Pension and Other Postretirement Benefits - Other Postretirement Benefits (Details) - Other Postretirement Benefit Plan - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2021	Sep. 27, 2020	Sep. 26, 2021	Sep. 27, 2020
Pension Benefits
Service cost	$ 14	$ 7	$ 40	$ 21
Interest cost	141	257	423	770
Amortization of actuarial loss	851	763	2,555	2,289
Amortization of prior service credit	(837)	(1,099)	(2,509)	(3,378)
Net periodic postretirement benefit cost/(income)	$ 169	$ (72)	$ 509	$ (298)