ACQUISITIONS - Narrative (Details) (USD $)	3 Months Ended		0 Months Ended			1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Jan. 01, 2015	Apr. 28, 2014 mines	Dec. 31, 2014	Jan. 31, 2015
Business Acquisition [Line Items]
Cash paid	$ 35,887,000	$ 0
Buckingham Coal Company, LLC
Business Acquisition [Line Items]
Cash paid - Initial payment			34,000,000
Cash received - working capital adjustment			1,600,000
Cash paid			32,400,000
Canadian Acquisition
Business Acquisition [Line Items]
Number of mines	6			6
Voting interests acquired (percent)				50.00%
Westmoreland Resource Partners LP
Business Acquisition [Line Items]
Units of partnership interest acquired (shares)					4,512,500
Partnership interest, reverse split, conversion ratio					12
Westmoreland Resources GP, LLC
Business Acquisition [Line Items]
Cash paid					30,000,000	3,500,000
Intangible assets					31,000,000
Finite-Lived Intangible Asset, Useful Life					15 years