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Employee Benefit Plans Benefit Plan Obligations Compared to Plan Assets (Details) - USD ($)
$ in Thousands
Dec. 26, 2015
Dec. 27, 2014
Pension Plans    
Plans with Accumulated Benefit Obligations in Excess of Plan Assets    
Accumulated benefit obligation $ 275,849 $ 299,127
Fair value of plan assets 253,225 267,026
Other Post-Retirement Benefit Plans    
Plans with Accumulated Benefit Obligations in Excess of Plan Assets    
Accumulated benefit obligation 30,584 29,994
Fair value of plan assets $ 0 $ 0