Pension Plans - Pension plan net periodic benefit costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 29, 2019	Mar. 30, 2018
Qualified Pension Plan
Defined Benefit Plan Disclosure
Service cost	$ 1,275	$ 1,224
Interest cost on projected benefit obligation	6,606	5,951
Expected return on plan assets	(10,640)	(11,960)
Amortization of net loss	3,815	2,843
Net pension cost (income)	1,056	(1,942)
SERP
Defined Benefit Plan Disclosure
Service cost	0	0
Interest cost on projected benefit obligation	59	54
Expected return on plan assets	0	0
Amortization of net loss	61	83
Net pension cost (income)	$ 120	$ 137