Financial Highlights (Expense Ratios To Average Equity) (Details)		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Financial Highlights [Abstract]
Operating expenses, before interest expense and other investment related expenses	[1],[2]	(2.54%)	(2.76%)	(2.60%)	(2.78%)
Interest expense and other investment related expenses	[1],[2]	(2.04%)	(2.32%)	(2.10%)	(2.15%)
Total Expenses	[1],[2]	(4.58%)	(5.08%)	(4.70%)	(4.93%)

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

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