Financial Highlights (Expense Ratios To Average Equity) (Details)		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Investment Company, Financial Highlights [Abstract]
Operating expenses, before interest expense and other investment related expenses	[1],[2]	(2.67%)	(2.83%)
Interest expense and other investment related expenses	[1],[2]	(9.56%)	(4.70%)
Total Expenses	[1],[2]	(12.23%)	(7.53%)

[1] Average equity is calculated using month end values.

[2] Includes all items of income and expense on an annualized basis.