Condensed Statements of Operations - USD ($)		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
United States Commodity Index Fund [Member]
Gain (loss) on trading of commodity futures contracts:
Realized gain (loss) on closed positions		$ (3,351,005)	$ 4,628,257
Change in unrealized gain (loss) on open positions		18,150,103	(2,082,239)
Dividend income		114,031	0
Interest income	[1]	2,602,041	1,712,166
ETF transaction fees		4,200	5,950
Total income (loss)		17,519,370	4,264,134
Expenses
Management fees (Note 4)		912,419	1,038,924
Professional fees		164,254	164,254
Brokerage commissions		176,921	169,522
Directors' fees and insurance		22,289	18,335
Total expenses		1,275,883	1,391,035
Net income (loss)		$ 16,243,487	$ 2,873,099
Net income (loss) per share (in dollars per share)		$ 1.32	$ 0.24
Net income (loss) per weighted average share (in dollars per share)		$ 1.36	$ 0.23
Weighted average shares outstanding (in shares)		11,936,667	12,357,222
United States Copper Index Fund [Member]
Gain (loss) on trading of commodity futures contracts:
Realized gain (loss) on closed positions		$ (263,113)	$ 362,412
Change in unrealized gain (loss) on open positions		1,436,100	(1,589,363)
Dividend income		7,079	0
Interest income	[1]	59,658	47,066
ETF transaction fees		2,450	1,050
Total income (loss)		1,242,174	(1,178,835)
Expenses
Management fees (Note 4)		18,704	22,329
Professional fees		24,164	10,664
Brokerage commissions		1,509	2,198
Directors' fees and insurance		561	568
Total expenses		44,938	35,759
Expense waiver (Note 4)		(21,918)	(8,269)
Net expenses		23,020	27,490
Net income (loss)		$ 1,219,154	$ (1,206,325)
Net income (loss) per share (in dollars per share)		$ 1.92	$ (1.75)
Net income (loss) per weighted average share (in dollars per share)		$ 1.83	$ (1.75)
Weighted average shares outstanding (in shares)		665,556	691,111
United States Commodity Index Funds Trust [Member]
Gain (loss) on trading of commodity futures contracts:
Realized gain (loss) on closed positions		$ (3,614,118)	$ 4,960,130
Change in unrealized gain (loss) on open positions		19,586,203	(3,660,316)
Realized gain (loss) on foreign currency transactions		0	47
Change in unrealized gain (loss) on foreign currency translations		0	(15)
Dividend income		121,110	0
Interest income	[1]	2,661,699	1,765,173
ETF transaction fees		6,650	7,000
Total income (loss)		18,761,544	3,072,019
Expenses
Management fees (Note 4)		931,123	1,064,078
Professional fees		188,418	185,582
Brokerage commissions		178,430	172,393
Directors' fees and insurance		22,850	19,170
Total expenses		1,320,821	1,441,223
Expense waiver (Note 4)		(21,918)	(19,168)
Net expenses		1,298,903	1,422,055
Net income (loss)		$ 17,462,641	$ 1,649,964

[1] Interest income does not exceed paid in kind of 5%.