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Stock-Based Compensation Plans - Additional Information (Detail) (USD $)
 12 Months Ended 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2012
Restricted Stock
Dec. 31, 2011
Restricted Stock
Dec. 31, 2010
Restricted Stock
Jan. 31, 2013
Restricted Stock
Subsequent Event
Jan. 31, 2013
Restricted Stock
Employees
Subsequent Event
Jan. 31, 2013
Restricted Stock
Outside Directors
Subsequent Event
Dec. 31, 2012
Restricted Stock
Minimum
Dec. 31, 2011
Restricted Stock
Minimum
Dec. 31, 2010
Restricted Stock
Minimum
Jan. 31, 2013
Restricted Stock
Minimum
Subsequent Event
Dec. 31, 2012
Restricted Stock
Maximum
Dec. 31, 2011
Restricted Stock
Maximum
Dec. 31, 2010
Restricted Stock
Maximum
Jan. 31, 2013
Restricted Stock
Maximum
Subsequent Event
Dec. 31, 1996
1996 Incentive Plan
Dec. 31, 1997
1997 Incentive Plan
Dec. 31, 1999
1999 Incentive Plan
Dec. 31, 2007
Two Thousand Two Stock Incentive Plan
Dec. 31, 2003
Two Thousand Two Stock Incentive Plan
Dec. 31, 2002
Two Thousand Two Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                              
Shares reserved under long-term incentive plan                                   1,800,000 600,000 2,400,000     2,400,000
Share Based Compensation, additional shares reserved                                         1,000,000 2,000,000  
Restricted stock vesting period                   3 years 3 years 3 years 3 years 5 years 5 years 5 years 5 years            
Shares available for future grant 1,225,923                                            
Compensation expense related to share-based compensation plans $ 6,539,000 $ 4,788,000 $ 3,576,000                                        
Compensation expense related to share-based compensation plans, et tax 4,000,000 3,000,000 2,200,000                                        
Total intrinsic value of options exercised 1,200,000 1,100,000 900,000                                        
Proceeds from stock options exercised 69,000 86,000 46,000                                        
Tax benefit from stock options exercised 500,000 700,000 300,000                                        
Total fair value of restricted shares vested 5,400,000 4,700,000 4,500,000                                        
Unrecognized compensation cost related to non-vested share-based compensation $ 15,500,000                                            
Unrecognized compensation cost weighted average period recognized (years) 2 years 10 months 6 days                                            
Restricted stock grants 296,017     296,017 258,284 240,094   258,008 20,000                            
Restricted stock grants, Weighted average grant date fair value $ 32.62     $ 32.62 $ 35.27 $ 27.36 $ 34.35