Financial Highlights (Net Asset Based Total Return For A Shareholder) (Details)	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Financial Highlights [Abstract]
Total Return before Incentive Fee	6.24%	[1]	(0.31%)	[1]	19.06%	[1]	2.11%	[1]
Incentive Fee	(1.99%)	[1]	0.00%	[1]	(2.75%)	[1]	(0.17%)	[1]
Total Return after Incentive Fee	4.25%	[1]	(0.31%)	[1]	16.31%	[1]	1.94%	[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.