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Retirement Plans (Details) - USD ($)
 3 Months Ended
Mar. 31, 2021
Mar. 31, 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 1,927,000 $ 1,917,000
Interest cost 3,584,000 3,890,000
Expected return on plan assets (6,574,000) (6,188,000)
Amortization of actuarial loss (gain) 1,098,000 232,000
Net periodic benefit cost 35,000 (149,000)
SERP [Member]    
Components of net periodic benefit cost [Abstract]    
Service cost 0 0
Interest cost 8,000 10,000
Expected return on plan assets 0 0
Amortization of actuarial loss (gain) 10,000 9,000
Net periodic benefit cost 18,000 19,000
Other Postretirement Benefits [Member]    
Components of net periodic benefit cost [Abstract]    
Interest cost 4,000 6,000
Amortization of actuarial loss (gain) (113,000) (131,000)
Net periodic benefit cost $ (109,000) $ (125,000)