Financial Highlights (Expense Ratios To Average Equity) (Details)		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Financial Highlights [Abstract]
Operating expenses, before interest expense and other investment related expenses	[1],[2]	(2.96%)	(2.54%)	(2.88%)	(2.60%)
Interest expense and other investment related expenses	[1],[2]	(3.76%)	(2.04%)	(3.31%)	(2.10%)
Total Expenses	[1],[2]	(6.72%)	(4.58%)	(6.19%)	(4.70%)

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

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