Note 9 - Investing in Index Futures (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]

	Asset Derivatives	Fair Value		Liability Derivatives	Fair Value
December 31, 2018
Commodity contracts	Receivable for variation margin on open futures contracts	$	920,643	Payable for variation margin on open futures contracts	$	—
December 31, 2017
Commodity contracts	Receivable for variation margin on open futures contracts	$	5,558,077	Payable for variation margin on open futures contracts	$	—

Derivative Instruments, Gain (Loss) [Table Text Block]

	Statements of Operations Location	Net Realized Gain (Loss)			Net Change in Unrealized Appreciation/Depreciation
December 31, 2018
Commodity contracts	Net realized gain (loss) from futures contracts	$	(11,940,106	)	$	—
	Net change in unrealized appreciation/depreciation on futures contracts		—			(190,921,734	)
December 31, 2017
Commodity contracts	Net realized gain (loss) from futures contracts	$	3,410,884		$	—
	Net change in unrealized appreciation/depreciation on futures contracts		—			77,224,746
December 31, 201 6
Commodity contracts	Net realized gain (loss) from futures contracts	$	76,363,644		$	—
	Net change in unrealized appreciation/depreciation on futures contracts		—			12,329,480