Financial Highlights (Expense Ratios To Average Equity) (Details)		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Investment Company, Financial Highlights [Abstract]
Operating expenses, before interest expense and other investment related expenses	[1],[2]	(2.76%)	(2.89%)	(2.80%)	(2.88%)
Interest expense and other investment related expenses	[1],[2]	(6.32%)	(3.69%)	(5.69%)	(3.43%)
Total Expenses	[1],[2]	(9.08%)	(6.58%)	(8.49%)	(6.31%)

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

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