Financial Highlights - Schedule of Net Asset Value Per Share (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net Asset Value
Net asset value per Share, beginning of period	$ 18.17	$ 16.38	$ 19.39	$ 14.95
Net realized and change in unrealized gain (loss) on United States Treasury Obligations, Affiliated Investments and Commodity Futures Contracts	(0.58)	(0.07)	(1.82)	1.38
Net investment income (loss)	0.04	0.00	0.06	(0.02)
Net income (loss)	(0.54)	(0.07)	(1.76)	1.36
Net asset value per Share, end of period	17.63	16.31	17.63	16.31
Market value per Share, beginning of period	18.20	16.39	19.43	14.91
Market value per Share, end of period	$ 17.61	$ 16.38	$ 17.61	$ 16.38
Ratio to average Net Assets
Net investment income (loss)	0.86%	(0.14%)	0.69%	(0.23%)
Expenses, after waivers	0.74%	0.75%	0.76%	0.76%
Expenses, prior to waivers	0.75%	0.77%	0.77%	0.77%
Total Return, at net asset value	(2.97%)	(0.43%)	(9.08%)	9.10%
Total Return, at market value	(3.24%)	(0.06%)	(9.37%)	9.86%