Condensed Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
United States Commodity Index Fund [Member]
Cash Flows from Operating Activities:
Net income (loss)	$ 16,243,487	$ 2,873,099
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
(Increase) decrease in short-term investments	0	35,669,917
Unrealized (gain) loss on open futures contracts	(18,150,103)	2,082,239
(Increase) decrease in dividends receivable	(40,522)	0
(Increase) decrease in interest receivable	3,734	(34,098)
(Increase) decrease in directors' fees and insurance receivable	6,567	0
(Increase) decrease in ETF transaction fees receivable	0	350
Increase (decrease) in payable due to Broker	4,319,226	0
Increase (decrease) in management fees payable	(64,671)	12,052
Increase (decrease) in professional fees payable	(210,925)	(128,912)
Increase (decrease) in directors' fees and insurance payable	0	7,381
Net cash provided by (used in) operating activities	2,106,793	40,482,028
Cash Flows from Financing Activities:
Addition of shares	0	57,599,905
Redemption of shares	(40,713,896)	(4,261,429)
Net cash provided by (used in) financing activities	(40,713,896)	53,338,476
Net Increase (Decrease) in Cash and Cash Equivalents	(38,607,103)	93,820,504
Total Cash, Cash Equivalents and Equity in Trading Accounts, beginning of period	478,509,213	426,097,875
Total Cash, Cash Equivalents and Equity in Trading Accounts, end of period	439,902,110	519,918,379
United States Copper Index Fund [Member]
Cash Flows from Operating Activities:
Net income (loss)	1,219,154	(1,206,325)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
(Increase) decrease in short-term investments	295,216	395,657
Unrealized (gain) loss on open futures contracts	(1,436,100)	1,589,363
(Increase) decrease in receivable from Sponsor	(21,919)	(8,269)
(Increase) decrease in dividends receivable	(2,286)	0
(Increase) decrease in interest receivable	160	(2,563)
(Increase) decrease in directors' fees and insurance receivable	0	35
Increase (decrease) in payable due to Broker	14,739	(442,429)
Increase (decrease) in management fees payable	428	1,477
Increase (decrease) in professional fees payable	(13,175)	(20,569)
Increase (decrease) in directors' fees and insurance payable	236	337
Net cash provided by (used in) operating activities	56,453	306,714
Cash Flows from Financing Activities:
Addition of shares	5,451,099	4,174,486
Redemption of shares	(1,651,189)	0
Net cash provided by (used in) financing activities	3,799,910	4,174,486
Net Increase (Decrease) in Cash and Cash Equivalents	3,856,363	4,481,200
Total Cash, Cash Equivalents and Equity in Trading Accounts, beginning of period	12,116,244	7,922,175
Total Cash, Cash Equivalents and Equity in Trading Accounts, end of period	15,972,607	12,403,375
United States Commodity Index Funds Trust [Member]
Cash Flows from Operating Activities:
Net income (loss)	17,462,641	1,649,964
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
(Increase) decrease in short-term investments	295,216	36,164,341
Unrealized (gain) loss on open futures contracts	(19,586,203)	3,660,316
(Increase) decrease in receivable from Sponsor	(21,919)	(19,168)
(Increase) decrease in dividends receivable	(42,808)	0
(Increase) decrease in interest receivable	3,894	(36,907)
(Increase) decrease in directors' fees and insurance receivable	6,567	218
(Increase) decrease in ETF transaction fees receivable	0	350
Increase (decrease) in payable due to Broker	4,333,965	(442,429)
Increase (decrease) in management fees payable	(64,243)	12,235
Increase (decrease) in professional fees payable	(224,100)	(165,362)
Increase (decrease) in directors' fees and insurance payable	236	7,762
Net cash provided by (used in) operating activities	2,163,246	40,831,320
Cash Flows from Financing Activities:
Addition of shares	5,451,099	61,775,391
Redemption of shares	(42,365,085)	(4,261,429)
Net cash provided by (used in) financing activities	(36,913,986)	57,513,962
Net Increase (Decrease) in Cash and Cash Equivalents	(34,750,740)	98,345,282
Total Cash, Cash Equivalents and Equity in Trading Accounts, beginning of period	490,625,457	435,476,532
Total Cash, Cash Equivalents and Equity in Trading Accounts, end of period	$ 455,874,717	$ 533,821,814