Inventories (Allowance) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Inventory Valuation Reserves [Roll Forward]
Balance, beginning of period	$ 1,118	$ 1,382
Provisions for excess and obsolete inventories	101	60
Inventories written off	(10)	0
Balance, end of period	$ 1,209	$ 1,442