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Employee Benefit Plans Summary of Pension Plan and Postretirement Plan Net Periodic Benefit Cost (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Pension Plan [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Interest cost $ 561 $ 681
Expected return on plan assets (1,011) (982)
Net amortization and deferral 504 465
Net periodic benefit 54 164
Other Postretirement Benefits Plan [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Interest cost 8 11
Net accretion and deferral (134) (137)
Net periodic benefit $ (126) $ (126)