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Stock Plans and Stock Based Compensation - Narrative (Details)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2020
USD ($)
$ / shares
shares
Dec. 31, 2019
USD ($)
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards granted (in shares) 86,411 62,360 65,785
Stock-based compensation expense | $ $ 4,733 $ 4,235 $ 3,477
Average grant date fair value (in dollars per share) | $ / shares $ 63.44    
SARs, shares of restricted stock and restricted units and performance share awards | 2019 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Authorized number of awards (in shares) 1,275,000    
Restricted stock awards and restricted units and performance share awards | 2019 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Reduction to shares available for grant (ratio) 4.25    
Full-value share awards | 2019 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Authorized number of awards (in shares) 300,000    
Stock options and SARs      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards granted (in shares) 0    
Stock-based compensation expense | $ $ 194 $ 235 $ 304
Unrecognized compensation cost stock option awards | $ $ 191    
Weighted average period for recognition 1 year 3 months 18 days    
Awards granted during period (in shares) 0 0 0
Stock options and SARs | 2009 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award term (no more than) 10 years    
Restricted stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards granted (in shares) 69,451 49,365 65,785
Weighted average period for recognition 3 years 4 months 24 days    
Average grant date fair value (in dollars per share) | $ / shares   $ 89.21 $ 75.44
Restricted units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards granted (in shares) 10,415 8,345  
Weighted average period for recognition 4 years 6 months    
Restricted units | 2009 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 5 years    
Performance shares      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards granted (in shares) 6,545 4,650  
Restricted stock awards and restricted units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense | $ $ 4,700 $ 4,000 $ 3,200
Unrecognized compensation cost for non-option awards | $ $ 13,500    
Minimum | Stock options and SARs | 2009 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 5 years    
Minimum | Restricted stock | 2009 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 4 years    
Maximum | Stock options and SARs | 2009 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 7 years    
Maximum | Restricted stock | 2009 Equity Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 7 years