Schedule of Investments (Unaudited) - Treasury Bills and Money Market Fund - USD ($) | 3 Months Ended | 12 Months Ended |
Mar. 31, 2018 | Dec. 31, 2017 |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | | 99.96% | | 101.59% | |
Value | | $ 403,014,990 | | $ 460,172,505 | |
Affiliated Investments, at value | | 97,586,352 | | 81,011,698 | |
Total Investments in Securities | | 500,601,342 | | 541,184,203 | |
Investments in Securities, cost | | $ 500,717,746 | | $ 541,547,464 | |
Affiliated Investments [Member] | | | | | |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | | 19.49% | | 15.21% | |
Affiliated Investments, at value | | $ 97,586,352 | | $ 81,011,698 | |
Affiliated Investments, at Cost | | $ 97,593,316 | | $ 81,329,032 | |
U.S. Treasury Bills, 1.695% due May 3, 2018 [Member] | | | | | |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | [1] | 8.77% | | | |
Value | [1] | $ 43,938,593 | | | |
Principal Value | [1] | $ 44,000,000 | | | |
Investment Interest Rate | [1] | 1.695% | | | |
Investment Maturity Date | [1] | May 3, 2018 | | | |
U.S. Treasury Bills, 1.660% due June 7, 2018 [Member] | | | | | |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | [1] | 15.73% | | | |
Value | [1] | $ 78,760,045 | | | |
Principal Value | [1] | $ 79,000,000 | | | |
Investment Interest Rate | [1] | 1.66% | | | |
Investment Maturity Date | [1] | Jun. 7, 2018 | | | |
U.S. Treasury Bills, 1.740% due July 5, 2018 [Member] | | | | | |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | [1],[2] | 30.21% | | | |
Value | [1],[2] | $ 151,323,167 | | | |
Principal Value | [1],[2] | $ 152,000,000 | | | |
Investment Interest Rate | [1],[2] | 1.74% | | | |
Investment Maturity Date | [1],[2] | Jul. 5, 2018 | | | |
Restricted for maintenance margin | | $ 19,910,000 | | | |
U.S. Treasury Bills, 1.830% due August 30, 2018 [Member] | | | | | |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | [1] | 25.76% | | | |
Value | [1] | $ 128,993,185 | | | |
Principal Value | [1] | $ 130,000,000 | | | |
Investment Interest Rate | [1] | 1.83% | | | |
Investment Maturity Date | [1] | Aug. 30, 2018 | | | |
United States Treasury Obligations [Member] | | | | | |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | [1] | 80.47% | | 86.38% | |
Value | [1] | $ 403,014,990 | | $ 460,172,505 | |
Investments in Securities, cost | [1] | $ 403,124,430 | | $ 460,218,432 | |
Exchange-Traded Fund - PowerShares Treasury Collateral Portfolio [Member] | Affiliated Investments [Member] | | | | | |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | [3] | 15.98% | | 14.96% | |
Affiliated Investments, at value | [3] | $ 79,999,760 | | $ 79,689,390 | |
Shares | [3] | 757,000 | | 757,000 | |
Affiliated Investments, at Cost | [3] | $ 80,006,724 | | $ 80,006,724 | |
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 | | 3.51% | [4] | 0.25% | [5] |
Affiliated Investments, at value | | $ 17,586,592 | [4] | $ 1,322,308 | [5] |
Shares | | 17,586,592 | [4] | 1,322,308 | [5] |
Investment Interest Rate | | 1.52% | [4] | 1.15% | [5] |
Investments in Securities, cost | | $ 17,586,592 | [4] | $ 1,322,308 | [5] |
U.S. Treasury Bills, 1.180% due January 4, 2018 [Member] | | | | | |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | [1] | | | 35.10% | |
Value | [1] | | | $ 186,988,273 | |
Principal Value | [1] | | | $ 187,000,000 | |
Investment Interest Rate | [1] | | | 1.18% | |
Investment Maturity Date | [1] | | | Jan. 4, 2018 | |
U.S. Treasury Bills, 1.245% due January 18, 2018 [Member] | | | | | |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | [1] | | | 4.50% | |
Value | [1] | | | $ 23,986,840 | |
Principal Value | [1] | | | $ 24,000,000 | |
Investment Interest Rate | [1] | | | 1.245% | |
Investment Maturity Date | [1] | | | Jan. 18, 2018 | |
U.S. Treasury Bills, 1.285% due March 1, 2018 [Member] | | | | | |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | [1],[6] | | | 34.10% | |
Value | [1],[6] | | | $ 181,628,342 | |
Principal Value | [1],[6] | | | $ 182,000,000 | |
Investment Interest Rate | [1],[6] | | | 1.285% | |
Investment Maturity Date | [1],[6] | | | Mar. 1, 2018 | |
Restricted for maintenance margin | | | | $ 19,958,000 | |
U.S. Treasury Bills, 1.450% due June 7, 2018 [Member] | | | | | |
Schedule of Investments [Line Items] | | | | | |
Percentage of Shareholders' Equity | [1] | | | 12.68% | |
Value | [1] | | | $ 67,569,050 | |
Principal Value | [1] | | | $ 68,000,000 | |
Investment Interest Rate | [1] | | | 1.45% | |
Investment Maturity Date | [1] | | | Jun. 7, 2018 | |
| |
[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 $19,910,000 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 March 31, 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 $19,958,000 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts. | |