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Benefit Plans, Other Plans (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Other Plans [Abstract]      
Employer contribution matching, first 1% of employee contribution 100.00%    
Employer contribution percent of employee contribution, 100% matching 1.00%    
Employer contribution matching, next 5% of employee contribution 50.00%    
Employer contribution percent of employee contribution, 50% matching 5.00%    
Employer matching contribution $ 4,770 $ 3,932 $ 3,884