Financial Highlights (Net Asset Based Total Return For A Shareholder) (Details)	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Financial Highlights [Abstract]
Total Return	7.87%	[1]	8.66%	[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.