Quarterly report pursuant to Section 13 or 15(d)

Share-Based Payments - Stock Option Activity (Details)

v3.8.0.1
Share-Based Payments - Stock Option Activity (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense $ 1,939 $ 2,093 $ 5,965 $ 6,204
Employee Stock Option [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense 294 377 993 1,101
Tax benefit related to share-based expense 105 140 354 407
Unrecognized share-based compensation, net of estimated forfeitures $ 1,909 $ 2,036 $ 1,909 $ 2,036
Weighted average period over which unrecognized compensation will be recognized (years) 1 year 10 months 11 days   1 year 10 months 11 days  
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) 1.30%   1.30% 1.00%
Expected stock price volatility 28.70%   28.70% 29.00%
Weighted Average Risk Free Interest Rate 2.00%   2.00% 1.30%
Expected life of options (in years) 6 years 11 days   6 years 11 days 6 years 11 days
Weighted-average fair value of options (dollars per share) $ 14   $ 13 $ 12
Outstanding, beginning of period (in shares) 507   564  
Granted (in shares) 5   123  
Exercised (in shares) (18)   (169)  
Forfeited (in shares) (22)   (46)  
Outstanding, end of period (in shares) 472   472  
Exercisable, end of period (in shares) 255   255  
Outstanding, beginning of period (in dollars per share) $ 44   $ 41  
Grants in Period (in dollars per share) 54   48  
Exercises in Period (in dollars per share) 41   34  
Forfeited in period (in dollars per share) 47   46  
Outstanding, end of period (in dollars per share) 44   44  
Exercisable, end of period (in dollars per share) $ 42   $ 42  
Aggregate Intrinsic Value Outstanding, end of period $ 3,963   $ 3,963  
Aggregate Intrinsic Value Exercisable, end of period $ 2,671   $ 2,671  
Weighted-average remaining contractual term Outstanding, end of period (in years) 4 years 6 months 11 days   4 years 6 months 11 days  
Weighted-average remaining contractual term Exercisable, end of period (in years) 3 years 3 months 11 days   3 years 3 months 11 days