Inventories - Major Classes of Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 164,925	$ 133,311
Work-in-process	45,054	35,807
Finished goods	142,297	153,377
Gross inventories	352,276	322,495
Excess and obsolete reserves	(30,082)	(25,269)
Net inventories	$ 322,194	$ 297,226