Summary of Significant Accounting Policies (Activity in Gold Bullion) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012 oz	Sep. 30, 2011	Sep. 30, 2012 oz	Sep. 30, 2011
Summary Activity In Gold Bullion [Line Items]
Beginning balance, Ounces	5,819,200		5,498,800
Gold contributed, Ounces	775,900		1,374,200
Gold distributed, Ounces	(127,100)		(397,900)
Gold sold, Ounces	(3,600)		(10,700)
Ending balance, Ounces	6,464,400		6,464,400
Beginning balance, Average Cost	$ 7,228,945		$ 6,572,102
Gold contributed, Average Cost	1,303,832		2,302,662
Gold distributed, Average Cost	(158,787)		(492,112)
Gold sold, Average Cost	(4,547)		(13,209)
Ending balance, Average Cost	8,369,443		8,369,443
Beginning balance, Fair Value	9,302,094		8,418,739
Gold contributed, Fair Value	1,303,832		2,302,662
Gold distributed, Fair Value	(202,641)		(633,180)
Gold sold, Fair Value	(5,909)		(17,733)
Adjustment for realized gain, Fair Value	45,216		145,592
Adjustment for unrealized gain on gold bullion, Fair Value	1,038,210		1,264,722
Ending balance, Fair Value	11,480,802		11,480,802
Gold distributed, Realized Gain (Loss)	43,854		141,068
Gold sold, Realized Gain (Loss)	1,362	1,619	4,524	3,784
Ending balance, Realized Gain (Loss)	$ 45,216		$ 145,592