Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Pension Benefits [Member]
Components of net periodic benefit cost (income) [Abstract]
Service cost	$ 20	$ 36	$ 44	$ 71
Interest cost	1,465	1,653	2,958	3,318
Expected return on plan assets	(2,290)	(2,186)	(4,579)	(4,368)
Amortization of net loss (gain)	235	516	584	1,072
Net periodic benefit (income) cost	(570)	19	(993)	93
Other Benefits [Member]
Components of net periodic benefit cost (income) [Abstract]
Service cost	56	53	116	109
Interest cost	146	146	294	295
Amortization of prior service credit	(225)	(226)	(451)	(451)
Amortization of net loss (gain)	11	(15)	29	(20)
Net periodic benefit (income) cost	$ (12)	$ (42)	$ (12)	$ (67)