Net Asset Value and Financial Highlights - Summary of Net Asset Value Per Share (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net Asset Value
Net asset value per Share, beginning of period	$ 15.20	$ 15.85	$ 15.99	$ 16.78
Net realized and change in unrealized gain (loss) from United States Treasury Obligations and Commodity Futures Contracts	(0.76)	1.15	(1.52)	0.25
Net investment income (loss)	(0.03)	(0.03)	(0.06)	(0.06)
Net income (loss)	(0.79)	1.12	(1.58)	0.19
Net asset value per Share, end of period	14.41	16.97	14.41	16.97
Market value per Share, beginning of period	15.17	15.86	15.91	16.84
Market value per Share, end of period	$ 14.40	$ 17.00	$ 14.40	$ 17.00
Ratio to average Net Assets
Net investment income (loss)	(0.83%)	(0.74%)	(0.81%)	(0.73%)
Total expenses	0.82%	0.77%	0.82%	0.77%
Total Return, at net asset value	(5.20%)	7.07%	(9.88%)	1.13%
Total Return, at market value	(5.08%)	7.19%	(9.49%)	0.95%