FINANCIAL HIGHLIGHTS - Per Unit Performance Data and Other Supplemental Financial Data (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
United States Commodity Index Fund
Per Share Operating Performance:
Net asset value, beginning of period (in dollars per share)	$ 37.49	$ 42.48	$ 40.02
Total income (loss)	(0.21)	(4.56)	2.87
Total expenses	(0.41)	(0.43)	(0.41)
Net increase (decrease) in net asset value	(0.62)	(4.99)	2.46
Net asset value, end of period (in dollars per share)	$ 36.87	$ 37.49	$ 42.48
Total Return	(1.65%)	(11.75%)	6.15%
Ratios to Average Net Assets
Total income (loss)	(1.32%)	(11.33%)	6.17%
Management fees	0.80%	0.80%	0.80%
Total expenses excluding management fees	0.30%	0.23%	0.24%
Net expenses excluding management fees	0.30%	0.23%	0.24%
Net income (loss)	(2.42%)	(12.36%)	5.14%
United States Copper Index Fund
Per Share Operating Performance:
Net asset value, beginning of period (in dollars per share)	$ 16.44	$ 21.05	$ 16.36
Total income (loss)	1.24	(4.46)	4.83
Total expenses	(0.14)	(0.15)	(0.14)
Net increase (decrease) in net asset value	1.10	(4.61)	4.69
Net asset value, end of period (in dollars per share)	$ 17.54	$ 16.44	$ 21.05
Total Return	6.69%	(21.90%)	28.67%
Ratios to Average Net Assets
Total income (loss)	3.36%	(24.49%)	22.70%
Management fees	0.65%	0.65%	0.65%
Total expenses excluding management fees	0.79%	0.58%	0.54%
Expenses waived	(0.64%)	(0.43%)	(0.39%)
Net expenses excluding management fees	0.15%	0.15%	0.15%
Net income (loss)	2.56%	(25.29%)	21.90%