Schedule of Investments (Unaudited) - Treasury Bills - USD ($)		Mar. 31, 2016		Dec. 31, 2015
Schedule Of Investments [Line Items]
Fair Value	[1]	$ 200,955,950		$ 133,489,271
Face Value		$ 217,835,700		$ 138,855,680
U.S. Treasury Bills, 0.275% due April 7, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[2],[3]	13.77%
Fair Value	[2],[3]	$ 29,999,460
Face Value	[2],[3]	$ 30,000,000
U.S. Treasury Bills, 0.270% due April 21, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[3]	3.21%
Fair Value	[3]	$ 6,999,615
Face Value	[3]	$ 7,000,000
U.S. Treasury Bills, 0.200% due April 28, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[3]	17.90%
Fair Value	[3]	$ 38,995,164
Face Value	[3]	$ 39,000,000
U.S. Treasury Bills, 0.325% due June 2, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[3]	50.02%
Fair Value	[3]	$ 108,971,551
Face Value	[3]	$ 109,000,000
U.S. Treasury Bills, 0.235% due July 7, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[2],[3]	7.34%
Fair Value	[2],[3]	$ 15,990,160
Face Value	[2],[3]	$ 16,000,000
United States Treasury Obligations [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity		92.24%	[3]	96.20%	[4]
Fair Value		$ 200,955,950	[3]	$ 133,489,271	[4]
U.S. Treasury Bills, 0.205% due January 14, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[4]			25.22%
Fair Value	[4]			$ 34,999,020
Face Value	[4]			$ 35,000,000
U.S. Treasury Bills, 0.195% due January 21, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[4]			5.05%
Fair Value	[4]			$ 6,999,713
Face Value	[4]			$ 7,000,000
U.S. Treasury Bills, 0.170% due January 28, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[4]			25.22%
Fair Value	[4]			$ 34,997,130
Face Value	[4]			$ 35,000,000
U.S. Treasury Bills, 0.200% due February 4, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[4]			13.69%
Fair Value	[4]			$ 18,998,518
Face Value	[4]			$ 19,000,000
U.S. Treasury Bills, 0.135% due February 11, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[4]			2.16%
Fair Value	[4]			$ 2,999,604
Face Value	[4]			$ 3,000,000
U.S. Treasury Bills, 0.145% due February 18, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[4]			10.45%
Fair Value	[4]			$ 14,498,086
Face Value	[4]			$ 14,500,000
U.S. Treasury Bills, 0.140% due February 25, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[4]			4.32%
Fair Value	[4]			$ 5,999,412
Face Value	[4]			$ 6,000,000
U.S. Treasury Bills, 0.215% due March 3, 2016 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders’ Equity	[4]			10.09%
Fair Value	[4]			$ 13,997,788
Face Value	[4]			$ 14,000,000

[1] $34,994,000 and $24,997,500, respectively is restricted for maintenance margin purposes.

[2] All or a portion of United States Treasury Obligations are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.

[3] 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.

[4] (a)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 year end. (b)A portion of United States Treasury Obligations are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.