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Defined Benefit Post-Retirement Plans (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Defined Benefit Post-Retirement Plans [Abstract]    
Employer contributions $ 0 $ 0
Pension Benefits [Member]    
Components of net periodic cost (benefit) [Abstract]    
Service cost 435 420
Interest cost 981 920
Expected return on plan assets (1,873) (2,123)
Net amortization 639 251
Total net periodic cost (benefit) 182 (532)
Other Benefits [Member]    
Components of net periodic cost (benefit) [Abstract]    
Service cost 2 3
Interest cost 81 82
Expected return on plan assets 0 0
Net amortization 17 44
Total net periodic cost (benefit) $ 100 $ 129