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)

v3.6.0.2
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, 2016
Dec. 31, 2015
Dec. 31, 2014
Non-Vested Shares [Line Items]        
Share-based compensation   $ 8,334 $ 7,486 $ 6,681
Nonemployee Director Nonvested Shares Granted [Member]        
Non-Vested Shares [Line Items]        
Non-vested share vesting period   1 year    
Outstanding at beginning of year (shares)   15,000 15,000 15,000
Granted (shares)   16,000 14,000 15,000
Vested (shares)   (15,000) (14,000) (15,000)
Outstanding at end of year (shares)   16,000 15,000 15,000
Weighted average grant date fair value of non-vested shares at beginning of year   $ 51 $ 44 $ 38
Weighted Average Grant Date Fair Value   44 51 44
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value   51 43 38
Weighted average grant date fair value non-vested shares at end of year   $ 44 $ 51 $ 44
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value   $ 688 $ 740 $ 650
Grant date fair value of shares that vested during the year   639 727 632
Share-based compensation   728 661 589
Tax benefit related to share-based compensation expense   263 $ 259 $ 225
Unrecognized compensation cost   $ 246    
Additional shares authorized available for grant 160,000      
Number of shares authorized under the plan   360,000    
Shares available for grant   159,259    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition   4 months 11 days