Counterparty Risk (% of Due from Brokers) (Details) |
Dec. 31, 2018 |
|---|---|
| Morgan Stanley [Member] | |
| Concentration Risk [Line Items] | |
| % of Total Due from Brokers | 37.00% |
| J.P. Morgan Securities LLC [Member] | |
| Concentration Risk [Line Items] | |
| % of Total Due from Brokers | 30.00% |