Counterparty Risk (% Of Total Receivable For Securities Sold) (Details) |
Sep. 30, 2017 |
|---|---|
| Bank of America Securities [Member] | |
| Concentration Risk [Line Items] | |
| % of Total Receivable for Securities Sold | 29.00% |
| Morgan Stanley [Member] | |
| Concentration Risk [Line Items] | |
| % of Total Receivable for Securities Sold | 23.00% |