Inventories - Components (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 74,950		$ 67,995
Work in process	2,271		4,060
Finished goods	5,602		6,767
Total, gross	82,823		78,822
Less: Allowance for excess and obsolete inventories	(2,200)	$ (2,350)	(1,210)	$ (1,114)	$ (1,407)	$ (1,118)
Total, net	$ 80,623		$ 77,612