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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 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Pension Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost $ 561 $ 681 $ 1,683 $ 2,043
Expected return on plan assets (1,011) (982) (3,033) (2,946)
Net amortization and deferral 504 465 1,513 1,395
Net periodic benefit 54 164 163 492
Other Postretirement Benefits Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost 8 11 24 33
Net accretion and deferral (134) (137) (402) (411)
Net periodic benefit $ (126) $ (126) $ (378) $ (378)