Employee Benefit Plans - Components Of Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 29, 2020	Mar. 31, 2019
Pension and SERPA Benefits:
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6,806	$ 6,632
Interest cost	19,112	21,371
Expected return on plan assets	(33,764)	(35,581)
Amortization of unrecognized: Prior service credit	(272)	(483)
Amortization of unrecognized: Net loss	16,372	11,128
Net periodic benefit cost	8,254	3,067
Postretirement Healthcare Benefits:
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,201	1,184
Interest cost	2,336	2,938
Expected return on plan assets	(3,467)	(3,507)
Amortization of unrecognized: Prior service credit	(595)	(595)
Amortization of unrecognized: Net loss	123	69
Net periodic benefit cost	$ (402)	$ 89