Derivative Instruments - Summary of Average Monthly Notional Value of Future Contracts Outstanding (Detail) - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Weighted Average [Member] \| Commodity Futures Contract [Member]
Derivative [Line Items]
Average Notional Value	$ 1,882,782,360	$ 2,526,064,123

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration