Note 9 - Investing in Index Futures - Effect of the Futures Contracts, by Risk Exposure Category, on the Statements of Financial Condition (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Receivable for variation margin on open futures contracts	$ 5,954,273	$ 0
Commodity Contract [Member] | Receivable for Variation Margin on Open Futures Contracts [Member]
Receivable for variation margin on open futures contracts	5,954,273	0
Commodity Contract [Member] | Payable for Variation Margin on Open Futures Contracts [Member]
Payable for variation margin on open futures contracts	$ 0	$ 5,952,581