Summary Of Significant Accounting Policies (Activity In Redeemable Capital Shares) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Summary Of Significant Accounting Policies [Abstract]
Redeemable capital shares, prescribed aggregations	50,000
Beginning balance, redeemable capital, Shares	310,700,000	221,250,000	152,000,000
Shares issued, Shares	89,600,000	110,550,000	94,500,000
Shares redeemed, Shares	(41,100,000)	(21,100,000)	(25,250,000)
Ending balance, redeemable capital, Shares	359,200,000	310,700,000	221,250,000
Beginning balance, redeemable capital shares, Amount	$ 5,183,154	$ 2,355,598	$ 2,224,932
Shares issued, Amount	2,040,507	1,575,673	1,438,131
Shares redeemed, Amount	(836,960)	(297,947)	(316,791)
Redemption value adjustment, Amount	4,364,293	1,549,830	(990,674)
Ending balance, redeemable capital shares, Amount	$ 10,750,994	$ 5,183,154	$ 2,355,598