Quarterly report pursuant to Section 13 or 15(d)

Share-Based Payments - Stock Option Activity (Details)

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Share-Based Payments - Stock Option Activity (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense $ 1,677 $ 1,536 $ 3,329 $ 3,094
Employee Stock Option [Member]
        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense 331 324 646 747
Tax benefit related to share-based expense 126 122 246 258
Unrecognized share-based compensation, net of estimated forfeitures 2,314 2,164 2,314 2,164
Employee activity - stock options [Abstract]        
Stock option grants expire (in years)     7 years  
Grants, vesting period (in years)     3 years  
Expected dividend yield (in hundredths) 1.20%   1.20% 1.20%
Expected stock price volatility 31.60%   38.80% 43.70%
Weighted Average Risk Free Interest Rate 1.50%   1.60% 0.90%
Expected life of options (in years) 4 years 6 months 11 days   5 years 3 months 11 days 5 years 3 months 11 days
Weighted-average fair value of options (dollars per share) $ 11   $ 14 $ 13
Outstanding, beginning of period (in shares) 1,474,000   1,732,000  
Granted (in shares) 10,000   101,000  
Exercised (in shares) (53,000)   (394,000)  
Forfeited (in shares) 0   (8,000)  
Outstanding, end of period (in shares) 1,431,000   1,431,000  
Exercisable, end of period (in shares) 1,224,000   1,224,000  
Outstanding, beginning of period (in dollars per share) $ 28   $ 27  
Grants in Period (in dollars per share) $ 45   $ 43  
Exercises in Period (in dollars per share) $ 29   $ 28  
Forfeited in period (in dollars per share) $ 0   $ 38  
Outstanding, end of period (in dollars per share) $ 28   $ 28  
Exercisable, end of period (in dollars per share) $ 26   $ 26  
Aggregate Intrinsic Value Outstanding, end of period 23,931   23,931  
Aggregate Intrinsic Value Exercisable, end of period $ 22,942   $ 22,942  
Weighted-average remaining contractual term Outstanding, end of period (in years) 2 years 7 months 11 days   2 years 7 months 11 days  
Weighted-average remaining contractual term Exercisable, end of period (in years) 2 years 0 months 11 days   2 years 0 months 11 days  
Non-employee Director Stock Options [Member]
        
Employee activity - stock options [Abstract]        
Outstanding, end of period (in shares) 7,500   7,500  
Exercisable, end of period (in dollars per share) $ 26   $ 26  
Weighted-average remaining contractual term Outstanding, end of period (in years)     10 months 11 days  
Non-employee Director Activity - Options [Abstract]        
Terms of options granted to non-employee directors (in years)     10 years