Summary of Significant Accounting Policies - Activity in Gold Bullion (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013 oz	Jun. 30, 2012	Jun. 30, 2013 oz	Jun. 30, 2012
Summary Activity In Gold Bullion [Line Items]
Beginning balance, Ounces	6,821,000		6,999,900
Gold contributed, Ounces			415,600
Gold distributed, Ounces	(1,060,700)		(1,650,800)
Gold sold, Ounces	(4,100)		(8,500)
Ending balance, Ounces	5,756,200		5,756,200
Beginning balance, Average Cost	$ 9,190,784		$ 9,315,055
Gold contributed, Average Cost			672,521
Gold distributed, Average Cost	(1,429,134)		(2,220,107)
Gold sold, Average Cost	(5,627)		(11,446)
Market value reserve, Average Cost	(894,628)		(894,628)
Ending balance, Average Cost	6,861,395		6,861,395
Beginning balance, Fair Value	10,901,704		11,647,783
Gold contributed, Fair Value			672,521
Gold distributed, Fair Value	(1,483,453)		(2,425,068)
Gold sold, Fair Value	(6,195)		(13,384)
Adjustment for realized gain, Fair Value	54,887		206,899
Adjustment for unrealized loss on gold bullion, Fair Value	(2,605,548)		(3,227,356)
Ending balance, Fair Value	6,861,395		6,861,395
Gold distributed, Realized Gain (Loss)	54,319		204,961
Gold sold, Realized Gain (Loss)	568	1,526	1,938	3,162
Ending balance, Realized Gain (Loss)	$ 54,887		$ 206,899