SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $)	3 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Fair Value of Financial Instruments
Fair value of long-term debt, including current maturities		$ 834,300,000	$ 746,500,000
Cash Management
ARLP book overdrafts		10,300,000	6,700,000
Property, Plant and Equipment
Coal reserves not subject to depletion		118,200,000	66,900,000
Mine development costs
Capitalized mine development costs		32,600,000	73,800,000
Long lived assets
Asset impairment charge related to ARLP partnership	$ 19,000,000	$ 19,031,000
Maximum
Property, Plant and Equipment
Estimated useful life		16 years
Minimum
Property, Plant and Equipment
Estimated useful life		1 year
Mining Equipment And Processing Facilities | Maximum
Property, Plant and Equipment
Estimated useful life		16 years
Mining Equipment And Processing Facilities | Minimum
Property, Plant and Equipment
Estimated useful life		1 year
Buildings, Office Equipment And Improvements | Maximum
Property, Plant and Equipment
Estimated useful life		16 years
Buildings, Office Equipment And Improvements | Minimum
Property, Plant and Equipment
Estimated useful life		2 years
Land And Mineral Rights | Maximum
Property, Plant and Equipment
Estimated useful life		16 years
Land And Mineral Rights | Minimum
Property, Plant and Equipment
Estimated useful life		2 years