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CONTRACTS AND AGREEMENTS (Brokerage Commissions) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total commissions accrued to brokers	$ 1,334	$ 2,209	$ 3,451
Total commissions as annualized percentage of average total net assets	0.02%	0.02%	0.03%
Rebalancing Investments Transaction [Member]
Total commissions accrued to brokers	$ 823	$ 1,605	$ 3,305
Total commissions as annualized percentage of average total net assets	61.69%	72.66%	95.77%
Creation And Redemption Activity [Member]
Total commissions accrued to brokers	$ 511	$ 604	$ 146
Total commissions as annualized percentage of average total net assets	38.31%	27.34%	4.23%