FAIR VALUE OF FINANCIAL INSTRUMENTS - Valuation of Securities Using Fair Value Hierarchy (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
United States Commodity Index Fund
FAIR VALUE OF FINANCIAL INSTRUMENTS
Transfers between Level I to Level II	$ 0	$ 0
Transfers between Level II to Level I	0	0
United States Commodity Index Fund \| Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	188,989,355	436,426,995
United States Commodity Index Fund \| Exchange-Traded Futures Contracts \| Foreign Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	(2,381,779)	(1,866,820)
United States Commodity Index Fund \| Exchange-Traded Futures Contracts \| United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	4,520,647	(12,621,164)
United States Commodity Index Fund \| Level I \| Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	188,989,355	436,426,995
United States Commodity Index Fund \| Level I \| Exchange-Traded Futures Contracts \| Foreign Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	(2,381,779)	(1,866,820)
United States Commodity Index Fund \| Level I \| Exchange-Traded Futures Contracts \| United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	4,520,647	(12,621,164)
United States Commodity Index Fund \| Level II \| Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	0	0
United States Commodity Index Fund \| Level II \| Exchange-Traded Futures Contracts \| Foreign Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	0	0
United States Commodity Index Fund \| Level II \| Exchange-Traded Futures Contracts \| United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	0	0
United States Commodity Index Fund \| Level III \| Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	0	0
United States Commodity Index Fund \| Level III \| Exchange-Traded Futures Contracts \| Foreign Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	0	0
United States Commodity Index Fund \| Level III \| Exchange-Traded Futures Contracts \| United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	0	0
United States Copper Index Fund
FAIR VALUE OF FINANCIAL INSTRUMENTS
Transfers between Level I to Level II	0	0
Transfers between Level II to Level I	0	0
United States Copper Index Fund \| Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	7,096,018	9,657,426
United States Copper Index Fund \| Exchange-Traded Futures Contracts \| United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	346,250	(903,475)
United States Copper Index Fund \| Level I \| Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	7,096,018	9,657,426
United States Copper Index Fund \| Level I \| Exchange-Traded Futures Contracts \| United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	346,250	(903,475)
United States Copper Index Fund \| Level II \| Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	0	0
United States Copper Index Fund \| Level II \| Exchange-Traded Futures Contracts \| United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	0	0
United States Copper Index Fund \| Level III \| Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	0	0
United States Copper Index Fund \| Level III \| Exchange-Traded Futures Contracts \| United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	$ 0	$ 0

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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