Financial Highlights (Expense Ratios To Average Equity) (Details)	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Financial Highlights [Abstract]
Operating expenses before incentive fee, interest expense, and other investment related expenses	(2.81%)	[1]	(2.97%)	[1]	(2.79%)	[1]	(3.04%)	[1]
Ratio Of Incentive Fee To Average Equity	(0.20%)	[1]	(0.58%)	[1]	(0.58%)	[1]	(0.59%)	[1]
Interest expense and other investment related expenses	(2.01%)	[1]	(2.02%)	[1]	(1.83%)	[1]	(1.98%)	[1]
Total Expenses	(5.02%)	[1]	(5.57%)	[1]	(5.20%)	[1]	(5.61%)	[1]

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