Summary Of Significant Accounting Policies (Activity In Redeemable Capital Shares) (Details) (USD $) In Thousands, except Share data	3 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011
Summary Of Significant Accounting Policies [Abstract]
Redeemable capital shares, prescribed aggregation	50,000	50,000
Beginning balance, redeemable capital shares	475,050,000	386,950,000
Shares issued, Shares	86,850,000	208,250,000
Shares redeemed, Shares	(22,450,000)	(55,750,000)
Ending balance, redeemable capital Shares	539,450,000	539,450,000
Beginning balance, redeemable capital shares, Amount	$ 6,982,009	$ 5,315,950
Shares issued, Amount	1,409,816	3,139,985
Shares redeemed, Amount	(375,194)	(819,772)
Redemption value adjustment	509,465	889,933
Ending balance, redeemable capital shares, Amount	$ 8,526,096	$ 8,526,096