, 2.175% due January 3, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]			34.05%
United States Treasury Obligations, Value	[1]			$ 9,999,377
United States Treasury Obligations, Principal Value	[1]			$ 10,000,000
Investment Interest Rate	[1]			2.175%
Investment Maturity Date	[1]			Jan. 03, 2019
U.S. Treasury Bills, 2.370% due February 28, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]			16.96%
United States Treasury Obligations, Value	[1]			$ 4,981,188
United States Treasury Obligations, Principal Value	[1]			$ 5,000,000
Investment Interest Rate	[1]			2.37%
Investment Maturity Date	[1]			Feb. 28, 2019
U.S. Treasury Bills, 2.430% due May 2, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[5]			23.64%
United States Treasury Obligations, Value	[1],[5]			$ 6,943,854
United States Treasury Obligations, Principal Value	[1],[5]			$ 7,000,000
Investment Interest Rate	[1],[5]			2.43%
Investment Maturity Date	[1],[5]			May 02, 2019
Restricted for maintenance margin				$ 605,120

[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 $1,606,619 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.

[3] 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 March 31, 2019.

[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 December 31, 2018.

[5] United States Treasury Obligations of $605,120 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.