Schedule of Investments (Unaudited) - Treasury Bills (Parenthetical) - USD ($)		6 Months Ended	12 Months Ended
		Jun. 30, 2015	Dec. 31, 2014
U.S. Treasury Bills, 0.005% due July 2, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]	0.005%
Investment maturity date	[1],[2]	Jul. 02, 2015
U.S. Treasury Bills, 0.000% due July 23, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]	0.00%
Investment maturity date	[1],[2]	Jul. 23, 2015
U.S. Treasury Bills, 0.015% due July 30, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]	0.015%
Investment maturity date	[1],[2]	Jul. 30, 2015
U.S. Treasury Bills, 0.015% due August 6, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]	0.015%
Investment maturity date	[1],[2]	Aug. 06, 2015
U.S. Treasury Bills, 0.020% due August 13, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]	0.02%
Investment maturity date	[1],[2]	Aug. 13, 2015
U.S. Treasury Bills, 0.015% due August 20, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]	0.015%
Investment maturity date	[1],[2]	Aug. 20, 2015
U.S. Treasury Bills, 0.015% due September 10, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]	0.015%
Investment maturity date	[1],[2]	Sep. 10, 2015
Total United States Treasury Obligations [Member]
Schedule of Investments [Line Items]
Total United States Treasury Obligations, cost		$ 216,996,933	$ 236,993,093
U.S. Treasury Bills, 0.030% due January 2, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]		0.03%
Investment maturity date	[1],[2]		Jan. 02, 2015
U.S. Treasury Bills, 0.020% due January 15, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]		0.02%
Investment maturity date	[1],[2]		Jan. 15, 2015
U.S. Treasury Bills, 0.010% due January 22, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]		0.01%
Investment maturity date	[1],[2]		Jan. 22, 2015
U.S. Treasury Bills, 0.015% due January 29, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]		0.015%
Investment maturity date	[1],[2]		Jan. 29, 2015
U.S. Treasury Bills, 0.010% due February 5, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]		0.01%
Investment maturity date	[1],[2]		Feb. 05, 2015
U.S. Treasury Bills, 0.025% due February 12, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]		0.025%
Investment maturity date	[1],[2]		Feb. 12, 2015
U.S. Treasury Bills, 0.025% due March 12, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]		0.025%
Investment maturity date	[1],[2]		Mar. 12, 2015
U.S. Treasury Bills, 0.055% due March 26, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]		0.055%
Investment maturity date	[1],[2]		Mar. 26, 2015
U.S. Treasury Bills, 0.040% due April 2, 2015 [Member]
Schedule of Investments [Line Items]
Investment interest rate	[1],[2]		0.04%
Investment maturity date	[1],[2]		Apr. 02, 2015

[1] A portion of United States Treasury Obligations are on deposit with the commodity broker and held as margin for open futures contracts. See Note 3 for additional information.

[2] Security may be traded on a discount basis. The interest rate shown represents the discount rate at the most recent auction date of the security prior to period end.