Financial Highlights (Expense Ratios To Average Equity) (Details)		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Investment Company, Financial Highlights [Abstract]
Operating expenses, before interest expense and other investment related expenses	[1],[2]	(2.70%)	(2.76%)	(2.79%)	(2.80%)
Incentive fee	[1],[2]	(0.07%)	(0.00%)	(0.12%)	(0.00%)
Interest expense and other investment related expenses	[1],[2]	(12.97%)	(6.32%)	(11.26%)	(5.69%)
Total Expenses	[1],[2]	(15.74%)	(9.08%)	(14.17%)	(8.49%)

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

[2] Ratios are annualized except for the incentive fee which is not annualized.