Annual report pursuant to Section 13 and 15(d)

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

v3.6.0.2
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, 2016
Dec. 31, 2015
Dec. 31, 2014
Employee Activity - Performance Shares [Line Items]      
Share-based compensation $ 8,334 $ 7,486 $ 6,681
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 30.00%    
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) 77 74 88
Granted (shares) 29 27 23
Additional shares awarded based on performance 7   19
Vested (shares) (33) (24) (56)
Outstanding at end of year (shares) 80 77 74
Weighted average grant date fair value of non-vested shares at beginning of year $ 52 $ 44 $ 37
Weighted average fair value of performance shares 49 67 48
Stock Issued During Period, Weighted Average Grant Date Fair Value 40   30
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value 40 45 30
Weighted average grant date fair value non-vested shares at end of year $ 55 $ 52 $ 44
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value $ 4,373 $ 4,016 $ 3,279
Share-based compensation 1,447 1,308 1,098
Tax benefit related to share-based compensation expense 537 $ 512 $ 419
Unrecognized compensation cost $ 1,709    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 1 year 8 months 11 days