Financial Highlights (Net Asset Based Total Return For A Shareholder) (Details)	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Financial Highlights [Abstract]
Total Return before Incentive Fee	3.28%	[1]	(0.37%)	[1]	12.22%	[1]	2.42%	[1]
Incentive Fee	(0.60%)	[1]	0.00%	[1]	(0.65%)	[1]	(0.16%)	[1]
Total Return after Incentive Fee	2.68%	[1]	(0.37%)	[1]	11.57%	[1]	2.26%	[1]

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