Summary of Significant Accounting Policies - Summary of the Tiered Valuation Input Levels (Detail) - USD ($)	Mar. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
United States Treasury Obligations	$ 91,977,743	[1]	$ 135,984,580	[1]	$ 236,994,724
Commodity Futures Contracts	5,498,831		(13,891,219)
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity Futures Contracts	5,498,831		(13,891,219)
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
United States Treasury Obligations	$ 91,977,743		$ 135,984,580

[1] $63,484,032 and $33,225,157, respectively is restricted for maintenance margin purposes