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Common Unit-Based Compensation Plan - LTIP Other (Details) - ARLP LTIP - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Other information        
Unit-based compensation expense $ 2.3 $ 2.3 $ 4.2 $ 4.4
Total unit-based obligation recorded 12.6   12.6  
Unrecognized compensation expense (in dollars) $ 14.5   $ 14.5  
Weighted-average period for recognition of expense     1 year 6 months