Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2020	Sep. 29, 2019	Sep. 27, 2020	Sep. 29, 2019
Defined Benefit Plan Disclosure [Line Items]
Effect of curtailment loss			$ 31
Effect of settlement loss			661	$ 2,343
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 881	$ 1,006	2,966	2,909
Interest cost	12,785	13,686	38,015	43,729
Expected return on plan assets	(12,427)	(13,114)	(37,234)	(51,443)
Amortization of prior service cost	245	241	742	671
Amortization of net actuarial loss	7,136	5,993	21,270	24,673
Effect of curtailment loss	0	0	31	0
Effect of settlement loss	0	796	661	2,343
Net periodic benefit cost (income)	8,620	8,608	26,451	22,882
Retiree Health and Life Insurance Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	89	77	265	229
Interest cost	84	116	249	347
Expected return on plan assets	(92)	(179)	(275)	(535)
Amortization of prior service cost	(70)	(124)	(207)	(371)
Amortization of net actuarial loss	(208)	(205)	(620)	(613)
Net periodic benefit cost (income)	$ (197)	$ (315)	$ (588)	$ (943)