Pension and Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 26, 2016	Jun. 28, 2015	Jun. 26, 2016	Jun. 28, 2015
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 995	$ 1,021	$ 1,993	$ 2,032
Interest cost	4,604	4,619	9,210	9,224
Expected return on assets	(5,504)	(5,497)	(11,011)	(10,976)
Net amortization and deferrals	2,132	2,207	4,264	4,408
Curtailment losses	0	138	0	138
Net periodic benefit cost	2,227	2,488	4,456	4,826
Contributions to defined benefit pension plans			750
Expected contributions during the remainder of fiscal year			2,750
Postretirement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	133	150	265	300
Interest cost	293	285	587	570
Expected return on assets	0	0	0	0
Net amortization and deferrals	0	(114)	0	(228)
Curtailment losses	0	0	0	0
Net periodic benefit cost	$ 426	$ 321	$ 852	$ 642