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Employee Benefit Plans (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Pension    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Interest cost $ 5,749 $ 5,958
Expected return on plan assets (5,742) (5,484)
Amortization of net actuarial loss (gain) 298 137
Net periodic benefit cost 305 611
Expected minimum required contributions 12,320  
Black Lung    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Service cost 601 513
Interest cost 1,307 1,165
Expected return on plan assets (13) (13)
Amortization of net actuarial loss (gain) 721 (708)
Net periodic benefit cost $ 2,616 $ 957