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Employee Benefit Plans (Components of Net Period Benefit Cost) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 26, 2015
Dec. 27, 2014
Dec. 28, 2013
Pension Plans      
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 3,437 $ 3,397 $ 3,368
Interest cost 11,912 12,822 11,273
Expected return on plan assets (16,987) (17,444) (14,672)
Amortization of prior service cost (credit) (581) 961 2,711
Amortization of net loss (gain) 2,929 (637) (603)
Net periodic cost (benefit) 710 (901) 2,077
Other Post-Retirement Benefit Plans      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 856 758 643
Interest cost 1,062 1,009 708
Expected return on plan assets 0 0 0
Amortization of prior service cost (credit) 0 250 249
Amortization of net loss (gain) 269 660 660
Net periodic cost (benefit) $ 2,187 $ 2,677 $ 2,260