Pension and Other Postretirement Benefits - Net Periodic Pension Cost (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended
	Mar. 29, 2020	Mar. 31, 2019
Pension Benefits
Service cost	$ 2,607	$ 1,278
Interest cost	13,390	16,797
Expected return on plan assets	(17,736)	(20,258)
Amortization of actuarial loss	7,176	5,729
Amortization of prior service credit	(486)	(486)
Net periodic postretirement benefit income	4,951	3,060
Qualified Plans
Pension Benefits
Service cost	2,607	1,278
Interest cost	11,742	14,709
Expected return on plan assets	(17,736)	(20,258)
Amortization of actuarial loss	5,655	4,635
Amortization of prior service credit	(486)	(486)
Net periodic postretirement benefit income	1,782	(122)
Pension contributions	2,100	2,000
Expected contributions in 2018	9,000
Non- Qualified Plans
Pension Benefits
Service cost	0	0
Interest cost	1,648	2,088
Expected return on plan assets	0	0
Amortization of actuarial loss	1,521	1,094
Amortization of prior service credit	0	0
Net periodic postretirement benefit income	$ 3,169	$ 3,182