Note 9 - Investing in Index Futures - Effect of the Futures Contracts, by Risk Exposure Category, on the Statements of Financial Condition (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Receivable for variation margin on open futures contracts (Note 9)	$ 920,643	$ 5,558,077
Commodity Contract [Member] \| Receivable for Variation Margin on Open Futures Contracts [Member]
Receivable for variation margin on open futures contracts (Note 9)	920,643	5,558,077
Commodity Contract [Member] \| Payable for Variation Margin on Open Futures Contracts [Member]
Payable for variation margin on open futures contracts	$ 0	$ 0

Amount receivable from broker-dealers and clearing organizations, including, but not limited to, securities failed-to-deliver, certain deposits for securities borrowed, open transactions, good faith and margin deposits, commissions and floor brokerage receivables.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=35710130&loc=d3e41645-110958

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant