Post-Retirement Health Care (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Retirement Benefits [Abstract]
Service cost	$ 194	$ 170	$ 583	$ 510
Interest cost	169	199	507	596
Amortization of net loss	5	0	14	0
Net periodic post-retirement benefit cost	$ 368	$ 369	$ 1,104	$ 1,106