Pension and Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 27, 2016	Mar. 29, 2015
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 998	$ 1,011
Interest cost	4,606	4,605
Expected return on assets	(5,507)	(5,479)
Net amortization and deferrals	2,132	2,201
Net periodic benefit cost	2,229	2,338
Contributions to defined benefit pension plans	370
Expected contributions during the remainder of fiscal year	3,130
Postretirement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	132	150
Interest cost	294	285
Expected return on assets	0	0
Net amortization and deferrals	0	(114)
Net periodic benefit cost	$ 426	$ 321