Condensed Statements of Financial Condition - USD ($)	Mar. 31, 2019	Dec. 31, 2018
United States Commodity Index Fund [Member]
Assets
Cash and cash equivalents	$ 403,949,418	$ 427,657,030
Equity in trading accounts:
Cash and cash equivalents	35,952,692	50,852,183
Unrealized gain (loss) on open commodity futures contracts	3,662,119	(14,487,984)
Dividends receivable	50,505	9,983
Interest receivable	490	4,224
Directors' fees and insurance receivable	15,752	22,319
Total assets	443,630,976	464,057,755
Liabilities and Capital
Payable due to Broker	4,319,226	0
Management fees payable (Note 4)	302,975	367,646
Professional fees payable	393,371	604,296
Brokerage commissions payable	43,305	43,305
Total liabilities	5,058,877	1,015,247
Commitments and Contingencies (Notes 4, 5 and 6)
Capital
Sponsor	0	0
Shareholders	438,572,099	463,042,508
Total Capital	438,572,099	463,042,508
Total liabilities and capital	$ 443,630,976	$ 464,057,755
Shares outstanding	11,300,000	12,350,000
Net asset value per share	$ 38.81	$ 37.49
Market value per share	$ 38.73	$ 37.53
United States Copper Index Fund [Member]
Assets
Cash and cash equivalents	$ 15,373,384	$ 10,753,786
Short-Term Investments	0	295,216
Equity in trading accounts:
Cash and cash equivalents	599,223	1,362,458
Unrealized gain (loss) on open commodity futures contracts	532,625	(903,475)
Receivable from Sponsor (Note 4)	73,218	51,299
Dividends receivable	3,642	1,356
Interest receivable	61	221
Total assets	16,582,153	11,560,861
Liabilities and Capital
Payable due to Broker	14,739	0
Management fees payable (Note 4)	6,541	6,113
Professional fees payable	36,625	49,800
Directors' fees and insurance payable	289	53
Total liabilities	58,194	55,966
Commitments and Contingencies (Notes 4, 5 and 6)
Capital
Sponsor	0	0
Shareholders	16,523,959	11,504,895
Total Capital	16,523,959	11,504,895
Total liabilities and capital	$ 16,582,153	$ 11,560,861
Shares outstanding	900,000	700,000
Net asset value per share	$ 18.36	$ 16.44
Market value per share	$ 18.32	$ 16.44
United States Commodity Index Funds Trust [Member]
Assets
Cash and cash equivalents	$ 419,322,802	$ 438,410,816
Short-Term Investments	0	295,216
Equity in trading accounts:
Cash and cash equivalents	36,551,915	52,214,641
Unrealized gain (loss) on open commodity futures contracts	4,194,744	(15,391,459)
Receivable from Sponsor (Note 4)	73,218	51,299
Dividends receivable	54,147	11,339
Interest receivable	551	4,445
Directors' fees and insurance receivable	15,752	22,319
Total assets	460,213,129	475,618,616
Liabilities and Capital
Payable due to Broker	4,333,965	0
Management fees payable (Note 4)	309,516	373,759
Professional fees payable	429,996	654,096
Brokerage commissions payable	43,305	43,305
Directors' fees and insurance payable	289	53
Total liabilities	5,117,071	1,071,213
Commitments and Contingencies (Notes 4, 5 and 6)
Capital
Sponsor	0	0
Shareholders	455,096,058	474,547,403
Total Capital	455,096,058	474,547,403
Total liabilities and capital	$ 460,213,129	$ 475,618,616
Shares outstanding	12,200,000	13,050,000