Financial Highlights (Expense Ratios To Average Equity) (Details)		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Financial Highlights [Abstract]
Operating expenses, before interest expense and other investment related expenses	[1],[2]	(2.83%)	(2.82%)
Interest expense and other investment related expenses	[1],[2]	(4.70%)	(2.90%)
Total Expenses	[1],[2]	(7.53%)	(5.72%)

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

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