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Share-based Compensation - Additional Information (Detail) (USD $)
1 Months Ended 12 Months Ended
Sep. 30, 2012
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Tax benefit recognized in additional paid-in capital upon vesting of restricted stock awards   $ 1,265,000 $ 614,000 $ 1,770,000
Share Incentive Plan, number of additional shares approved 1,000,000      
Share Incentive Plan, Expiration term 10 years      
Share based compensation expense   633,000    
Deferred compensation arrangement with individual, shares issued   24,000    
Restricted stock award   137,000    
Maximum
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting period   5 years    
Minimum
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting period   3 years    
Restricted Stock
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock awards vested and charged   2,850,000 2,524,000 2,678,000
Total income tax benefit recognized related to restricted stock awards   969,000 986,000 1,044,000
Unrecognized compensation cost related to restricted stock awards   $ 1,200,000    
Compensation cost recognition weighted average period   1 year 2 months 12 days