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Retirement Plans And Other Postretirement Benefits (Narrative) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]      
Pension and other postretirement liabilities $ 110,585 $ 107,446  
Percentage of change in health care cost trend rate assumptions would be immaterial 1.00%    
Expected pension expense for next twelve months $ 14,000    
Term of estimated benefit payments for fixed income securities, minimum 1 year    
Term of estimated benefit payments for fixed income securities, maximum 2 years    
Defined benefit, average remaining duration of benefit payments for pension plans 11 years 6 months    
Unfunded Non-Qualified Supplemental Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligation to unfunded plan $ 2,200    
Pension Cost (Reversal of Cost) 100    
Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligation to unfunded plan 336,159 318,763 $ 287,240
Multi-employer pension plan, pension expenses 14,646 $ 9,585 $ 10,342
Credit Spread Over London Interbank Offered Rate Basis Points 11,700    
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year (17,100)    
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year $ 17,100