Annual report pursuant to Section 13 and 15(d)

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

v3.3.1.900
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, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation $ 7,486 $ 6,681 $ 6,178
Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at beginning of year (shares) 1,363 1,732 2,874
Granted (shares) 96 106 118
Exercise of stock options (in shares) (659) (450) (1,260)
Forfeited (shares) (14) (25)  
Outstanding at end of year (shares) 786 1,363 1,732
Exercisable at end of year 586 1,160 1,514
Weighted Average Outstanding at beginning of year (per share) $ 28 $ 27 $ 26
Weighted average exercise price for options granted in the period 50 43 38
Weighted average exercise price for options exercised in the period 26 28 26
Weighted average exercise price for options forfeited in the period 29 37  
Weighted Average Outstanding at end of year (per share) 32 28 27
Weighted average exercise price for options exercisable at year end 28 26 26
Weighted-average fair value of options granted during the year (dollars per share) $ 15 $ 14 $ 14
Aggregate intrinsic value of options exercised $ 16,191 $ 7,259 $ 15,477
Average aggregate intrinsic value for options outstanding 13,001    
Average aggregate instrinsic value for exercisable options 12,332    
Share-based compensation 1,386 1,302 1,410
Tax benefit related to share-based compensation expense 542 $ 497 $ 508
Unrecognized compensation cost $ 1,728    
Non-employee Director Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at beginning of year (shares) 8 26 29
Exercise of stock options (in shares) (8) (18) (3)
Outstanding at end of year (shares)   8 26
Weighted Average Outstanding at beginning of year (per share) $ 26 $ 23 $ 23
Weighted average exercise price for options exercised in the period $ 26 22 20
Weighted Average Outstanding at end of year (per share)   $ 26 $ 23
Aggregate intrinsic value of options exercised $ 208 $ 412 $ 54
Non-employee Director Activity - Options [Abstract]      
Term of options issued under the plan 10 years    
Exercise Price Range 22.47 thru 22.87 [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at end of year (shares) 326    
Exercisable at end of year 326    
Weighted Average Outstanding at end of year (per share) $ 22.50    
Weighted average exercise price for options exercisable at year end 22.50    
Range of exercise price, lower range limit 22.47    
Range of exercise price, upper range limit $ 22.87    
Weighted average remaining contractual life 1 year 11 days    
Exercise Price Range 24.98 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) 96    
Exercisable at end of year 96    
Weighted Average Outstanding at end of year (per share) $ 28.42    
Weighted average exercise price for options exercisable at year end 28.42    
Range of exercise price, lower range limit 24.98    
Range of exercise price, upper range limit $ 28.61    
Weighted average remaining contractual life 2 years 1 month 11 days    
Exercise Price Range 36.55 thru 38.23 [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at end of year (shares) 160    
Exercisable at end of year 128    
Weighted Average Outstanding at end of year (per share) $ 36.91    
Weighted average exercise price for options exercisable at year end 36.84    
Range of exercise price, lower range limit 36.55    
Range of exercise price, upper range limit $ 38.23    
Weighted average remaining contractual life 3 years 8 months 11 days    
Exercise Price Range 41.80 thru 45.97 [Member] | Employee Stock Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding at end of year (shares) 118    
Exercisable at end of year 36    
Weighted Average Outstanding at end of year (per share) $ 43.22    
Weighted average exercise price for options exercisable at year end 43.13    
Range of exercise price, lower range limit 41.80    
Range of exercise price, upper range limit $ 45.97    
Weighted average remaining contractual life 5 years 3 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    
Weighted Average Outstanding at end of year (per share) $ 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 6 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) 786    
Exercisable at end of year 586    
Weighted Average Outstanding at end of year (per share) $ 32.37    
Weighted average exercise price for options exercisable at year end 27.87    
Range of exercise price, lower range limit 22.47    
Range of exercise price, upper range limit $ 52.03    
Weighted average remaining contractual life 2 years 10 months 11 days