Statements of Assets and Liabilities (Unaudited) (Parentheticals) - USD ($)	Sep. 30, 2015	Dec. 31, 2014	[1]
Cost of short-term investments	$ 764,376,245	$ 731,902,394
Cost of short-term investments held at brokers (restricted)	$ 62,559,499	$ 52,852,591
Shares, outstanding (in Shares)	43,900,000	36,850,000
Shares, par value (in Dollars per share)	$ 0	$ 0

[1] Previously reported as "Statements of Financial Condition." Please refer to Note 2A.