General - Defined Benefit Plan (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 24, 2020	Sep. 30, 2021	Sep. 24, 2020
General
Service cost	$ 278	$ 274	$ 839	$ 821
Interest cost	300	342	901	1,028
Net amortization of prior service cost and actuarial loss	331	248	986	743
Net periodic pension cost	$ 909	$ 864	$ 2,726	$ 2,592