| Summary of changes in shareholders' equity | 
        
   
   
   
   
   |   | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
     | 
     | 
     | 
   Number of Shares | 
     | 
    
   
   |   | 
     | 
   Amount | 
     | 
     | 
   
Common Stock
 | 
     | 
     | 
   Convertible Class B Stock | 
     | 
    
   
   
   
   |   | 
     | 
     | 
     | 
    
   
   | 
    Shares Authorized 
    | 
     | 
     | 
     | 
     | 
     | 
     | 
   20,000,000 | 
     | 
     | 
     | 
   5,000,000 | 
     | 
    
   
   | 
    Share Par Value 
    | 
     | 
     | 
     | 
     | 
     | 
   $ | 
   0.01 | 
     | 
     | 
   $ | 
   0.01 | 
     | 
    
   
   |   | 
     | 
     | 
     | 
    
   
   | (Dollars in thousands) | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
     | 
     | 
    
   
   | 
    COMMON STOCK 
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    Beginning of Period 
    | 
     | 
   $ | 
   129 | 
     | 
     | 
     | 
   9,680,825 | 
     | 
     | 
     | 
   3,194,229 | 
     | 
    
   
   | 
    Conversion of Class B Shares to Common Shares 
    | 
     | 
     | 
   —   | 
     | 
     | 
     | 
   249,793 | 
     | 
     | 
     | 
   (249,793 | 
   )  | 
    
   
   | 
    Exercise of Stock Options 
    | 
     | 
     | 
   —   | 
     | 
     | 
     | 
   31,431 | 
     | 
     | 
     | 
   18,144 | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
    
   
   | 
    End of Period 
    | 
     | 
   $ | 
   129 | 
     | 
     | 
     | 
   9,962,049 | 
     | 
     | 
     | 
   2,962,580 | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
    
   
   |   | 
     | 
     | 
     | 
    
   
   | 
    ADDITIONAL PAID IN CAPITAL 
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    Beginning of Period 
    | 
     | 
   $ | 
   19,279 | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    Stock Compensation Expense 
    | 
     | 
     | 
   723 | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    Exercise of Stock Options 
    | 
     | 
     | 
   295 | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    End of Period 
    | 
     | 
   $ | 
   20,297 | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
     | 
     | 
    
   
   | 
    ACCUMULATED OTHER COMPREHENSIVE LOSS 
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    Beginning of Period 
    | 
     | 
   $ | 
   (886 | 
   )  | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    Foreign Currency Translation Adjustment 
    | 
     | 
     | 
   (7 | 
   )  | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    Mark to Market Adjustment for Derivatives 
    | 
     | 
     | 
   50 | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    Retirement Liability Adjustment 
    | 
     | 
     | 
   (3,587 | 
   )  | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    End of Period 
    | 
     | 
   $ | 
   (4,430 | 
   )  | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
     | 
     | 
    
   
   | 
    RETAINED EARNINGS 
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    Beginning of Period 
    | 
     | 
   $ | 
   86,622 | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    Net Income 
    | 
     | 
     | 
   11,289 | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    End of Period 
    | 
     | 
   $ | 
   97,911 | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
     | 
     | 
    
   
   | 
    TREASURY STOCK 
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   | 
    Beginning of Period 
    | 
     | 
   $ | 
   (2,281 | 
   )  | 
     | 
     | 
   (178,546 | 
   )  | 
     | 
     | 
   (349,795 | 
   )  | 
    
   
   | 
    Purchase (disposal) 
    | 
     | 
     | 
   —   | 
     | 
     | 
     | 
   —   | 
     | 
     | 
     | 
   —   | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
    
   
   | 
    End of Period 
    | 
     | 
   $ | 
   (2,281 | 
   )  | 
     | 
     | 
   (178,546 | 
   )  | 
     | 
     | 
   (349,795 | 
   )  | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
    
   
   |   | 
     | 
     | 
     | 
    
   
   | 
    TOTAL SHAREHOLDERS’ EQUITY 
    | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
    
   
   | 
    Beginning of Period 
    | 
     | 
   $ | 
   102,863 | 
     | 
     | 
     | 
   9,502,279 | 
     | 
     | 
     | 
   2,844,434 | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
    
   
   |   | 
     | 
     | 
     | 
    
   
   | 
    End of Period 
    | 
     | 
   $ | 
   111,626 | 
     | 
     | 
     | 
   9,783,503 | 
     | 
     | 
     | 
   2,612,785 | 
     | 
    
   
   |   | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
     | 
   
      
    | 
   
      
    | 
     | 
    
   
    
 |