Annual report pursuant to Section 13 and 15(d)

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

v3.10.0.1
Shareholders' Equity, Stock Options and Net Income per Share - Employee Activity - Performance Shares (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Employee Activity - Performance Shares [Line Items]      
Share-based compensation $ 10,549 $ 8,103 $ 8,334
Key Employee Performance Share Based Plan [Member]      
Employee Activity - Performance Shares [Line Items]      
Share-based awards, vesting period 3 years    
Minimum percentage of peer group by which Company share price must outperform before incremental performance shares are issued 25.00%    
Percentage of Peer Group By Which Company Share Price Must Outperform Before Maximum Incremental Shares Are Issued 90.00%    
Outstanding at beginning of year (shares) 69 80 77
Granted (shares) 18 27 29
Additional shares awarded based on performance     7
Vested (shares)     (33)
Forfeited (shares) (22) (38)  
Outstanding at end of year (shares) 65 69 80
Weighted average grant date fair value of non-vested shares at beginning of year $ 58 $ 55 $ 52
Weighted average fair value of performance shares 72 56 49
Stock Issued During Period, Weighted Average Grant Date Fair Value     40
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value     40
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value 67 51  
Weighted average grant date fair value non-vested shares at end of year $ 58 $ 58 $ 55
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value $ 3,795 $ 3,980 $ 4,373
Share-based compensation 1,263 1,045 1,447
Tax benefit related to share-based compensation expense 318 $ 371 $ 537
Unrecognized compensation cost $ 1,415    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 1 year 8 months 11 days