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Plan Contributions (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Payment for Pension and Other Postretirement Benefits $ 12,700 $ 12,700
Other Postretirement Benefits Plan    
Defined Benefit Plan Disclosure [Line Items]    
Payment for Pension and Other Postretirement Benefits 6,058 7,033
Supplemental Employee Retirement Plan    
Defined Benefit Plan Disclosure [Line Items]    
Payment for Pension and Other Postretirement Benefits 2,674 2,344
Defined Contribution Plan, Company Retirement    
Defined Benefit Plan Disclosure [Line Items]    
Defined Contribution Plan, Employer Discretionary Contribution Amount 10,455 9,714
Defined Contribution Plan, 401K    
Defined Benefit Plan Disclosure [Line Items]    
Defined Contribution Plan, Employer Discretionary Contribution Amount $ 15,240 $ 14,558