Financial Highlights (Net Asset Value Based Total Return For A Shareholder) (Details)		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Financial Highlights [Abstract]
Total Return	[1]	0.13%	0.49%	(2.25%)	4.69%

[1] Total return is calculated assuming reinvestment of distributions at shareholders' equity per share during the period.