Pension and Other Postretirement Benefits - Other Postretirement Benefits (Details) - Other Postretirement Benefit Plan - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2021	Mar. 29, 2020
Pension Benefits
Service cost	$ 13	$ 7
Interest cost	141	256
Amortization of actuarial loss	852	763
Amortization of prior service credit	(836)	(1,056)
Net periodic postretirement benefit cost/(income)	$ 170	$ (30)