Summary of Significant Accounting Policies - Activity in Gold Bullion (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013 oz	Mar. 31, 2012 oz	Dec. 31, 2012 oz
Summary Activity In Gold Bullion [Line Items]
Beginning balance, Ounces	6,999,900	5,498,800	5,498,800
Gold contributed, Ounces	415,600		1,951,200
Gold distributed, Ounces	(590,100)		(435,300)
Gold sold, Ounces	(4,400)		(14,800)
Ending balance, Ounces	6,821,000		6,999,900
Beginning balance, Average Cost	$ 9,315,055	$ 6,572,102	$ 6,572,102
Gold contributed, Average Cost	672,521		3,303,091
Gold distributed, Average Cost	(790,973)		(541,586)
Gold sold, Average Cost	(5,819)		(18,552)
Ending balance, Average Cost	9,190,784		9,315,055
Beginning balance, Fair Value	11,647,783	8,418,739	8,418,739
Gold contributed, Fair Value	672,521		3,303,091
Gold distributed, Fair Value	(941,615)		(697,017)
Gold sold, Fair Value	(7,189)		(24,815)
Adjustment for realized gain, Fair Value	152,012		161,694
Adjustment for unrealized gain (loss) on gold bullion, Fair Value	(621,808)		486,091
Ending balance, Fair Value	10,901,704		11,647,783
Gold distributed, Realized Gain (Loss)	150,642		155,431
Gold sold, Realized Gain (Loss)	1,370	1,636	6,263
Ending balance, Realized Gain (Loss)	$ 152,012		$ 161,694