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Defined Benefit Post-Retirement Plans (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Employee Benefit Plans [Abstract]    
Employer contributions $ 0 $ 0
Pension Benefits [Member]    
Components of net periodic (benefit) cost [Abstract]    
Service cost 485 446
Interest cost 677 809
Expected return on plan assets (2,203) (2,105)
Net amortization 313 368
Net periodic pension (benefit) cost (728) (482)
Other Benefits [Member]    
Components of net periodic (benefit) cost [Abstract]    
Service cost 2 2
Interest cost 45 55
Expected return on plan assets 0 0
Net amortization 13 13
Net periodic pension (benefit) cost $ 60 $ 70