Schedule of Investments (Unaudited) - Treasury Bills - USD ($)		Jun. 30, 2015	Dec. 31, 2014
Schedule of Investments [Line Items]
Fair Value		$ 217,001,291	$ 236,994,724
U.S. Treasury Bills, 0.005% due July 2, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	4.27%
Fair Value	[1],[2]	$ 8,000,000
Face Value	[1],[2]	$ 8,000,000
U.S. Treasury Bills, 0.000% due July 23, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	6.41%
Fair Value	[1],[2]	$ 12,000,024
Face Value	[1],[2]	$ 12,000,000
U.S. Treasury Bills, 0.015% due July 30, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	13.35%
Fair Value	[1],[2]	$ 24,999,700
Face Value	[1],[2]	$ 25,000,000
U.S. Treasury Bills, 0.015% due August 6, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	26.70%
Fair Value	[1],[2]	$ 50,000,250
Face Value	[1],[2]	$ 50,000,000
U.S. Treasury Bills, 0.020% due August 13, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	30.43%
Fair Value	[1],[2]	$ 57,000,342
Face Value	[1],[2]	$ 57,000,000
U.S. Treasury Bills, 0.015% due August 20, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	21.36%
Fair Value	[1],[2]	$ 40,000,000
Face Value	[1],[2]	$ 40,000,000
U.S. Treasury Bills, 0.015% due September 10, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	13.35%
Fair Value	[1],[2]	$ 25,000,975
Face Value	[1],[2]	$ 25,000,000
Total United States Treasury Obligations [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	115.87%	107.41%
Fair Value	[1],[2]	$ 217,001,291	$ 236,994,724
U.S. Treasury Bills, 0.030% due January 2, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]		10.42%
Fair Value	[1],[2]		$ 23,000,000
Face Value	[1],[2]		$ 23,000,000
U.S. Treasury Bills, 0.020% due January 15, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]		3.63%
Fair Value	[1],[2]		$ 7,999,944
Face Value	[1],[2]		$ 8,000,000
U.S. Treasury Bills, 0.010% due January 22, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]		18.13%
Fair Value	[1],[2]		$ 39,999,440
Face Value	[1],[2]		$ 40,000,000
U.S. Treasury Bills, 0.015% due January 29, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]		21.30%
Fair Value	[1],[2]		$ 46,999,295
Face Value	[1],[2]		$ 47,000,000
U.S. Treasury Bills, 0.010% due February 5, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]		23.57%
Fair Value	[1],[2]		$ 51,999,012
Face Value	[1],[2]		$ 52,000,000
U.S. Treasury Bills, 0.025% due February 12, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]		10.88%
Fair Value	[1],[2]		$ 23,999,664
Face Value	[1],[2]		$ 24,000,000
U.S. Treasury Bills, 0.025% due March 12, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]		1.36%
Fair Value	[1],[2]		$ 2,999,886
Face Value	[1],[2]		$ 3,000,000
U.S. Treasury Bills, 0.055% due March 26, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]		7.70%
Fair Value	[1],[2]		$ 16,999,507
Face Value	[1],[2]		$ 17,000,000
U.S. Treasury Bills, 0.040% due April 2, 2015 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]		10.42%
Fair Value	[1],[2]		$ 22,997,976
Face Value	[1],[2]		$ 23,000,000

[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.