Pension and Other Post-Retirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Pension
Employee benefits
Service cost	$ 846	$ 754
Interest cost	2,833	2,826
Expected return on plan assets	(3,877)	(3,450)
Amortization of prior service credit	(181)	(119)
Amortization of net loss	645	966
Net periodic cost	266	977
Other Postretirement Benefits Plan
Employee benefits
Net periodic cost	$ 0	$ 0