Post-Retirement Health Care (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Retirement Benefits [Abstract]
Service cost	$ 170	$ 213	$ 510	$ 639
Interest cost	199	197	596	591
Amortization of net (gain) loss	0	32	0	95
Net periodic post-retirement benefit cost	$ 369	$ 442	$ 1,106	$ 1,325