Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) (Details)

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Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Total Shareholders’ Equity $ 386,625 $ 329,927 $ 337,449  
Foreign Currency Translation Adjustments        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Total Shareholders’ Equity (7,156) (4,465)    
Retirement Liability Adjustment        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Retirement Liability Adjustment – Before Tax (7,814) (12,988)    
Retirement Liability Adjustment – Before Tax 1,641 4,101    
Total Shareholders’ Equity (6,173) (8,887)    
Accumulated Other Comprehensive Loss        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Adoption of ASU 2018-02 1,373      
Total Shareholders’ Equity $ (13,329) $ (13,352) $ (15,494) $ (15,064)