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Pension and Supplemental Executive Retirement Plans - Narrative (Details)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
installment
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
installment
Sep. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
May 31, 2014
Defined Benefit Plan Disclosure [Line Items]            
Discount rate used to re-measure pension obligation           4.46%
Service cost $ 0 $ 0 $ 0 $ 0    
Supplemental Employee Retirement Plan            
Defined Benefit Plan Disclosure [Line Items]            
Discount rate used to re-measure pension obligation 4.00%   4.00%      
Benefit obligation $ 1,800   $ 1,800      
Number of equal consecutive installments | installment 180   180      
Consecutive installments, amount $ 10   $ 10      
Accrued liability 283   283   $ 1  
Service cost $ 94   $ 282