Statements of Cash Flows - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Cash Flows from Operating Activities:      
Net income (loss) $ (15,481,384) $ (104,689,203) $ (142,441,682)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:      
(Increase) decrease in commodity futures trading account - cash and cash equivalents 16,052,639 24,535,826 (60,098,264)
Unrealized (gain) loss on open futures contracts (10,811,030) (29,911,129) 49,496,908
(Increase) decrease in receivable from Sponsor (31,888) 3,829 125,972
(Increase) decrease in interest receivable 46 36 0
(Increase) decrease in directors' fees and insurance receivable 6,222 (6,222) 0
(Increase) decrease in ETF transaction fees receivable (350) 1,050 (700)
Increase (decrease) in management fees payable 87,459 (172,944) 128,225
Increase (decrease) in professional fees payable (75,269) 163,900 18,255
Increase (decrease) in brokerage commissions payable 11,200 0 20,000
Increase (decrease) in directors' fees and insurance payable 6,162 (15,792) 7,553
Increase (decrease) in registration fees payable 0 0 (152)
Net cash provided by (used in) operating activities (10,236,193) (110,090,649) (152,743,885)
Cash Flows from Financing Activities:      
Addition of shares 210,492,228 156,421,629 451,486,732
Redemption of shares (69,828,108) (286,982,884) (60,265,183)
Net cash provided by (used in) financing activities 140,664,120 (130,561,255) 391,221,549
Net Increase (Decrease) in Cash and Cash Equivalents 130,427,927 (240,651,904) 238,477,664
Cash and Cash Equivalents, beginning of year 478,007,269 718,659,173 480,181,509
Cash and Cash Equivalents, end of year 608,435,196 478,007,269 718,659,173
United States Commodity Index Fund [Member]      
Cash Flows from Operating Activities:      
Net income (loss) (15,639,651) (103,688,366) (141,838,473)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:      
(Increase) decrease in commodity futures trading account - cash and cash equivalents 15,941,203 24,230,603 (59,905,773)
Unrealized (gain) loss on open futures contracts (10,637,687) (29,684,932) 49,056,906
(Increase) decrease in directors' fees and insurance receivable 6,190 (6,190) 0
(Increase) decrease in ETF transaction fees receivable (350) 1,050 (700)
Increase (decrease) in management fees payable 85,619 (172,237) 128,287
Increase (decrease) in professional fees payable (133,821) 199,184 151,042
Increase (decrease) in brokerage commissions payable 11,200 0 20,000
Increase (decrease) in directors' fees and insurance payable 6,164 (15,638) 7,439
Increase (decrease) in registration fees payable 0 0 (152)
Net cash provided by (used in) operating activities (10,361,133) (109,136,526) (152,381,424)
Cash Flows from Financing Activities:      
Addition of shares 207,139,996 155,622,096 448,368,483
Redemption of shares (69,828,108) (284,155,249) (58,125,632)
Net cash provided by (used in) financing activities 137,311,888 (128,533,153) 390,242,851
Net Increase (Decrease) in Cash and Cash Equivalents 126,950,755 (237,669,679) 237,861,427
Cash and Cash Equivalents, beginning of year 474,315,271 711,984,950 474,123,523
Cash and Cash Equivalents, end of year 601,266,026 474,315,271 711,984,950
United States Copper Index Fund [Member]      
Cash Flows from Operating Activities:      
Net income (loss) 237,032 (635,936) (405,270)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:      
(Increase) decrease in commodity futures trading account - cash and cash equivalents 180,275 (96,292) (211,188)
Unrealized (gain) loss on open futures contracts (269,200) (16,900) 327,688
(Increase) decrease in receivable from Sponsor (16,039) (16,771) 38,959
(Increase) decrease in interest receivable 0 25 0
(Increase) decrease in directors' fees and insurance receivable 32 (32) 0
Increase (decrease) in management fees payable 1,882 (456) 383
Increase (decrease) in professional fees payable 30,138 2,581 (40,651)
Increase (decrease) in directors' fees and insurance payable 47 (35) 19
Net cash provided by (used in) operating activities 164,167 (763,816) (290,060)
Cash Flows from Financing Activities:      
Addition of shares 3,352,232 799,533 3,118,249
Redemption of shares 0 (893,834) (2,139,551)
Net cash provided by (used in) financing activities 3,352,232 (94,301) 978,698
Net Increase (Decrease) in Cash and Cash Equivalents 3,516,399 (858,117) 688,638
Cash and Cash Equivalents, beginning of year 1,871,256 2,729,373 2,040,735
Cash and Cash Equivalents, end of year 5,387,655 1,871,256 2,729,373
United States Agricultural Index Fund [Member]      
Cash Flows from Operating Activities:      
Net income (loss) (78,765) (317,082) 17,663
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:      
(Increase) decrease in commodity futures trading account - cash and cash equivalents (68,839) 83,359 7,255
Unrealized (gain) loss on open futures contracts 95,857 (72,733) 22,043
(Increase) decrease in receivable from Sponsor (15,849) (17,185) 42,633
(Increase) decrease in interest receivable 46 0 0
Increase (decrease) in management fees payable (42) 877 (276)
Increase (decrease) in professional fees payable 28,414 1,131 (45,500)
Increase (decrease) in directors' fees and insurance payable (49) (40) 52
Net cash provided by (used in) operating activities (39,227) (321,673) 43,870
Cash Flows from Financing Activities:      
Addition of shares 0 0 0
Redemption of shares 0 0 0
Net cash provided by (used in) financing activities 0 0 0
Net Increase (Decrease) in Cash and Cash Equivalents (39,227) (321,673) 43,870
Cash and Cash Equivalents, beginning of year 1,820,742 2,142,415 2,098,545
Cash and Cash Equivalents, end of year $ 1,781,515 $ 1,820,742 $ 2,142,415