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
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Stockholders' Equity $ 270,371 $ 388,857 $ 386,625  
Foreign Currency Translation Adjustments        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Stockholders' Equity (4,468) (7,042)    
Retirement Liability Adjustment        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Stockholders' Equity (11,982) (8,586)    
Retirement Liability Adjustment – Before Tax (14,264) (10,868)    
Retirement Liability Adjustment – Before Tax 2,282 2,282    
Accumulated Other Comprehensive Loss        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Stockholders' Equity $ (16,450) $ (15,628) $ (13,329) $ (13,352)