Quarterly report pursuant to Section 13 or 15(d)

Accumulated Other Comprehensive Loss and Other Comprehensive Income - Components of Accumulated Other Comprehensive Loss (Details)

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Accumulated Other Comprehensive Loss and Other Comprehensive Income - Components of Accumulated Other Comprehensive Loss (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Mar. 31, 2018
Jun. 30, 2018
Jul. 01, 2017
Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Total Shareholders’ Equity   $ 351,290   $ 329,927
Adoption of ASU 2018-02 $ 1,400      
Foreign Currency Translation Adjustments        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Total Shareholders’ Equity   (6,037)   (4,465)
Retirement Liability Adjustment        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Total Shareholders’ Equity   (9,830)   (8,887)
Retirement Liability Adjustment – Before Tax   (12,443)   (12,988)
Tax Benefit of Retirement Liability Adjustment   3,986   4,101
Adoption of ASU 2018-02   (1,373) $ 0  
Accumulated Other Comprehensive Loss        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Total Shareholders’ Equity   (15,867)   $ (13,352)
Adoption of ASU 2018-02   $ (1,373)