Quarterly report pursuant to Section 13 or 15(d)

Share-Based Payments - Stock Option Activity (Details)

v3.10.0.1
Share-Based Payments - Stock Option Activity (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense $ 2,417 $ 2,064 $ 4,678 $ 4,026
Employee Stock Option [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock option grants expire (in years)     7 years  
Grants, vesting period (in years)     3 years  
Expected dividend yield (in hundredths)     1.10% 1.30%
Expected stock price volatility     24.90% 28.70%
Weighted Average Risk Free Interest Rate     2.60% 2.00%
Expected life of options (in years)     6 years 11 days 6 years 11 days
Weighted-average fair value of options (dollars per share)     $ 15 $ 13
Outstanding, beginning of period (in shares)     440  
Granted (in shares)     86  
Exercised (in shares)     (26)  
Forfeited (in shares)     0  
Outstanding, end of period (in shares) 500   500  
Exercisable, end of period (in shares) 287   287  
Outstanding, beginning of period (in dollars per share)     $ 45  
Grants in Period (in dollars per share)     59  
Exercises in Period (in dollars per share)     42  
Forfeited in period (in dollars per share)     0  
Outstanding, end of period (in dollars per share) $ 47   47  
Exercisable, end of period (in dollars per share) $ 44   $ 44  
Aggregate Intrinsic Value Outstanding, end of period $ 4,985   $ 4,985  
Aggregate Intrinsic Value Exercisable, end of period 3,853   $ 3,853  
Weighted-average remaining contractual term Outstanding, end of period (in years)     4 years 4 months 11 days  
Weighted-average remaining contractual term Exercisable, end of period (in years)     3 years 3 months 11 days  
Share-based compensation expense 346 331 $ 688 $ 699
Tax benefit related to share-based expense     172 254
Unrecognized share-based compensation, net of estimated forfeitures $ 2,243 $ 2,281 $ 2,243 $ 2,281
Weighted average period over which unrecognized compensation will be recognized (years)     2 years 11 days