Inventories - Inventories, Net of Reserves (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 63,024	$ 60,806
In-process and finished	122,432	116,678
Supplies	77,491	74,580
Total	$ 262,947	$ 252,064