Inventories - Allowance (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Inventory Valuation Reserves [Roll Forward]
Balance, beginning of period	$ 2,350	$ 1,407	$ 1,210	$ 1,118
Provisions for excess and obsolete inventories	(150)	(263)	1,003	55
Inventories written off	0	(30)	(13)	(59)
Balance, end of period	$ 2,200	$ 1,114	$ 2,200	$ 1,114