Financial Highlights (Net Investment Income Ratio To Average Equity) (Details)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investment Company, Financial Highlights [Abstract]
Net Investment Income (Loss) Ratio	[1]	5.51%	5.22%	8.59%

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