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Employee Benefit Plans (Details)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 31, 2019
USD ($)
Installment
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Defined Benefit Plan Disclosure [Line Items]      
Employer contribution for defined contribution plan $ 3.5 $ 3.2 $ 2.8
Employee Stock Ownership Plan, common stock, fair value $ 17.3    
Employee Stock Ownership Plan, common stock, shares outstanding (shares) | shares 131,165    
Nonqualified Deferred Compensation Plan      
Defined Benefit Plan Disclosure [Line Items]      
Deferred compensation expense $ 0.3 $ 0.3 $ 0.2
Number of annual installments of deferred compensation (installment) | Installment 2    
Number of days after departure from board of directors for payment of deferred compensation (days) 90 days    
Outside Directors      
Defined Benefit Plan Disclosure [Line Items]      
Number of deferred common stock (shares) | shares 10,738 12,240 12,293
Vested | $ / shares $ 117.73 $ 92.63 $ 101.34