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Incentive Plans - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Pretax compensation expense $ 15,491,000 $ 17,537,000 $ 19,746,000
Expense provision under cash-based compensation plans 16,118,000 6,938,000 5,080,000
Maximum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares that may be issued 11,900,000    
Performance Shares
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of payment based upon Total Shareholder Return performance prior to 2010 50.00%    
Percentage of payment based upon achievement of established internal financial performance targets prior to 2010 50.00%    
Pretax compensation expense $ 12,151,000 $ 8,879,000 $ 7,562,000
Weighted-average Grant Date Fair Value, Granted   $ 39.38 $ 40.34
Performance Shares | Minimum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Units paid target range 0.00%    
Performance Shares | Maximum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Units paid target range 200.00%    
Stock Options
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award expiration date for share-based compensation plans 10 years subsequent to the grant    
Stock Options | Minimum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share based compensation plans vesting period (in years) 3 years    
Stock Options | Maximum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share based compensation plans vesting period (in years) 5 years