Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity - Summary of Changes in Shareholders' Equity (Details)

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Shareholders' Equity - Summary of Changes in Shareholders' Equity (Details) - USD ($)
 3 Months Ended 25 Months Ended
Dec. 12, 2017
Mar. 31, 2018
Apr. 01, 2017
Mar. 31, 2018
Jan. 01, 2018
Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Beginning of Period   $ 329,927,000        
Adoption of ASU 2018-02   1,400,000        
Foreign Currency Translation Adjustment   233,000 $ 395,000      
Retirement Liability Adjustment – Net of Tax   215,000 131,000      
Net Income   3,294,000 $ 11,587,000      
End of Period   $ 338,028,000   $ 338,028,000    
Common Stock            
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
End of Period (in shares)   21,431,000   21,431,000    
Convertible Class B Stock            
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
End of Period (in shares)   6,660,000   6,660,000    
COMMON STOCK            
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Beginning of Period   $ 297,000        
Conversion of Class B Shares to Common Shares   0        
Exercise of Stock Options   1,000        
End of Period   $ 298,000   $ 298,000    
COMMON STOCK | Common Stock            
Class of Stock [Line Items]            
Shares Authorized (in shares)   40,000,000   40,000,000    
Share Par Value (in usd per share)   $ 0.01   $ 0.01    
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Beginning of Period (in shares)   22,861,000        
Conversion of Class B Shares to Common Shares (in shares)   226,000        
Exercise of Stock Options (in shares)   19,000        
End of Period (in shares)   23,106,000   23,106,000    
COMMON STOCK | Convertible Class B Stock            
Class of Stock [Line Items]            
Shares Authorized (in shares)   15,000,000   15,000,000    
Share Par Value (in usd per share)   $ 0.01   $ 0.01    
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Beginning of Period (in shares)   6,852,000        
Conversion of Class B Shares to Common Shares (in shares)   (226,000)        
Exercise of Stock Options (in shares)   34,000        
End of Period (in shares)   6,660,000   6,660,000    
ADDITIONAL PAID IN CAPITAL            
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Beginning of Period   $ 67,791,000        
Exercise of Stock Options   159,000        
Stock Compensation Expense   931,000        
End of Period   68,881,000   $ 68,881,000    
ACCUMULATED OTHER COMPREHENSIVE LOSS            
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Beginning of Period   (13,352,000)        
Adoption of ASU 2018-02   (1,373,000)        
Foreign Currency Translation Adjustment   233,000        
Retirement Liability Adjustment – Net of Tax   215,000        
End of Period   (14,277,000)   (14,277,000)    
RETAINED EARNINGS            
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Beginning of Period   325,191,000        
Adoption of ASU 2018-02   1,373,000        
Net Income   3,294,000        
End of Period   333,126,000   $ 333,126,000    
RETAINED EARNINGS | Accounting Standards Update 2014-09            
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Adoption of ASU 2014-09         $ 3,300,000 $ 3,268,000
TREASURY STOCK            
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Beginning of Period   $ (50,000,000)        
Beginning of Period (in shares)   1,675,000        
Purchase $ (50,000,000) $ 0        
Purchase (in shares)   0   (1,675,000)    
End of Period   $ (50,000,000)   $ (50,000,000)    
End of Period (in shares)   1,675,000   1,675,000