Breakdown of Inventories (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Inventory [Line Items]
Finished goods	$ 353,646	$ 325,762
Raw materials	52,860	57,245
Stores, supplies and other	45,492	45,138
Total inventories	$ 451,998	$ 428,145