Financial Highlights (Net Asset Based Total Return For A Shareholder) (Details)	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Financial Highlights [Abstract]
Total Return	1.57%	[1]	2.68%	[1]	9.57%	[1]	11.57%	[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.