Statements of Changes in Capital - USD ($)
 3 Months Ended 12 Months Ended
Dec. 31, 2016
Mar. 31, 2016
Dec. 31, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Balances, Beginning   $ 524,750,880     $ 524,750,880    
Net income (loss)         (15,481,384) $ (104,689,203) $ (142,441,682)
Balances, Ending $ 643,918,233   $ 524,750,880   643,918,233 524,750,880  
United States Commodity Index Fund [Member]              
Balances, Beginning   520,635,970   $ 709,120,840 520,635,970 709,120,840 512,945,022
Additions         207,139,996 155,622,096 439,876,572
Redemptions         (75,843,491) (240,418,600) (101,862,281)
Net income (loss) (23,872,780) $ (2,080,163) (17,722,137) $ (47,696,670) (15,639,651) (103,688,366) (141,838,473)
Balances, Ending $ 636,292,824   $ 520,635,970   $ 636,292,824 $ 520,635,970 $ 709,120,840
Shares Outstanding, Beginning   12,850,000   14,700,000 12,850,000 14,700,000 9,150,000
Additions         4,900,000 3,500,000 7,500,000
Redemptions         (1,850,000) (5,350,000) (1,950,000)
Shares Outstanding, Ending 15,900,000   12,850,000   15,900,000 12,850,000 14,700,000
Net Asset Value Per Share:              
Net asset value, beginning of period (in dollars per share)   $ 40.52   $ 48.24 $ 40.52 $ 48.24 $ 56.06
Net asset value, end of period (in dollars per share) $ 40.02   $ 40.52   $ 40.02 $ 40.52 $ 48.24
United States Copper Index Fund [Member]              
Balances, Beginning   $ 2,135,390   $ 2,865,627 $ 2,135,390 $ 2,865,627 $ 2,292,199
Additions         3,352,232 799,533 3,118,249
Redemptions         0 (893,834) (2,139,551)
Net income (loss) $ 224,683 $ 10,749 $ (218,762) $ (118,292) 237,032 (635,936) (405,270)
Balances, Ending $ 5,724,654   $ 2,135,390   $ 5,724,654 $ 2,135,390 $ 2,865,627
Shares Outstanding, Beginning   150,000   150,000 150,000 150,000 100,000
Additions         200,000 50,000 150,000
Redemptions         0 (50,000) (100,000)
Shares Outstanding, Ending 350,000   150,000   350,000 150,000 150,000
Net Asset Value Per Share:              
Net asset value, beginning of period (in dollars per share)   $ 14.24   $ 19.10 $ 14.24 $ 19.10 $ 22.92
Net asset value, end of period (in dollars per share) $ 16.36   $ 14.24   $ 16.36 $ 14.24 $ 19.10
United States Agriculture Index Fund [Member]              
Balances, Beginning   $ 1,979,520   $ 2,296,602 $ 1,979,520 $ 2,296,602 $ 2,278,939
Additions         0 0 0
Redemptions         0 0 0
Net income (loss) $ (23,111) $ (14,968) $ (45,720) $ (208,832) (78,765) (317,082) 17,663
Balances, Ending $ 1,900,755   $ 1,979,520   $ 1,900,755 $ 1,979,520 $ 2,296,602
Shares Outstanding, Beginning   100,000   100,000 100,000 100,000 100,000
Additions         0 0 0
Redemptions         0 0 0
Shares Outstanding, Ending 100,000   100,000   100,000 100,000 100,000
Net Asset Value Per Share:              
Net asset value, beginning of period (in dollars per share)   $ 19.80   $ 22.97 $ 19.80 $ 22.97 $ 22.79
Net asset value, end of period (in dollars per share) $ 19.01   $ 19.80   $ 19.01 $ 19.80 $ 22.97
United States Commodity Index Funds Trust [Member]              
Balances, Beginning   $ 524,750,880   $ 716,264,689 $ 524,750,880 $ 716,264,689 $ 519,713,382
Additions         210,492,228 156,421,629 442,994,821
Redemptions         (75,843,491) (243,246,235) (104,001,832)
Net income (loss)         (15,481,384) (104,689,203) (142,441,682)
Balances, Ending $ 643,918,233   $ 524,750,880   $ 643,918,233 $ 524,750,880 $ 716,264,689
Shares Outstanding, Beginning   13,100,000   15,050,000 13,100,000 15,050,000 9,450,000
Additions         5,100,000 3,550,000 7,650,000
Redemptions         (1,850,000) (5,500,000) (2,050,000)
Shares Outstanding, Ending 16,350,000   13,100,000   16,350,000 13,100,000 15,050,000
Sponsor [Member] | United States Commodity Index Fund [Member]              
Balances, Beginning   $ 0   $ 0 $ 0 $ 0 $ 0
Additions         0 0 0
Redemptions         0 0 0
Net income (loss)         0 0 0
