Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity, Stock Incentive Plan and Net Income per Share - Non-employee Director Non-vested Shares (Details)

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Shareholders' Equity, Stock Incentive Plan and Net Income per Share - Non-employee Director Non-vested Shares (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Non-Vested Shares [Line Items]      
Share-based compensation $ 11,033 $ 11,715 $ 10,191
Nonemployee Director Nonvested Shares Granted [Member] | Continuing Operations      
Non-Vested Shares [Line Items]      
Outstanding at beginning of year (shares) 16 15 11
Granted (shares) 24 16 16
Vested (shares) (16) (15) (12)
Outstanding at end of year (shares) 24 16 15
Weighted average grant date fair value of non-vested shares at beginning of year $ 62.17 $ 58.50 $ 52.00
Weighted Average Grant Date Fair Value 42.88 62.17 58.58
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value 62.00 64.05 52.09
Weighted average grant date fair value non-vested shares at end of year $ 42.88 $ 62.17 $ 58.50
Grant date fair value of shares that vested during the year $ 771 $ 970 $ 615
Share-based compensation 1,026 970 775
Tax benefit related to share-based compensation expense 253 $ 244 $ 195
Unrecognized compensation cost $ 376    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 4 months 24 days    
Non-employee Director Stock Options [Member] | Continuing Operations      
Non-Vested Shares [Line Items]      
Number of shares authorized under the plan 360    
Shares available for grant 92