Inventories - Inventories, Net of Reserves (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw materials	$ 60,806	$ 66,359
In-process and finished	116,678	112,507
Supplies	74,580	70,803
Total	$ 252,064	$ 249,669