Pension Plans - Pension plan net periodic benefit costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 03, 2020	Mar. 29, 2019
Qualified Pension Plan
Defined Benefit Plan Disclosure
Service cost	$ 1,309	$ 1,275
Interest cost on projected benefit obligation	5,255	6,606
Expected return on plan assets	(10,796)	(10,640)
Amortization of net loss	1,201	3,815
Net pension (income) cost	(3,031)	1,056
SERP
Defined Benefit Plan Disclosure
Service cost	0	0
Interest cost on projected benefit obligation	41	59
Expected return on plan assets	0	0
Amortization of net loss	236	61
Net pension (income) cost	$ 277	$ 120