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Capital Stock - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Capital Unit [Line Items]        
Preferred stock, par value (dollars per share) $ 50 $ 50    
Cumulative preferred nonvoting stock (as a percent) 4.50% 4.50%    
Shares held in treasury (in shares) 23,858,463 24,344,813    
Preferred stock included in Treasury shares at cost line of the Consolidated Balance Sheet $ 297,834 $ 289,254    
Common stock, shares authorized 180,000,000 180,000,000    
Common stock, par value (dollars per share) $ 0 $ 0    
Common stock, shares outstanding 38,222,928 37,736,578    
Stock Issued During Period, Shares, Treasury Stock Reissued 648,164 40,429    
4 1/2% Cumulative Preferred Nonvoting Stock        
Capital Unit [Line Items]        
Preferred stock, shares authorized 100,000      
Preferred stock, par value (dollars per share) $ 50      
Cumulative preferred nonvoting stock (as a percent) 4.50%      
Preferred stock, callable price per share (dollars per share) $ 52.50      
Preferred stock, shares issued 71,340      
Shares held in treasury (in shares) 52,878      
Preferred stock repurchased and subsequently canceled (in shares)     33  
Preferred stock included in Treasury shares at cost line of the Consolidated Balance Sheet $ 1,800      
Treasury purchases (in shares) 0 0    
Second Cumulative Preferred Voting Stock        
Capital Unit [Line Items]        
Preferred stock, shares authorized 1,000,000      
Preferred stock, par value (dollars per share) $ 10      
Preferred stock, shares issued 0 0    
Common Stock        
Capital Unit [Line Items]        
Common stock, shares outstanding 62,081,391 62,081,391 62,081,391 62,081,391
Treasury        
Capital Unit [Line Items]        
Common stock, shares outstanding 23,858,463 24,344,813 24,708,917 24,633,081
Share Repurchase Program, May 2015 | Common Stock        
Capital Unit [Line Items]        
Treasury purchases (in shares) 168,941      
Stock repurchased program, authorized amount (up to) $ 100,000      
Share Repurchase Program, May 2015 | Treasury        
Capital Unit [Line Items]        
Treasury purchases (in shares)   0 150,000