Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities
Net Income (Loss)	$ 20,881,716	$ (4,005,315)
Adjustments to reconcile net income (loss) to net cash provided by (used for) operating activities:
Cost of securities purchased	(200,851,297)	(189,990,848)
Proceeds from securities sold and matured	133,499,999	192,999,511
Net accretion of discount on United States Treasury Obligations	(84,035)	(8,369)
Net realized (gain) loss on United States Treasury Obligations		(1,424)
Net change in unrealized (gain) loss on United States Treasury Obligations and Commodity Futures Contracts	(31,346)	(7,980,343)
Cash transfer to Commodity Broker to satisfy variation margin requirements (Note 4)		(9,971,010)
Cash received (paid) to Commodity Broker to satisfy open variation margin, net (Note 4)		9,427,018
Change in operating receivables and payables:
Variation margin	(1,188,950)	262,920
Management fee payable	38,896	6,406
Brokerage fee payable	911	(3,010)
Net cash provided by (used for) operating activities	(47,734,106)	(9,264,464)
Cash flows from financing activities
Proceeds from sale of Shares	72,720,422	74,847,261
Redemption of Shares	(14,511,493)	(63,539,406)
Net cash provided by (used for) financing activities	58,208,929	11,307,855
Net change in cash held	10,474,823	2,043,391
Cash at beginning of year	5,341,472	10,651,900
Cash at end of year	15,816,295	$ 12,695,291
Supplemental disclosure of cash flow information:
Cash paid for interest	$ 559