Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2017	Oct. 01, 2016
Pension Benefits [Member]
Components of net periodic benefit cost (income) [Abstract]
Service cost	$ 35	$ 180	$ 106	$ 540
Interest cost	1,659	1,973	4,977	5,917
Expected return on plan assets	(2,184)	(2,466)	(6,552)	(7,398)
Amortization of net (gain) loss	536	760	1,608	2,280
Net periodic benefit income	46	447	139	1,339
Other Benefits [Member]
Components of net periodic benefit cost (income) [Abstract]
Service cost	54	61	163	183
Interest cost	147	153	442	458
Amortization of prior service credit	(225)	(224)	(676)	(672)
Amortization of net (gain) loss	(10)	(9)	(30)	(27)
Net periodic benefit income	$ (34)	$ (19)	$ (101)	$ (58)