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Commitments and Contingent Liabilities - Operating Leases (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 25, 2016
Dec. 27, 2015
Commitments and Contingencies Disclosure [Abstract]      
Rent expense $ 19,000 $ 16,000 $ 16,000
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]      
2018 10,738    
2019 7,532    
2020 6,153    
2021 4,972    
2022 4,731    
Later years 18,555    
Total minimum lease payments $ 52,681