Condensed Schedule of Investments (Parenthetical) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Cost of investments in U.S. government securities	$ 25,039,569	$ 34,975,633
Options purchased at cost	147,400	577,300
Premium received	157,300	635,950
United States Government Treasury Bills [Member]
Schedule of Investments [Line Items]
Cost of investments in U.S. government securities	$ 25,039,569	$ 34,975,633
United States Government Treasury Bills [Member] \| Treasury Bill 0% due March 8, 2018 [Member]
Schedule of Investments [Line Items]
Investment, Maturity date	Mar. 08, 2018
Investment, Interest rate	0.00%
United States Government Treasury Bills [Member] \| Treasury Bill 0% due February 22, 2018 [Member]
Schedule of Investments [Line Items]
Investment, Maturity date	Feb. 22, 2018
Investment, Interest rate	0.00%
United States Government Treasury Bills [Member] \| Treasury Bill 0% due February 1, 2018 [Member]
Schedule of Investments [Line Items]
Investment, Maturity date	Feb. 01, 2018
Investment, Interest rate	0.00%
United States Government Treasury Bills [Member] \| Treasury Bill 0% due January 4, 2018 [Member]
Schedule of Investments [Line Items]
Investment, Maturity date	Jan. 04, 2018
Investment, Interest rate	0.00%
United States Government Treasury Bills [Member] \| Treasury Bill 0% due May 4, 2017 [Member]
Schedule of Investments [Line Items]
Investment, Maturity date		May 04, 2017
Investment, Interest rate		0.00%
United States Government Treasury Bills [Member] \| Treasury Bill 0% due April 6, 2017 [Member]
Schedule of Investments [Line Items]
Investment, Maturity date		Apr. 06, 2017
Investment, Interest rate		0.00%
United States Government Treasury Bills [Member] \| Treasury Bill 0% due March 2, 2017 [Member]
Schedule of Investments [Line Items]
Investment, Maturity date		Mar. 02, 2017
Investment, Interest rate		0.00%
United States Government Treasury Bills [Member] \| Treasury Bill 0% due February 2, 2017 [Member]
Schedule of Investments [Line Items]
Investment, Maturity date		Feb. 02, 2017
Investment, Interest rate		0.00%

Options purchased at cost.

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- Definition

The interest rate for investments that have an interest rate. For fixed rate investments, this indicates the fixed interest rate. If the investment has a variable interest rate, the rate stated here may be the rate that is currently relevant. In this case the "Investment, Interest Rate is Current Rate for Variable Rate Investment Flag", "Investment, Interest Rate is Discount Rate at Purchase Flag", "Investment, Interest Rate Reflects Current Yield Flag" should be used. If one of these flags are not appropriate to explain the interest rate that is indicated, then a new flag should be added or an explanation should be included in "Investment, Additional Information".

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

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- Definition

The maturity date of the investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

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- Definition

Cost of the investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=63488139&loc=d3e12121-115841

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- Definition

Represents the premiums earned on the open option contracts held by the fund. This item is not required to be disclosed in Regulation S-X but is commonly reported by some funds.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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