Note 9 - Investing in Index Futures (Details) - Effect of the Futures Contracts, by Risk Exposure Category, on the Statements of Assets and Liabilities - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Receivable for variation margin on open futures contracts	$ 6,562,418	$ 0	[1]
Payable for variation margin on open futures contracts	0	7,717,674	[1]
Commodity Contract [Member] | Rеcеivablе for Variation Margin on Opеn Futurеs Contracts [Member]
Derivatives, Fair Value [Line Items]
Receivable for variation margin on open futures contracts	$ 6,562,418
Commodity Contract [Member] | Payable for Variation Margin on Open Futures Contracts [Member]
Derivatives, Fair Value [Line Items]
Payable for variation margin on open futures contracts		$ 7,717,674

[1] Previously reported as "Statements of Financial Condition." Please refer to Note 2A.