Financial Highlights (Expense Ratios To Average Equity) (Details)		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Financial Highlights [Abstract]
Operating expenses, before interest expense and other investment related expenses	[1]	(2.93%)		(2.69%)		(2.80%)
Ratio Of Incentive Fee To Average Equity	[1]	0.00%		0.00%		(0.21%)
Interest expense and other investment related expenses		(3.56%)	[1]	(2.30%)	[1]	(2.14%)
Total Expenses		(6.49%)	[1]	(4.99%)	[1]	(5.15%)

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