Condensed Statements of Cash Flows (Parenthetical) - USD ($)	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
United States Commodity Index Fund [Member]
Components of Cash and Cash Equivalents:
Cash and Cash Equivalents	$ 403,949,418	$ 427,657,030	$ 488,134,267
Equity in Trading Accounts:
Cash and Cash Equivalents	35,952,692		31,784,112
Total Cash, Cash Equivalents and Equity in Trading Accounts	439,902,110		519,918,379
United States Copper Index Fund [Member]
Components of Cash and Cash Equivalents:
Cash and Cash Equivalents	15,373,384	10,753,786	10,662,859
Equity in Trading Accounts:
Cash and Cash Equivalents	599,223		1,740,516
Total Cash, Cash Equivalents and Equity in Trading Accounts	15,972,607		12,403,375
United States Commodity Index Funds Trust [Member]
Components of Cash and Cash Equivalents:
Cash and Cash Equivalents	419,322,802	$ 438,410,816	500,187,061
Equity in Trading Accounts:
Cash and Cash Equivalents	36,551,915		33,634,753
Total Cash, Cash Equivalents and Equity in Trading Accounts	$ 455,874,717		$ 533,821,814