Inventories - Components (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Inventory Disclosure [Abstract]
Raw materials	$ 67,995	$ 57,784
Work in process	4,060	5,957
Finished goods	6,767	8,163
Inventory, gross	78,822	71,904
Less: Allowance for excess and obsolete inventories	(1,210)	(1,118)	$ (1,382)	$ (757)
Total, net	$ 77,612	$ 70,786