Pension Plans - Pension plan net periodic benefit costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2021	Jul. 03, 2020	Jul. 02, 2021	Jul. 03, 2020
Defined Benefit Plan Disclosure
Defined Benefit Plan, Service Cost Benefit	$ (1,000)
Increase (Decrease) in PBGC Premium			$ 3,900
Qualified Pension Plan
Defined Benefit Plan Disclosure
Defined Benefit Plan, Service Cost Benefit	(649)
Service cost(1)		$ 1,309	651	$ 2,618
Interest cost on projected benefit obligation	3,558	5,255	7,083	10,510
Expected return on plan assets	(11,314)	(10,796)	(22,589)	(21,592)
Amortization of net loss	1,147	1,201	2,222	2,402
Net pension (income) cost	(7,258)	(3,031)	(12,633)	(6,062)
SERP
Defined Benefit Plan Disclosure
Service cost(1)	0	0	0	0
Interest cost on projected benefit obligation	14	42	29	83
Expected return on plan assets	0	0	0	0
Amortization of net loss	18	236	35	472
Net pension (income) cost	$ 32	$ 278	$ 64	$ 555