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Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Pension    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Interest cost $ 5,805 $ 5,749
Expected return on plan assets (4,920) (5,742)
Amortization of net actuarial loss 378 298
Net periodic benefit cost 1,263 305
Black Lung    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Service cost 535 601
Interest cost 1,463 1,307
Expected return on plan assets (13) (13)
Amortization of net actuarial loss 1,076 721
Net periodic benefit cost $ 3,061 $ 2,616