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Employee Benefit Plans (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2030
Dec. 20, 2019
Defined Benefit Plan Disclosure [Line Items]          
Defined contribution plan employer contribution percentage for branch offices, minimum 5.10%        
Defined contribution plan employer contribution percentage for branch offices, maximum 64.80%        
Company contributions $ 6,825,000 $ 4,750,000 $ 77,743,000    
Pension Plans Defined Benefit [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Estimated transition obligation amortized from accumulated other comprehensive income into net public benefit cost over the next year 0        
Estimated actuarial loss amortized from accumulated other comprehensive income into net periodic benefit cost over the next year (7,709,000)        
Estimated prior service cost amortized from accumulated other comprehensive income into net periodic benefit cost over the next year 0        
Company contributions 6,825,000 4,750,000      
Defined Benefit Postretirement Health Coverage [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Estimated transition obligation amortized from accumulated other comprehensive income into net public benefit cost over the next year 0        
Estimated actuarial loss amortized from accumulated other comprehensive income into net periodic benefit cost over the next year 46,000        
Estimated prior service cost amortized from accumulated other comprehensive income into net periodic benefit cost over the next year $ (577,000) $ (577,000) $ (577,000)    
Weighted average discount rate used to determine net periodic benefit cost 3.28% 4.27% 3.62%    
Rate of compensation increase to determine the net periodic benefit cost 4.00% 4.00% 4.00%    
Expected long-term rate of return on plan assets 7.00% 7.00% 7.00%    
Weighted average discount rates used to determine actuarial present value of the projected benefit obligation 2.55% 3.28% 4.27%   3.28%
Defined contribution plans, employer contribution plans, employer contribution percentage, maximum 3.00%        
Defined contribution plans, employer contribution percentage, for new hires, minimum 3.00%        
Defined contribution plans, employer contribution percentage, for new hires, maximum 8.00%        
Defined Contribution Plan Employer Contribution Percentage Vested After Three Years 100.00%        
Healthcare inflation rate 6.75%        
Defined Benefit Postretirement Health Coverage [Member] | Scenario Forecast [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Healthcare inflation rate       4.75%  
Defined Benefit Postretirement Health Coverage [Member] | Equity Securities [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Plan assets consist of shares in investment trusts, percentage 72.00%        
Defined Benefit Postretirement Health Coverage [Member] | Fixed Maturities [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Plan assets consist of shares in investment trusts, percentage 27.00%        
Defined Benefit Postretirement Health Coverage [Member] | Limited Partnerships [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Plan assets consist of shares in investment trusts, percentage 1.00%        
Defined Benefit Postretirement Health Coverage [Member] | Cash [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Plan assets consist of shares in investment trusts, percentage 0.00%        
Defined Benefit Postretirement Health Coverage [Member] | Equity Funds [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Target asset allocation percentage 70.00%        
Defined Benefit Postretirement Health Coverage [Member] | Bonds [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Target asset allocation percentage 30.00%        
Defined Benefit Postretirement Health Coverage [Member] | Qualified Plan [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Private equity limited partnerships $ 4,596,000 $ 20,351,000      
Company contributions