Pension and Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 25, 2016	Sep. 27, 2015	Sep. 25, 2016	Sep. 27, 2015
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1,002	$ 1,006	$ 2,995	$ 3,038
Interest cost	4,611	4,603	13,821	13,827
Expected return on assets	(5,512)	(5,476)	(16,523)	(16,452)
Net amortization and deferrals	2,134	2,202	6,398	6,610
Curtailment losses	0	643	0	781
Net periodic benefit cost	2,235	2,978	6,691	7,804
Contributions to defined benefit pension plans			64,800
Expected contributions during the remainder of fiscal year			350
Postretirement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	132	150	397	450
Interest cost	294	285	881	855
Expected return on assets	0	0	0	0
Net amortization and deferrals	0	(114)	0	(341)
Curtailment losses	0	(3,842)	0	(3,842)
Net periodic benefit cost	$ 426	$ (3,521)	$ 1,278	$ (2,878)