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Capital Stock - Narrative (Details) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Capital Unit [Line Items]      
Treasury stock, shares (shares) 23,398,473   23,554,868
Treasury shares, at cost $ 302,673,000   $ 298,143,000
Common stock, shares authorized (shares) 180,000,000    
Common stock, par value (dollars per share) $ 0   $ 0
Common stock, shares, outstanding (shares) 38,682,918   38,526,523
Cumulative Preferred Stock      
Capital Unit [Line Items]      
Preferred stock, shares authorized (shares) 100,000    
Preferred stock, par value (dollars per share) $ 50    
Percentage of cumulative preferred stock (percent) 4.50%    
Preferred stock, callable price per share (dollars per share) $ 52.50    
Preferred stock, shares issued (shares) 71,340    
Treasury stock, shares (shares) 52,878    
Purchase of treasury shares (shares) 0 0  
Second Cumulative Preferred Voting Stock      
Capital Unit [Line Items]      
Preferred stock, shares authorized (shares) 1,000,000    
Preferred stock, par value (dollars per share) $ 10    
Preferred stock, shares issued (shares) 0    
Common Stock      
Capital Unit [Line Items]      
Purchase of treasury shares (shares) 0 0  
Common stock, shares issued (shares)     62,081,391
Stock issued during period, new issues (shares) 0 0  
Common stock, value, issued $ 100,000,000    
Treasury stock      
Capital Unit [Line Items]      
Reissued shares (shares) 230,112 111,902  
Preferred Stock      
Capital Unit [Line Items]      
Preferred stock, par value (dollars per share) $ 50   $ 50
Percentage of cumulative preferred stock (percent) 4.50%   4.50%
Treasury shares, at cost $ 1,800,000