Financial Highlights (Net Asset Based Total Return For A Shareholder) (Details)	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Financial Highlights [Abstract]
Total Return	1.82%	[1]	4.25%	[1]	11.57%	[1]	16.31%	[1]

[1] Total return is calculated for all shareholders' equity accounts taken as a whole for each period. Total return is calculated assuming reinvestment of all distributions at shareholders' equity per share during the period.