Service Providers and Related Party Agreements - Additional Information (Detail) - USD ($)		3 Months Ended		6 Months Ended
	Feb. 26, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Related Party Transaction [Line Items]
Management fee percentage per annum of daily net asset				0.75%
Management Fees		$ 416,853	$ 561,302	$ 749,396	$ 1,061,811
Management Fees payable		132,087		132,087		$ 130,925
Brokerage fees		36,246	12,453	66,432	27,473
Brokerage fees payable		4,996		4,996		4,635
United States Treasury Obligations		217,001,291		217,001,291		236,994,724
Cash held with commodity broker		0		0		27,364,752
United States Treasury Obligations transferred to commodity broker	$ 51,994,800
Cash and cash equivalent deposited with custodian		9,893,886		9,893,886
Bank of New York Mellon [Member]
Related Party Transaction [Line Items]
Cash transferred to custodian	31,802,760
United States Treasury Obligations transferred to custodian	$ 155,996,427
Fund assets held by custodian						0
Cash and cash equivalent deposited with custodian		$ 159,900,877		$ 159,900,877
Percentage of cash and cash equivalent deposited with custodian		78.49%		78.49%
Deutsche Bank Securities Inc [Member]
Related Party Transaction [Line Items]
Brokerage fees		$ 36,246	$ 12,453	$ 66,432	$ 27,473
Brokerage fees payable		$ 4,996		$ 4,996		4,635
United States Treasury Obligations						236,994,724
Cash held with commodity broker						$ 27,364,752