Quarterly report pursuant to Section 13 or 15(d)

Share-Based Payments - Stock Option Activity (Details)

v3.7.0.1
Share-Based Payments - Stock Option Activity (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense $ 2,064 $ 2,159 $ 4,026 $ 4,111
Employee Stock Option [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense 331 375 699 723
Tax benefit related to share-based expense 121 140 254 269
Unrecognized share-based compensation, net of estimated forfeitures $ 2,281 $ 2,414 $ 2,281 $ 2,414
Weighted average period over which unrecognized compensation will be recognized (years) 2 years 1 month 11 days   2 years 1 month 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% 1.00%
Expected stock price volatility     28.70% 29.00%
Weighted Average Risk Free Interest Rate     2.00% 1.30%
Expected life of options (in years)     6 years 11 days 6 years 11 days
Weighted-average fair value of options (dollars per share)     $ 13 $ 12
Outstanding, beginning of period (in shares) 622   564  
Granted (in shares) 0   118  
Exercised (in shares) (103)   (150)  
Forfeited (in shares) (12)   (25)  
Outstanding, end of period (in shares) 507   507  
Exercisable, end of period (in shares) 282   282  
Outstanding, beginning of period (in dollars per share) $ 42   $ 41  
Grants in Period (in dollars per share) 0   48  
Exercises in Period (in dollars per share) 33   33  
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 $ 3,453   $ 3,453  
Aggregate Intrinsic Value Exercisable, end of period $ 2,466   $ 2,466  
Weighted-average remaining contractual term Outstanding, end of period (in years) 4 years 8 months 11 days   4 years 8 months 11 days  
Weighted-average remaining contractual term Exercisable, end of period (in years) 3 years 6 months 11 days   3 years 6 months 11 days