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, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Total Shareholders’ Equity $ 337,449 $ 300,225 $ 228,177  
Foreign Currency Translation Adjustments        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Total Shareholders’ Equity (8,597) (7,971)    
Retirement Liability Adjustment        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Retirement Liability Adjustment – Before Tax (10,611) (10,912)    
Retirement Liability Adjustment – Before Tax 3,714 3,819    
Total Shareholders’ Equity (6,897) (7,093)    
Accumulated Other Comprehensive Loss        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Total Shareholders’ Equity $ (15,494) $ (15,064) $ (11,949) $ (3,611)