ACQUISITIONS - Peabody and CONSOL (Details) T in Millions, $ in Millions	1 Months Ended
	Dec. 31, 2014 USD ($) T	Nov. 30, 2014 USD ($) subsidiary T	Jun. 30, 2013 USD ($) T
Coal Reserves in Western Kentucky | WKY CoalPlay | Variable Interest Entity, Not Primary Beneficiary
Property, Plant and Equipment
Coal reserves conveyed by related party (in tons)	31.5
Coal Reserves in Western Kentucky | WKY CoalPlay | Variable Interest Entity, Not Primary Beneficiary | Coal lease
Property, Plant and Equipment
Coal reserves leased from related party (in tons)	22.6
Coal Reserves in Western Kentucky and Southern Indiana | WKY CoalPlay | Variable Interest Entity, Not Primary Beneficiary
Property, Plant and Equipment
Coal reserves conveyed by related party (in tons)	14.3
Coal Reserves in Western Kentucky and Southern Indiana | WKY CoalPlay | Variable Interest Entity, Not Primary Beneficiary | Coal lease
Property, Plant and Equipment
Coal reserves leased from related party (in tons)	72.3
Alliance Resource Properties | Coal Reserves in Western Kentucky | Midwest and Cyprus Creek Land Company
Property, Plant and Equipment
Coal reserves, rights purchased (in tons)	86.2
Alliance Resource Properties | Coal Reserves in Grant and Tucker Counties, West Virginia | Laurel Run Mining Company
Property, Plant and Equipment
Coal reserves, rights purchased (in tons)			11.6
Additional coal resources (in tons)			5.9
Purchase price (in dollars) | $			$ 25.2
Alliance Resource Properties | Coal Reserves and Surface Properties in Western Kentucky | CNX RCPC and Island Creek
Property, Plant and Equipment
Coal reserves, rights purchased (in tons)		124.2
Purchase price (in dollars) | $		$ 11.6
Reclamation liabilities assumed (in dollars) | $		$ 6.0
WKY CoalPlay | Coal Reserves in Western Kentucky | Midwest
Property, Plant and Equipment
Coal reserves, rights purchased (in tons)	54.1
Purchase price (in dollars) | $	$ 29.6
WKY CoalPlay | Coal Reserves in Western Kentucky and Southern Indiana | CNX RCPC and Island Creek
Property, Plant and Equipment
Coal reserves, rights purchased (in tons)		86.6
Purchase price (in dollars) | $		$ 57.2
Number of subsidiaries purchased in coal reserves acquisition | subsidiary		2