Statements of Financial Condition (Unaudited) (Parenthetical) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Investments in Securities, Cost	$ 329,795,281	$ 511,790,491
US Treasury Bill Securities [Member]
Investments in Securities, Cost	232,649,685	409,385,046
Affiliated Investments [Member]
Affiliated Investments, at Cost	$ 97,145,596	$ 102,405,445