Annual report pursuant to Section 13 and 15(d)

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

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Shareholders' Equity, Stock Options and Net Income per Share - Employee Activity Non-vested Shares (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation $ 11,907 $ 10,549 $ 8,103
Employee Non-vested Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based awards, vesting period 3 years    
Outstanding at beginning of year (shares) 315 227 222
Granted (shares) 117 202 126
Vested (shares) (131) (107) (105)
Forfeited (shares) (24) (7) (16)
Outstanding at end of year (shares) 277 315 227
Weighted average grant date fair value of non-vested shares at beginning of year $ 55 $ 47 $ 45
Weighted Average Grant Date Fair Value 59 60 48
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value 61 56 45
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period, Weighted Average Grant Date Fair Value 57 52 47
Weighted average grant date fair value non-vested shares at end of year $ 58 $ 55 $ 47
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value $ 16,181 $ 17,295 $ 10,618
Grant date fair value of shares that vested during the year 7,954 6,040 5,040
Share-based compensation 8,001 6,874 5,045
Tax benefit related to share-based compensation expense 2,016 $ 1,732 $ 1,791
Unrecognized compensation cost $ 8,654    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 1 year 8 months 12 days