Statement of Changes in Shareholders' Equity (Unaudited) - USD ($)	Total	General Shares [Member]	Shares [Member]
Balance - Value at Dec. 31, 2016	$ 284,135,889	$ 598	$ 284,135,291
Balance - Shares at Dec. 31, 2016		40	19,000,000
Purchases of Shares - Value	75,468,713		$ 75,468,713
Purchases of Shares - Shares			4,600,000
Redemption of Shares - Value	(120,985,255)		$ (120,985,255)
Redemption of Shares - Shares			(7,600,000)
Net Increase (Decrease) due to Share Transactions, value	(45,516,542)		$ (45,516,542)
Net Increase (Decrease) due to Share Transactions, shares			(3,000,000)
Net Income (Loss)
Net Investment Income (Loss)	(291,493)	$ (1)	$ (291,492)
Net Realized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Commodity Futures Contracts	34,000,193	84	34,000,109
Net Change in Unrealized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Commodity Futures Contracts	16,966,431	42	16,966,389
Net Income (Loss)	50,675,131	125	50,675,006
Net Change in Shareholders' Equity, value	5,158,589	125	$ 5,158,464
Net Change in Shareholders' Equity, shares			(3,000,000)
Balance - Value at Sep. 30, 2017	289,294,478	$ 723	$ 289,293,755
Balance - Shares at Sep. 30, 2017		40	16,000,000
Balance - Value at Jun. 30, 2017	208,773,760	$ 652	$ 208,773,108
Balance - Shares at Jun. 30, 2017		40	12,800,000
Purchases of Shares - Value	59,805,302		$ 59,805,302
Purchases of Shares - Shares			3,600,000
Redemption of Shares - Value	(7,365,097)		$ (7,365,097)
Redemption of Shares - Shares			(400,000)
Net Increase (Decrease) due to Share Transactions, value	52,440,205		$ 52,440,205
Net Increase (Decrease) due to Share Transactions, shares			3,200,000
Net Income (Loss)
Net Investment Income (Loss)	18,164		$ 18,164
Net Realized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Commodity Futures Contracts	15,257,328	$ 39	15,257,289
Net Change in Unrealized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Commodity Futures Contracts	12,805,021	32	12,804,989
Net Income (Loss)	28,080,513	71	28,080,442
Net Change in Shareholders' Equity, value	80,520,718	71	$ 80,520,647
Net Change in Shareholders' Equity, shares			3,200,000
Balance - Value at Sep. 30, 2017	289,294,478	$ 723	$ 289,293,755
Balance - Shares at Sep. 30, 2017		40	16,000,000
Balance - Value at Dec. 31, 2017	314,091,261	$ 776	$ 314,090,485
Balance - Shares at Dec. 31, 2017		40	16,200,000
Purchases of Shares - Value	94,060,843		$ 94,060,843
Purchases of Shares - Shares			5,000,000
Redemption of Shares - Value	(167,590,708)		$ (167,590,708)
Redemption of Shares - Shares			(9,800,000)
Net Increase (Decrease) due to Share Transactions, value	(73,529,865)		$ (73,529,865)
Net Increase (Decrease) due to Share Transactions, shares			(4,800,000)
Net Income (Loss)
Net Investment Income (Loss)	2,030,200	$ 4	$ 2,030,196
Net Realized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Commodity Futures Contracts	(1,380,065)	(3)	(1,380,062)
Net Change in Unrealized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Commodity Futures Contracts	(51,256,109)	(111)	(51,255,998)
Net Income (Loss)	(50,605,974)	(110)	(50,605,864)
Net Change in Shareholders' Equity, value	(124,135,839)	(110)	$ (124,135,729)
Net Change in Shareholders' Equity, shares			(4,800,000)
Balance - Value at Sep. 30, 2018	189,955,422	$ 666	$ 189,954,756
Balance - Shares at Sep. 30, 2018		40	11,400,000
Balance - Value at Jun. 30, 2018	306,717,641	$ 705	$ 306,716,936
Balance - Shares at Jun. 30, 2018		40	17,400,000
Purchases of Shares - Value	9,734,482		$ 9,734,482
Purchases of Shares - Shares			600,000
Redemption of Shares - Value	(108,008,540)		$ (108,008,540)
Redemption of Shares - Shares			(6,600,000)
Net Increase (Decrease) due to Share Transactions, value	(98,274,058)		$ (98,274,058)
Net Increase (Decrease) due to Share Transactions, shares			(6,000,000)
Net Income (Loss)
Net Investment Income (Loss)	859,617	$ 2	$ 859,615
Net Realized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Commodity Futures Contracts	(19,386,197)	(43)	(19,386,154)
Net Change in Unrealized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Commodity Futures Contracts	38,419	2	38,417
Net Income (Loss)	(18,488,161)	(39)	(18,488,122)
Net Change in Shareholders' Equity, value	(116,762,219)	(39)	$ (116,762,180)
Net Change in Shareholders' Equity, shares			(6,000,000)
Balance - Value at Sep. 30, 2018	$ 189,955,422	$ 666	$ 189,954,756
Balance - Shares at Sep. 30, 2018		40	11,400,000