Employee Benefit Plans - Components Of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2021	Mar. 29, 2020
Pension and SERPA Benefits:
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6,348	$ 6,806
Interest cost	15,470	19,112
Expected return on plan assets	(32,720)	(33,764)
Amortization of unrecognized: Prior service credit	(312)	(272)
Amortization of unrecognized: Net loss	18,386	16,372
Settlement loss	816	0
Net periodic benefit cost	7,988	8,254
Postretirement Healthcare Benefits:
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,288	1,201
Interest cost	1,626	2,336
Expected return on plan assets	(3,495)	(3,467)
Amortization of unrecognized: Prior service credit	(581)	(595)
Amortization of unrecognized: Net loss	264	123
Net periodic benefit cost	$ (898)	$ (402)