Summary of Significant Accounting Policies - Summary of Average Monthly Notional Value of Future Contracts Outstanding (Detail) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Weighted Average [Member] \| Currency Futures Contracts [Member]
Derivative [Line Items]
Average Notional Value	$ 792,901,625	$ 1,192,701,516	$ 857,795,958	$ 1,192,410,013

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