Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity, Stock Options and Net Income per Share - Stock Option Activity (Details)

v3.6.0.2
Shareholders' Equity, Stock Options and Net Income per Share - Stock Option Activity (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation $ 8,334 $ 7,486 $ 6,681
Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at beginning of year (shares) 786 1,363 1,732
Granted (shares) 137 96 106
Exercise of stock options (in shares) (346) (659) (450)
Forfeited (shares) (13) (14) (25)
Outstanding at end of year (shares) 564 786 1,363
Exercisable at end of year 331 586 1,160
Weighted Average Outstanding at beginning of year (per share) $ 32 $ 28 $ 27
Weighted average exercise price for options granted in the period 44 50 43
Weighted average exercise price for options exercised in the period 24 26 28
Weighted average exercise price for options forfeited in the period 35 29 37
Weighted Average Outstanding at end of year (per share) 41 32 28
Weighted average exercise price for options exercisable at year end 37 28 26
Weighted-average fair value of options granted during the year (dollars per share) $ 12 $ 15 $ 14
Aggregate intrinsic value of options exercised $ 7,803 $ 16,191 $ 7,259
Average aggregate intrinsic value for options outstanding 2,305    
Average aggregate instrinsic value for exercisable options 2,516    
Share-based compensation 1,473 1,386 1,302
Tax benefit related to share-based compensation expense 546 $ 542 $ 497
Unrecognized compensation cost $ 1,784    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 1 year 9 months 11 days    
Non-employee Director Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at beginning of year (shares) 0 8 26
Exercise of stock options (in shares)   (8) (18)
Outstanding at end of year (shares)   0 8
Weighted Average Outstanding at beginning of year (per share) $ 0 $ 26 $ 23
Weighted average exercise price for options exercised in the period   26 22
Weighted Average Outstanding at end of year (per share)   $ 0 $ 26
Aggregate intrinsic value of options exercised   $ 208 $ 412
Term of options issued under the plan 10 years    
Exercise Price Range 22.47 thru 22.47 [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at end of year (shares) 14    
Exercisable at end of year 14    
Weighted Average Outstanding at end of year (per share) $ 22.47    
Weighted average exercise price for options exercisable at year end 22.47    
Range of exercise price, lower range limit 22.47    
Range of exercise price, upper range limit $ 22.47    
Weighted average remaining contractual life 1 month 12 days    
Exercise Price Range 28.61 thru 28.61 [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at end of year (shares) 76    
Exercisable at end of year 76    
Weighted Average Outstanding at end of year (per share) $ 28.61    
Weighted average exercise price for options exercisable at year end 28.61    
Range of exercise price, lower range limit 28.61    
Range of exercise price, upper range limit $ 28.61    
Weighted average remaining contractual life 1 year 1 month 11 days    
Exercise Price Range 36.55 thru 37.14 [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at end of year (shares) 138    
Exercisable at end of year 138    
Weighted Average Outstanding at end of year (per share) $ 36.87    
Weighted average exercise price for options exercisable at year end 36.87    
Range of exercise price, lower range limit 36.55    
Range of exercise price, upper range limit $ 37.14    
Weighted average remaining contractual life 2 years 7 months 11 days    
Exercise Price Range 41.32 thru 43.67 [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at end of year (shares) 210    
Exercisable at end of year 56    
Weighted Average Outstanding at end of year (per share) $ 43.15    
Weighted average exercise price for options exercisable at year end 42.48    
Range of exercise price, lower range limit 41.32    
Range of exercise price, upper range limit $ 43.67    
Weighted average remaining contractual life 5 years 3 months 11 days    
Exercise Price Range 44.49 thru 48.32 [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at end of year (shares) 40    
Exercisable at end of year 18    
Weighted Average Outstanding at end of year (per share) $ 45.93    
Weighted average exercise price for options exercisable at year end 45.20    
Range of exercise price, lower range limit 44.49    
Range of exercise price, upper range limit $ 48.32    
Weighted average remaining contractual life 5 years 2 months 11 days    
Exercise Price Range 50.71 thru 52.03 [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at end of year (shares) 86    
Exercisable at end of year 29    
Weighted Average Outstanding at end of year (per share) $ 50.79    
Weighted average exercise price for options exercisable at year end 50.79    
Range of exercise price, lower range limit 50.71    
Range of exercise price, upper range limit $ 52.03    
Weighted average remaining contractual life 5 years 1 month 11 days    
Exercise Price Range 22.47 thru 52.03 [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at end of year (shares) 564    
Exercisable at end of year 331    
Weighted Average Outstanding at end of year (per share) $ 40.52    
Weighted average exercise price for options exercisable at year end 37.00    
Range of exercise price, lower range limit 22.47    
Range of exercise price, upper range limit $ 52.03    
Weighted average remaining contractual life 3 years 10 months 11 days