FAIR VALUE OF FINANCIAL INSTRUMENTS - Valuation of Securities Using Fair Value Hierarchy (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
United States Commodity Index Fund | Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	$ 98,490,861	$ 188,989,355
United States Commodity Index Fund | Exchange-Traded Futures Contracts | Foreign Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	1,356,885	(2,381,779)
United States Commodity Index Fund | Exchange-Traded Futures Contracts | United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	4,124,734	4,520,647
United States Commodity Index Fund | Level I | Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	98,490,861	188,989,355
United States Commodity Index Fund | Level I | Exchange-Traded Futures Contracts | Foreign Contracts
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	1,356,885	(2,381,779)
United States Commodity Index Fund | Level I | Exchange-Traded Futures Contracts | United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	4,124,734	4,520,647
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 | Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	26,217,685	7,096,018
United States Copper Index Fund | Exchange-Traded Futures Contracts | United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	1,610,888	346,250
United States Copper Index Fund | Level I | Short-Term Investments
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	26,217,685	7,096,018
United States Copper Index Fund | Level I | Exchange-Traded Futures Contracts | United States
FAIR VALUE OF FINANCIAL INSTRUMENTS
Securities, fair value	1,610,888	346,250
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