Employee Benefit Plans - Components Of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2021	Sep. 27, 2020	Sep. 26, 2021	Sep. 27, 2020
Pension and SERPA Benefits:
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6,348	$ 6,806	$ 19,044	$ 20,418
Interest cost	15,472	19,112	46,412	57,335
Expected return on plan assets	(32,720)	(33,764)	(98,160)	(101,292)
Amortization of unrecognized: Prior service credit	(312)	(272)	(936)	(816)
Amortization of unrecognized: Net loss	18,386	16,372	55,158	49,116
Settlement loss	0	0	816	0
Net periodic benefit cost	7,174	8,254	22,334	24,761
Postretirement Healthcare Benefits:
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,288	1,202	3,864	3,605
Interest cost	1,626	2,336	4,878	7,008
Expected return on plan assets	(3,495)	(3,467)	(10,485)	(10,401)
Amortization of unrecognized: Prior service credit	(581)	(595)	(1,743)	(1,785)
Amortization of unrecognized: Net loss	264	123	792	369
Net periodic benefit cost	$ (898)	$ (401)	$ (2,694)	$ (1,204)