Property, Plant and Equipment ( Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 29, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Gain on disposals of property, plant and equipment		$ (448)	$ 1,142	$ 759
Value added tax (paid from) collected on building sale	$ 700	(707)	694	0
Depreciation, Net From Continuing Operations		$ 14,800	14,300	$ 14,500
Seating
Property, Plant and Equipment [Line Items]
Gain on disposals of property, plant and equipment			$ 1,300