Summary of Significant Accounting Policies - Summary of Average Monthly Notional Value of Future Contracts Outstanding (Detail) - USD ($)	Mar. 31, 2016	Mar. 31, 2015
Weighted Average [Member] \| Commodity Futures Contract [Member]
Derivative [Line Items]
Average notional market value	$ 160,138,703	$ 161,289,980

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant