Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2020	Jun. 30, 2019	Jun. 28, 2020	Jun. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Effect of curtailment loss			$ 31
Effect of settlement loss			661	$ 1,547
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,003	$ 962	2,085	1,903
Interest cost	12,549	15,100	25,230	30,043
Expected return on plan assets	(12,227)	(19,232)	(24,807)	(38,329)
Amortization of prior service cost	247	216	497	430
Amortization of net actuarial loss	7,258	9,646	14,134	18,680
Effect of curtailment loss	31	0	31	0
Effect of settlement loss	38	225	661	1,547
Net periodic benefit cost (income)	8,899	6,917	17,831	14,274
Retiree Health and Life Insurance Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	93	78	176	152
Interest cost	81	113	165	231
Expected return on plan assets	(93)	(179)	(183)	(356)
Amortization of prior service cost	(69)	(124)	(137)	(247)
Amortization of net actuarial loss	(215)	(215)	(412)	(408)
Net periodic benefit cost (income)	$ (203)	$ (327)	$ (391)	$ (628)