Summary of Significant Accounting Policies (Activity in Gold Bullion) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 oz	Dec. 31, 2011 oz	Dec. 31, 2010 oz
Summary Activity In Gold Bullion [Line Items]
Beginning balance, Ounces	5,498,800	3,783,000	2,550,400
Gold contributed, Ounces	1,951,200	2,333,900	1,359,300
Gold distributed, Ounces	(435,300)	(606,800)	(117,600)
Gold sold, Ounces	(14,800)	(11,300)	(9,100)
Ending balance, Ounces	6,999,900	5,498,800	3,783,000
Beginning balance, Average Cost	$ 6,572,102	$ 3,568,036	$ 1,914,867
Gold contributed, Average Cost	3,303,091	3,660,287	1,748,964
Gold distributed, Average Cost	(541,586)	(644,033)	(88,442)
Gold sold, Average Cost	(18,552)	(12,188)	(7,353)
Ending balance, Average Cost	9,315,055	6,572,102	3,568,036
Beginning balance, Fair Value	8,418,739	5,317,017	2,793,239
Gold contributed, Fair Value	3,303,091	3,660,287	1,748,964
Gold distributed, Fair Value	(697,017)	(915,939)	(128,153)
Gold sold, Fair Value	(24,815)	(17,758)	(11,051)
Adjustment for realized gain, Fair Value	161,694	277,476	43,409
Adjustment for unrealized gain (loss) on gold bullion, Fair Value	486,091	97,656	870,609
Ending balance, Fair Value	11,647,783	8,418,739	5,317,017
Gold distributed, Realized Gain (Loss)	155,431	271,906	39,711
Gold sold, Realized Gain (Loss)	6,263	5,570	3,698
Ending balance, Realized Gain (Loss)	$ 161,694	$ 277,476	$ 43,409