Net Asset Value and Financial Highlights - Schedule of Net Asset Value Per Share (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net Asset Value
Net asset value per Share, beginning of period	$ 13.30	$ 17.08	$ 13.35	$ 18.40
Net realized and change in unrealized gain (loss) on United States Treasury Obligations and Commodity Futures Contracts	2.03	0.98	2.00	(0.30)
Net investment income (loss)	(0.02)	(0.04)	(0.04)	(0.08)
Net income (loss)	2.01	0.94	1.96	(0.38)
Net asset value per Share, end of period	15.31	18.02	15.31	18.02
Market value per Share, beginning of period	13.30	17.09	13.37	18.45
Market value per Share, end of period	$ 15.35	$ 18.01	$ 15.35	$ 18.01
Ratio to average Net Assets
Net investment income (loss)	(0.62%)	(0.87%)	(0.66%)	(0.87%)
Total expenses	0.88%	0.88%	0.89%	0.89%
Total Return, at net asset value	15.11%	5.50%	14.68%	(2.07%)
Total Return, at market value	15.41%	5.38%	14.81%	(2.38%)