Net Asset Value and Financial Highlights - Schedule of Net Asset Value Per Share (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Asset Value
Net asset value per Share, beginning of period	$ 13.35	$ 18.40	$ 25.61
Net realized and change in unrealized gain (loss) on United States Treasury Obligations and Commodity Futures Contracts	2.57	(4.90)	(7.00)
Net investment income (loss)	(0.09)	(0.15)	(0.21)
Net income (loss)	2.48	(5.05)	(7.21)
Net asset value per Share, end of period	15.83	13.35	18.40
Market value per Share, beginning of period	13.37	18.45	25.66
Market value per Share, end of period	$ 15.84	$ 13.37	$ 18.45
Ratio to average Net Assets
Net investment income (loss)	(0.60%)	(0.88%)	(0.84%)
Expenses, after waivers	0.89%	0.90%	0.88%
Expenses, prior to waivers	0.89%	0.90%	0.88%
Total Return, at net asset value	18.58%	(27.45%)	(28.15%)
Total Return, at market value	18.47%	(27.53%)	(28.10%)