Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 26, 2021	Jun. 27, 2020	Jun. 26, 2021	Jun. 27, 2020
Pension Benefits [Member]
Components of net periodic benefit cost (income) [Abstract]
Interest cost	$ 313	$ 866	$ 626	$ 1,724
Expected return on plan assets	(904)	(1,495)	(1,808)	(2,990)
Amortization of net loss (gain)	379	528	757	988
Net periodic benefit income	(212)	(101)	(425)	(278)
Other Benefits [Member]
Components of net periodic benefit cost (income) [Abstract]
Interest cost	87	106	174	215
Amortization of net loss (gain)	(33)	(47)	(64)	(100)
Service cost	65	56	130	117
Amortization of prior service credit	(117)	(58)	(235)	(284)
Curtailment gain	0	(2,591)	0	(2,591)
Net periodic benefit income	$ 2	$ (2,534)	$ 5	$ (2,643)