Statement of Changes in Shareholders Equity (Unaudited) - USD ($)	Total	General Shares [Member]	General Shares [Member] Total Equity [Member]	Shares [Member]	Shares [Member] Total Equity [Member]
Balance, Value at Dec. 31, 2013	$ 234,895,069		$ 671		$ 234,894,398
Balance Shares at Dec. 31, 2013		40		14,000,000
Sale of Shares, Value	153,774,409				153,774,409
Sale of Shares, Shares				9,400,000
Redemption of Shares, Value	(77,298,278)				(77,298,278)
Redemption of Shares, Shares				(4,800,000)
Net Increase (Decrease) due to share transactions, Value	76,476,131				76,476,131
Net Increase (Decrease) due to share transactions, Shares				4,600,000
Net Income (Loss)
Net investment income (loss)	(1,035,773)		(2)		(1,035,771)
Net realized gain (loss) on United States Treasury Obligations and Commodity Futures Contracts	(14,707,548)		(28)		(14,707,520)
Net change in unrealized gain (loss) on United States Treasury Obligations and Commodity Futures Contracts	19,951,855		38		19,951,817
Net Income (Loss)	4,208,534		8		4,208,526
Net Change in Shareholders' Equity, Value	80,684,665		8		80,684,657
Net Change in Shareholders' Equity, Shares				4,600,000
Balance, Value at Jun. 30, 2014	315,579,734		679		315,579,055
Balance, Shares at Jun. 30, 2014		40		18,600,000
Balance, Value at Mar. 31, 2014	304,307,577		634		304,306,943
Balance Shares at Mar. 31, 2014		40		19,200,000
Sale of Shares, Value	49,128,459				49,128,459
Sale of Shares, Shares				3,000,000
Redemption of Shares, Value	(58,029,746)				(58,029,746)
Redemption of Shares, Shares				(3,600,000)
Net Increase (Decrease) due to share transactions, Value	(8,901,287)				(8,901,287)
Net Increase (Decrease) due to share transactions, Shares				(600,000)
Net Income (Loss)
Net investment income (loss)	(550,059)		(1)		(550,058)
Net realized gain (loss) on United States Treasury Obligations and Commodity Futures Contracts	(2,039,502)		(5)		(2,039,497)
Net change in unrealized gain (loss) on United States Treasury Obligations and Commodity Futures Contracts	22,763,005		51		22,762,954
Net Income (Loss)	20,173,444		45		20,173,399
Net Change in Shareholders' Equity, Value	11,272,157		45		11,272,112
Net Change in Shareholders' Equity, Shares				(600,000)
Balance, Value at Jun. 30, 2014	315,579,734		679		315,579,055
Balance, Shares at Jun. 30, 2014		40		18,600,000
Balance, Value at Dec. 31, 2014	220,647,504		640		220,646,864
Balance Shares at Dec. 31, 2014		40		13,800,000
Sale of Shares, Value	130,193,589				130,193,589
Sale of Shares, Shares				8,200,000
Redemption of Shares, Value	(136,638,949)				(136,638,949)
Redemption of Shares, Shares				(9,000,000)
Net Increase (Decrease) due to share transactions, Value	(6,445,360)				(6,445,360)
Net Increase (Decrease) due to share transactions, Shares				(800,000)
Net Income (Loss)
Net investment income (loss)	(813,597)		(2)		(813,595)
Net realized gain (loss) on United States Treasury Obligations and Commodity Futures Contracts	(16,420,885)		(39)		(16,420,846)
Net change in unrealized gain (loss) on United States Treasury Obligations and Commodity Futures Contracts	(9,694,179)		(23)		(9,694,156)
Net Income (Loss)	(26,928,661)		(64)		(26,928,597)
Net Change in Shareholders' Equity, Value	(33,374,021)		(64)		(33,373,957)
Net Change in Shareholders' Equity, Shares				(800,000)
Balance, Value at Jun. 30, 2015	187,273,483		576		187,272,907
Balance, Shares at Jun. 30, 2015		40		13,000,000
Balance, Value at Mar. 31, 2015	203,715,751		608	$ 13,400,000	203,715,143
Balance Shares at Mar. 31, 2015		40
Sale of Shares, Value	85,299,090				85,299,090
Sale of Shares, Shares				5,200,000
Redemption of Shares, Value	(84,517,455)				(84,517,455)
Redemption of Shares, Shares				(5,600,000)
Net Increase (Decrease) due to share transactions, Value	781,635				781,635
Net Increase (Decrease) due to share transactions, Shares				(400,000)
Net Income (Loss)
Net investment income (loss)	(459,848)		(1)		(459,847)
Net realized gain (loss) on United States Treasury Obligations and Commodity Futures Contracts	(2,094,540)		8		(2,094,548)
Net change in unrealized gain (loss) on United States Treasury Obligations and Commodity Futures Contracts	(14,669,515)		(39)		(14,669,476)
Net Income (Loss)	(17,223,903)		(32)		(17,223,871)
Net Change in Shareholders' Equity, Value	(16,442,268)		(32)		(16,442,236)
Net Change in Shareholders' Equity, Shares				(400,000)
Balance, Value at Jun. 30, 2015	$ 187,273,483		$ 576		$ 187,272,907
Balance, Shares at Jun. 30, 2015		40		13,000,000