Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Pension Benefits [Member]
Components of net periodic benefit cost (income) [Abstract]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	866	1,443	1,724	2,910
Expected return on plan assets	(1,495)	(2,077)	(2,990)	(4,153)
Amortization of net gain	528	440	988	970
Net periodic benefit income	(101)	(194)	(278)	(273)
Other Benefits [Member]
Components of net periodic benefit cost (income) [Abstract]
Service cost	56	63	117	127
Interest cost	106	153	215	306
Amortization of prior service credit	(58)	(225)	(284)	(451)
Amortization of net gain	(47)	(13)	(100)	(21)
Curtailment gain	(2,591)	0	(2,591)	0
Net periodic benefit income	$ (2,534)	$ (22)	$ (2,643)	$ (39)