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COMMON UNIT-BASED COMPENSATION PLANS - LTIP Grants (Details) - ARLP LTIP - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended
Mar. 31, 2025
Dec. 31, 2024
Number of units    
Balance at the beginning of the period (in units) 1,458,564  
Granted (in units) 353,028  
Vested (in units) (625,649)  
Forfeited (in units) (6,222)  
Balance at the end of the period (in units) 1,179,721  
Weighted average grant date fair value per unit    
Balance at the beginning of the period (in dollars per unit) $ 17.6  
Granted (in dollars per unit) 26.92  
Vested (in dollars per unit) 13.62  
Forfeited (in dollars per unit) 20.66  
Balance at the end of the period (in dollars per unit) $ 22.49  
Intrinsic value (in dollars)    
Intrinsic value of outstanding grants (in dollars) $ 32,183 $ 38,346
Other information    
Common units issued 366,043