FAIR VALUE OF FINANCIAL INSTRUMENTS - Valuation of Securities Using Fair Value Hierarchy (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
United States Commodity Index Fund | Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	$ 218,101,877	$ 103,316,877
United States Commodity Index Fund | Exchange-Traded Futures Contracts | Foreign Contracts.
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	(1,624,494)	240,280
United States Commodity Index Fund | Exchange-Traded Futures Contracts | United States Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	7,590,906	7,053,064
United States Commodity Index Fund | Level I | Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	218,101,877	103,316,877
United States Commodity Index Fund | Level I | Exchange-Traded Futures Contracts | Foreign Contracts.
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	(1,624,494)	240,280
United States Commodity Index Fund | Level I | Exchange-Traded Futures Contracts | United States Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	7,590,906	7,053,064
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 Contracts
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 Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	0	0
United States Copper Index Fund | Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	248,955,787	62,332,787
United States Copper Index Fund | Exchange-Traded Futures Contracts | United States Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	(3,576,834)	4,296,063
United States Copper Index Fund | Level I | Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	248,955,787	62,332,787
United States Copper Index Fund | Level I | Exchange-Traded Futures Contracts | United States Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	(3,576,834)	4,296,063
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 Contracts
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 Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	$ 0	$ 0