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Net Periodic Pension Cost (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 29, 2018
Sep. 30, 2017
Sep. 29, 2018
Sep. 30, 2017
Retirement Benefits [Abstract]        
Service cost $ 133 $ 133 $ 399 $ 499
Interest cost on projected benefit obligation 963 1,153 2,889 3,509
Expected return on plan assets (1,327) (1,684) (3,981) (4,852)
Amortization of unrecognized loss 271 260 813 796
Net periodic pension cost (benefit) $ 40 $ (138) $ 120 $ (48)