Post-Retirement Health Care (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Retirement Benefits [Abstract]
Service cost	$ 170	$ 213
Interest cost	199	197
Amortization of net (gain) loss	0	37
Net periodic post-retirement benefit cost	$ 369	$ 447