Pension and Other Postretirement Benefits - Other Postretirement Benefits (Details) - Other Postretirement Benefit Plan - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2020	Sep. 29, 2019	Sep. 27, 2020	Sep. 29, 2019
Pension Benefits
Service cost	$ 7	$ 6	$ 21	$ 20
Interest cost	257	402	770	1,202
Amortization of actuarial loss	763	843	2,289	2,531
Amortization of prior service credit	(1,099)	(1,192)	(3,378)	(3,574)
Net periodic postretirement benefit income/cost	$ (72)	$ 59	$ (298)	$ 179