Financial Highlights (Net Asset Value Based Total Return For A Shareholder) (Details)		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Financial Highlights [Abstract]
Total Return	[1]	1.67%	3.36%	4.18%	7.03%

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