Annual report pursuant to Section 13 and 15(d)

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

v3.10.0.1
Shareholders' Equity, Stock Options and Net Income per Share - Non-employee Director Non-vested Shares (Details) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 12 Months Ended
May 31, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Non-Vested Shares [Line Items]        
Share-based compensation   $ 10,549 $ 8,103 $ 8,334
Nonemployee Director Nonvested Shares Granted [Member]        
Non-Vested Shares [Line Items]        
Outstanding at beginning of year (shares)   11,000 16,000 15,000
Granted (shares)   16,000 14,000 16,000
Vested (shares)   (12,000) (16,000) (15,000)
Forfeited (shares)     (3,000)  
Outstanding at end of year (shares)   15,000 11,000 16,000
Weighted average grant date fair value of non-vested shares at beginning of year   $ 52 $ 44 $ 51
Weighted Average Grant Date Fair Value   59 52 44
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value   52 44 51
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value     49  
Weighted average grant date fair value non-vested shares at end of year   $ 59 $ 52 $ 44
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value   $ 920 $ 742 $ 688
Grant date fair value of shares that vested during the year   615 809 639
Share-based compensation   775 608 728
Tax benefit related to share-based compensation expense   195 $ 216 $ 263
Unrecognized compensation cost   $ 360    
Additional shares authorized available for grant 160,000      
Number of shares authorized under the plan   360,000    
Shares available for grant   132,313    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition   4 months 11 days