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Postretirement Benefit Plans - Assumptions Used (Details)
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Defined Benefit Postretirement Health And Life Coverage      
Weighted Average Assumptions Used in Calculating Benefit Obligation      
Discount rate 4.67% 4.90%  
Rate of compensation increase 0.00% 0.00%  
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost      
Discount rate 4.90% 2.40% 2.25%
Rate of compensation increase 0.00% 0.00% 2.00%
Director's Retirement Plan      
Weighted Average Assumptions Used in Calculating Benefit Obligation      
Discount rate 4.80% 4.90%  
Change in consumer price index 3.40% 7.00%  
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost      
Discount rate 4.80% 4.90% 2.40%
Change in consumer price index 3.40% 7.00% 1.40%
Scottdale Defined Benefit Pension Plan      
Weighted Average Assumptions Used in Calculating Benefit Obligation      
Discount rate 5.00% 5.25%  
Expected long-term return on plan assets 4.50% 4.50%  
Rate of compensation increase 2.50% 2.50%  
Riverview Defined Benefit Plan | Union      
Weighted Average Assumptions Used in Calculating Benefit Obligation      
Discount rate 5.02% 2.83%  
Expected long-term return on plan assets 6.00% 6.00%  
Riverview Defined Benefit Plan | Citizens      
Weighted Average Assumptions Used in Calculating Benefit Obligation      
Discount rate 5.02% 2.83%  
Expected long-term return on plan assets 6.00% 6.00%  
Riverview Defined Benefit Plan | Postretirement Life Insurance Benefits Citizens      
Weighted Average Assumptions Used in Calculating Benefit Obligation      
Discount rate 4.70% 3.00%