Statements of Financial Condition (Parenthetical) - USD ($)	Dec. 31, 2016		Dec. 31, 2015
Investments, cost	$ 271,949,512	[1]	$ 135,975,320
US Treasury Bill Securities [Member]
Investments, cost	$ 252,672,685		$ 135,975,320

[1] Security may be traded on a discount basis. The interest rate shown represents the discount rate at the most recent auction date of the security prior to period end.