Balances, Ending $ 0   $ 0   $ 0 $ 0 $ 0
Shares Outstanding, Beginning   0   0 0 0 0
Additions         0 0 0
Redemptions         0 0 0
Shares Outstanding, Ending 0   0   0 0 0
Sponsor [Member] | United States Copper Index Fund [Member]              
Balances, Beginning   $ 0   $ 0 $ 0 $ 0 $ 0
Additions         0 0 0
Redemptions         0 0 0
Net income (loss)         0 0 0
Balances, Ending $ 0   $ 0   $ 0 $ 0 $ 0
Shares Outstanding, Beginning   0   0 0 0 0
Additions         0 0 0
Redemptions         0 0 0
Shares Outstanding, Ending 0   0   0 0 0
Sponsor [Member] | United States Agriculture Index Fund [Member]              
Balances, Beginning   $ 0   $ 0 $ 0 $ 0 $ 0
Additions         0 0 0
Redemptions         0 0 0
Net income (loss)         0 0 0
Balances, Ending $ 0   $ 0   $ 0 $ 0 $ 0
Shares Outstanding, Beginning   0   0 0 0 0
Additions         0 0 0
Redemptions         0 0 0
Shares Outstanding, Ending 0   0   0 0 0
Sponsor [Member] | United States Commodity Index Funds Trust [Member]              
Balances, Beginning   $ 0   $ 0 $ 0 $ 0 $ 0
Additions         0 0 0
Redemptions         0 0 0
Net income (loss)         0 0 0
Balances, Ending $ 0   $ 0   $ 0 $ 0 $ 0
Shares Outstanding, Beginning   0   0 0 0 0
Additions         0 0 0
Redemptions         0 0 0
Shares Outstanding, Ending 0   0   0 0 0
Shareholders [Member] | United States Commodity Index Fund [Member]              
Balances, Beginning   $ 520,635,970   $ 709,120,840 $ 520,635,970 $ 709,120,840 $ 512,945,022
Additions         207,139,996 155,622,096 439,876,572
Redemptions         (75,843,491) (240,418,600) (101,862,281)
Net income (loss)         (15,639,651) (103,688,366) (141,838,473)
Balances, Ending $ 636,292,824   $ 520,635,970   $ 636,292,824 $ 520,635,970 $ 709,120,840
Shares Outstanding, Beginning   12,850,000   14,700,000 12,850,000 14,700,000 9,150,000
Additions         4,900,000 3,500,000 7,500,000
Redemptions         (1,850,000) (5,350,000) (1,950,000)
Shares Outstanding, Ending 15,900,000   12,850,000   15,900,000 12,850,000 14,700,000
Shareholders [Member] | United States Copper Index Fund [Member]              
Balances, Beginning   $ 2,135,390   $ 2,865,627 $ 2,135,390 $ 2,865,627 $ 2,292,199
Additions         3,352,232 799,533 3,118,249
Redemptions         0 (893,834) (2,139,551)
Net income (loss)         237,032 (635,936) (405,270)
Balances, Ending $ 5,724,654   $ 2,135,390   $ 5,724,654 $ 2,135,390 $ 2,865,627
Shares Outstanding, Beginning   150,000   150,000 150,000 150,000 100,000
Additions         200,000 50,000 150,000
Redemptions         0 (50,000) (100,000)
Shares Outstanding, Ending 350,000   150,000   350,000 150,000 150,000
Shareholders [Member] | United States Agriculture Index Fund [Member]              
Balances, Beginning   $ 1,979,520   $ 2,296,602 $ 1,979,520 $ 2,296,602 $ 2,278,939
Additions         0 0 0
Redemptions         0 0 0
Net income (loss)         (78,765) (317,082) 17,663
Balances, Ending $ 1,900,755   $ 1,979,520   $ 1,900,755 $ 1,979,520 $ 2,296,602
Shares Outstanding, Beginning   100,000   100,000 100,000 100,000 100,000
Additions         0 0 0
Redemptions         0 0 0
Shares Outstanding, Ending 100,000   100,000   100,000 100,000 100,000
Shareholders [Member] | United States Commodity Index Funds Trust [Member]              
Balances, Beginning   $ 524,750,880   $ 716,264,689 $ 524,750,880 $ 716,264,689 $ 519,713,382
Additions         210,492,228 156,421,629 442,994,821
Redemptions         (75,843,491) (243,246,235) (104,001,832)
Net income (loss)         (15,481,384) (104,689,203) (142,441,682)
Balances, Ending $ 643,918,233   $ 524,750,880   $ 643,918,233 $ 524,750,880 $ 716,264,689
Shares Outstanding, Beginning   13,100,000   15,050,000 13,100,000 15,050,000 9,450,000
Additions         5,100,000 3,550,000 7,650,000
Redemptions         (1,850,000) (5,500,000) (2,050,000)
Shares Outstanding, Ending 16,350,000   13,100,000   16,350,000 13,100,000 15,050,000