Pension and Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 01, 2017	Sep. 25, 2016	Oct. 01, 2017	Sep. 25, 2016
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 925	$ 1,002	$ 2,798	$ 2,995
Interest cost	4,443	4,611	13,598	13,821
Expected return on assets	(5,896)	(5,512)	(18,057)	(16,523)
Net amortization and deferrals	2,525	2,134	7,738	6,398
Curtailment losses			0	0
Net periodic benefit cost	1,997	2,235	6,077	6,691
Contributions to defined benefit pension plans			26,600
Expected fiscal year defined benefit pension plan contributions			29,000
Postretirement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	172	132	517	397
Interest cost	295	294	885	881
Expected return on assets	0	0	0	0
Net amortization and deferrals	0	0	0	0
Curtailment losses			0	0
Net periodic benefit cost	$ 467	$ 426	$ 1,402	$ 1,278