Breakdown of Inventories (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Inventory [Line Items]
Finished goods	$ 373,095	$ 311,869
Raw materials	70,025	74,809
Stores, supplies and other	48,810	44,817
Total inventories	$ 491,930	$ 431,495