CONTRACTS AND AGREEMENTS (Brokerage Commissions) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Total commissions accrued to brokers	$ 2,209	$ 3,451	$ 6,117
Total commissions as annualized percentage of average total net assets	0.02%	0.03%	0.04%
Rebalancing Investments Transaction [Member]
Total commissions accrued to brokers	$ 1,605	$ 3,305	$ 4,698
Total commissions as annualized percentage of average total net assets	72.66%	95.77%	76.80%
Creation And Redemption Activity [Member]
Total commissions accrued to brokers	$ 604	$ 146	$ 1,419
Total commissions as annualized percentage of average total net assets	27.34%	4.23%	23.20%