Pension and Other Postretirement Benefits - Pension Benefits - Net Periodic Pension Cost (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2021	Mar. 29, 2020
Pension Benefits
Service cost	$ 2,276	$ 2,607
Interest cost	8,717	13,390
Expected return on plan assets	(12,677)	(17,736)
Amortization of actuarial loss	6,876	7,176
Amortization of prior service credit	(486)	(486)
Net periodic postretirement benefit cost/(income)	4,706	4,951
Qualified Plans
Pension Benefits
Service cost	2,276	2,607
Interest cost	7,629	11,742
Expected return on plan assets	(12,677)	(17,736)
Amortization of actuarial loss	5,055	5,655
Amortization of prior service credit	(486)	(486)
Net periodic postretirement benefit cost/(income)	1,797	1,782
Pension contributions	1,500	2,100
Expected future employer contributions	10,000
Non- Qualified Plans
Pension Benefits
Service cost	0	0
Interest cost	1,088	1,648
Expected return on plan assets	0	0
Amortization of actuarial loss	1,821	1,521
Amortization of prior service credit	0	0
Net periodic postretirement benefit cost/(income)	$ 2,909	$ 3,169