Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Pension Benefits [Member]
Components of net periodic benefit cost (income) [Abstract]
Service cost	$ 22	$ 35	$ 66	$ 106
Interest cost	1,478	1,659	4,436	4,977
Expected return on plan assets	(2,290)	(2,184)	(6,869)	(6,552)
Amortization of net loss (gain)	293	536	877	1,608
Net periodic benefit (income) cost	(497)	46	(1,490)	139
Other Benefits [Member]
Components of net periodic benefit cost (income) [Abstract]
Service cost	59	54	175	163
Interest cost	147	147	441	442
Amortization of prior service credit	(226)	(225)	(677)	(676)
Amortization of net loss (gain)	14	(10)	43	(30)
Net periodic benefit (income) cost	$ (6)	$ (34)	$ (18)	$ (101)