Counterparty Risk (% Of Total Receivable For Securities Sold) (Details) |
Jun. 30, 2018 |
|---|---|
| Bank of America Securities [Member] | |
| Concentration Risk [Line Items] | |
| % of Total Receivable for Securities Sold | 33.00% |
| Credit Suisse Securities LLC [Member] | |
| Concentration Risk [Line Items] | |
| % of Total Receivable for Securities Sold | 34.00% |
| Wells Fargo Securities [Member] | |
| Concentration Risk [Line Items] | |
| % of Total Receivable for Securities Sold | 16.00% |