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FINANCIAL INSTRUMENTS, OFF-BALANCE SHEET RISKS AND CONTINGENCIES (Additional Information) (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Money Market Funds [Member]
Loss Contingencies [Line Items]
Deposits in domestic and foreign financial institutions, including cash investments in money market funds	$ 52,000,000	$ 150,000,000
US Treasury Securities [Member]
Loss Contingencies [Line Items]
Deposits in domestic and foreign financial institutions, including cash investments in money market funds	$ 1,604,935,976	$ 1,841,256,955

X

- Definition

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Details

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