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ORGANIZATION AND PRESENTATION - Exchange Transaction (Details) - shares
9 Months Ended
Jul. 28, 2017
Sep. 30, 2017
ARLP    
Ownership interests    
Units owned by parent 87,188,338 87,188,338
Intermediate Partnership    
Ownership interests    
Ownership percentage by general partners 1.0001% 1.0001%
Alliance Coal    
Ownership interests    
Ownership percentage by general partners 0.001%  
MGP II    
Ownership interests    
Ownership interest (as a percent) 100.00%  
SGP | ARLP    
Ownership interests    
Ownership percentage by general partners   0.01%
MGP II | ARLP    
Ownership interests    
Units owned by parent 56,100,000  
Exchange Transaction | SGP | ARLP    
Ownership interests    
Ownership percentage by noncontrolling owners 0.01%  
Exchange Transaction | SGP | Intermediate Partnership    
Ownership interests    
Ownership percentage by noncontrolling owners 0.01%  
Exchange Transaction | MGP | ARLP    
Ownership interests    
Common units issued in exchange 56,100,000  
Exchange Transaction | SGP | ARLP    
Ownership interests    
Common units issued in exchange 7,181