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FINANCIAL INSTRUMENTS, OFF-BALANCE SHEET RISKS AND CONTINGENCIES (Details) - USD ($)
Sep. 30, 2019
Dec. 31, 2018
Money Market Funds    
Loss Contingencies    
Deposits in domestic and foreign financial institutions, including cash investments in money market funds $ 90,000,000 $ 52,000,000
United States Treasury Obligations    
Loss Contingencies    
Deposits in domestic and foreign financial institutions, including cash investments in money market funds $ 1,405,037,213 $ 1,604,935,976