Counterparty Risk (% Of Total Receivable For Securities Sold) (Details)	Dec. 31, 2017
Bank of America Securities [Member]
Concentration Risk [Line Items]
% of Total Receivable for Securities Sold	28.00%
Nomura Securities International Inc. [Member]
Concentration Risk [Line Items]
% of Total Receivable for Securities Sold	26.00%

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.

No definition available.

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