Financial Highlights (Expense Ratios To Average Equity) (Details)		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Financial Highlights [Abstract]
Operating expenses, before interest expense and other investment related expenses	[1],[2]	(2.89%)	(2.55%)	(2.88%)	(2.59%)
Interest expense and other investment related expenses	[1],[2]	(3.69%)	(2.34%)	(3.43%)	(2.19%)
Total Expenses	[1],[2]	(6.58%)	(4.89%)	(6.31%)	(4.78%)

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

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