STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from (for) operating activities
Net income (loss)	$ (28,728,209)	$ (2,309,667)	$ (72,322,270)
Adjustments to reconcile net income (loss) to net cash from (for) operating activities
Net change in unrealized on futures, forwards and investments	(2,068,918)	(888,535)	(11,938,722)
(Increase) decrease in interest receivable	121,306	23,875	144,366
Increase (decrease) in accounts payable and accrued expenses	(527,011)	(767,786)	(1,051,941)
Purchases of investments	(2,712,465,922)	(3,485,481,332)	(5,323,635,527)
Sales/maturities of investments	2,802,502,188	3,607,934,569	5,457,978,355
Net cash from (for) operating activities	58,833,434	118,511,124	49,174,261
Cash flows from (for) financing activities
Redemption of units	(55,612,737)	(115,178,379)	(81,421,815)
Offering costs paid	(848,573)	(953,077)	(1,327,186)
Net cash from (for) financing activities	(56,461,310)	(116,131,456)	(82,749,001)
Net increase (decrease) in cash, cash equivalents and restricted cash	2,372,124	2,379,668	(33,574,740)
Cash, cash equivalents and restricted cash at beginning of year	25,795,630	23,415,962	56,990,702
Total cash, cash equivalents and restricted cash at end of year	$ 28,167,754	$ 25,795,630	$ 23,415,962