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Retirement Plans (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Retirement Plans [Abstract]        
Service period of participants not impacted by pension plan amendment     15 years  
Age of plan participants not impacted by pension plan amendment     50 years  
Service period of participants who are age fifty not impacted by pension plan amendment     10 years  
Pension plan defined benefit plan cost increase limit percentage     4.00%  
Higman [Member]        
Retirement Plans [Abstract]        
Pension contributions     $ 479,000  
Pension Plans [Member]        
Components of net periodic benefit cost [Abstract]        
Service cost $ 1,991 $ 1,917 5,971 $ 5,753
Interest cost 3,560 3,919 10,679 11,758
Expected return on plan assets (6,566) (5,960) (19,699) (17,883)
Amortization of actuarial loss (gain) 1,412 994 3,300 1,651
Net periodic benefit cost 397 870 251 1,279
SERP [Member]        
Components of net periodic benefit cost [Abstract]        
Service cost 0 0 0 0
Interest cost 8 10 23 30
Expected return on plan assets 0 0 0 0
Amortization of actuarial loss (gain) 10 8 30 26
Net periodic benefit cost 18 18 53 56
Other Postretirement Benefits [Member]        
Components of net periodic benefit cost [Abstract]        
Service cost 0 0 0 0
Interest cost 5 6 13 17
Amortization of actuarial loss (gain) (113) (131) (338) (392)
Net periodic benefit cost $ (108) $ (125) $ (325) $ (375)