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Employee Benefit Plans (Schedule of SERP's Pension Cost) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]      
Service cost - benefits earned during the year $ 4,017 $ 3,733  
Interest cost on projected benefit obligations 3,703 3,621  
Supplemental Executive Retirement Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost - benefits earned during the year 92 143 $ 133
Interest cost on projected benefit obligations 348 360 367
Net amortization and deferral 581 324 295
Net periodic pension cost $ 1,021 $ 827 $ 795