Inventories - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Inventory Disclosure [Abstract]
Terms of precious metals consignment agreements, maximum			1 year
Fees under precious metals consignment agreements	$ 0.7	$ 1.4	$ 2.5	$ 5.0
Fair value of precious metals on hand under consignment agreements	$ 89.5		$ 89.5		$ 112.2