Pension and Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2017	Jun. 26, 2016	Jul. 02, 2017	Jun. 26, 2016
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 921	$ 995	$ 1,873	$ 1,993
Interest cost	4,430	4,604	9,155	9,210
Expected return on assets	(5,880)	(5,504)	(12,161)	(11,011)
Net amortization and deferrals	2,519	2,132	5,213	4,264
Curtailment losses			0	0
Net periodic benefit cost	1,990	2,227	4,080	4,456
Contributions to defined benefit pension plans			1,050
Expected contributions during the remainder of fiscal year			27,550
Postretirement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	173	133	345	265
Interest cost	295	293	590	587
Expected return on assets	0	0	0	0
Net amortization and deferrals	0	0	0	0
Curtailment losses			0	0
Net periodic benefit cost	$ 468	$ 426	$ 935	$ 852