ACQUISITIONS - Summary of purchase consideration and allocation of purchase consideration (Details) (USD $)	0 Months Ended	3 Months Ended								12 Months Ended				0 Months Ended		6 Months Ended	1 Months Ended	12 Months Ended
	Apr. 28, 2014	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Jun. 25, 2014	Dec. 31, 2014	Jan. 31, 2015	Dec. 31, 2015	Apr. 30, 2015
Business Acquisition [Line Items]
Net cash received in the acquisition	$ 8,100,000
Repayment of assumed liability	18,100,000
Revenues										1,115,992,000		674,686,000	600,437,000
Operating Income (Loss)		8,044,000	(29,432,000)	(29,640,000)	8,053,000	(883,000)	8,536,000	11,975,000	5,734,000	(42,975,000)		25,362,000	28,872,000
Allocation of purchase consideration:
Cash and cash equivalents	26,200,000
Intangible assets			37,000,000
Indemnification asset	27,900,000
Westmoreland Resource Partners LP [Member]
Business Acquisition [Line Items]
Ownership percentage in partnership (percent)														79.00%
Partnership interest, reverse split, conversion ratio														12
Purchase consideration:
Units of partnership interest acquired (shares)		4,512,500								4,512,500				4,512,500		4,512,500
Westmoreland Resources GP, LLC [Member]
Business Acquisition [Line Items]
Ownership percentage in partnership (percent)														100.00%
LP units, closing price (in USD per share)		$ 1.00								$ 1.00				1.00		$ 1.00
Useful life of intangible assets														15 years
Purchase consideration:
Cash consideration														30,000,000
Contingent consideration		3,500,000								3,500,000				3,500,000		3,500,000
Fair value of outstanding WMLP units		10,800,000								10,800,000				10,800,000		10,800,000
Total purchase consideration														44,300,000
Allocation of purchase consideration:
Trade receivables		22,500,000								22,500,000				22,500,000		22,500,000
Inventories - materials and supplies		7,400,000								7,400,000				7,400,000		7,400,000
Inventories - coal		6,600,000								6,600,000				6,600,000		6,600,000
Other current assets		1,300,000								1,300,000				1,300,000		1,300,000
Total current assets		37,800,000								37,800,000				37,800,000		37,800,000
Land and mineral rights		38,600,000								38,600,000				38,600,000		38,600,000
Plant and equipment		134,000,000								134,000,000				134,000,000		134,000,000
Advanced coal royalties		9,200,000								9,200,000				9,200,000		9,200,000
Restricted investments and bond collateral		10,600,000								10,600,000				10,600,000		10,600,000
Intangible assets		31,000,000								31,000,000				31,000,000		31,000,000
Other assets		200,000								200,000				200,000		200,000
Total assets		261,400,000								261,400,000				261,400,000		261,400,000
Trade payables and other accrued liabilities		(19,100,000)								(19,100,000)				(19,100,000)		(19,100,000)
Asset retirement obligations		(7,800,000)								(7,800,000)				(7,800,000)		(7,800,000)
Other current liabilities		(4,000,000)								(4,000,000)				(4,000,000)		(4,000,000)
Total current liabilities		(30,900,000)								(30,900,000)				(30,900,000)		(30,900,000)
Long-term debt, less current installments		(160,100,000)								(160,100,000)				(160,100,000)		(160,100,000)
Asset retirement obligations, less current portion		(23,900,000)								(23,900,000)				(23,900,000)		(23,900,000)
Warrants		(2,000,000)								(2,000,000)				(2,000,000)		(2,000,000)
Other liabilities		(200,000)								(200,000)				(200,000)		(200,000)
Total Liabilities		(217,100,000)								(217,100,000)				(217,100,000)		(217,100,000)
Net fair value		44,300,000								44,300,000				44,300,000		44,300,000
Non-controlling Interest		(10,800,000)								(10,800,000)				(10,800,000)		(10,800,000)
Invested Equity		33,500,000								33,500,000				33,500,000		33,500,000
Sherritt International Corporation [Member]
Business Acquisition [Line Items]
Acquisition-related costs										33,600,000
Number of mines	6									6
Interest acquired (percent)	50.00%
Purchase consideration:
Cash paid - Initial payment	282,800,000													282,800,000
Cash paid - Working capital adjustment														39,800,000	39,800,000
Cash consideration	282,800,000			322,600,000										322,600,000	39,800,000
Allocation of purchase consideration:
Cash and cash equivalents		26,200,000		26,200,000						26,200,000				26,200,000		26,200,000
Trade receivables		78,100,000		49,900,000						78,100,000				78,100,000		78,100,000
Inventories - materials and supplies		52,000,000		52,000,000						52,000,000				52,000,000		52,000,000
Inventories - coal		79,800,000		79,800,000						79,800,000				79,800,000		79,800,000
Loan and lease receivables		11,200,000		11,200,000						11,200,000				11,200,000		11,200,000
Deferred tax assets		8,200,000		6,700,000						8,200,000				8,200,000		8,200,000
Other current assets		3,400,000		3,400,000						3,400,000				3,400,000		3,400,000
Total current assets		258,900,000		229,200,000						258,900,000				258,900,000		258,900,000
Land and mineral rights		202,600,000		151,300,000						202,600,000				202,600,000		202,600,000
Plant and equipment		114,800,000		139,600,000						114,800,000				114,800,000		114,800,000
Loan and lease receivables		79,100,000		83,800,000						79,100,000				79,100,000		79,100,000
Contractual third-party reclamation receivables, less current portion		6,800,000		6,800,000						6,800,000				6,800,000		6,800,000
Investment in joint venture		36,000,000		32,100,000						36,000,000				36,000,000		36,000,000
Intangible assets		37,000,000	37,000,000							37,000,000				37,000,000		37,000,000
Other assets		8,700,000		10,300,000						8,700,000				8,700,000		8,700,000
Total assets		743,900,000		653,100,000						743,900,000				743,900,000		743,900,000
Current installments of long-term debt		(36,300,000)		(36,300,000)						(36,300,000)				(36,300,000)		(36,300,000)
Trade payables and other accrued liabilities		(136,100,000)		(93,700,000)						(136,100,000)				(136,100,000)		(136,100,000)
Asset retirement obligations		(7,800,000)		(9,700,000)						(7,800,000)				(7,800,000)		(7,800,000)
Total current liabilities		(180,200,000)		(139,700,000)						(180,200,000)				(180,200,000)		(180,200,000)
Long-term debt, less current installments		(86,300,000)		(86,300,000)						(86,300,000)				(86,300,000)		(86,300,000)
Asset retirement obligations, less current portion		(122,900,000)		(92,400,000)						(122,900,000)				(122,900,000)		(122,900,000)
Deferred tax liabilities		(31,900,000)		(12,100,000)						(31,900,000)				(31,900,000)		(31,900,000)
Total Liabilities	(421,300,000)	(421,300,000)		(330,500,000)						(421,300,000)				(421,300,000)		(421,300,000)
Net fair value		322,600,000		322,600,000						322,600,000				322,600,000		322,600,000
Trade receivables. adjustments																28,200,000
Deferred tax assets, adjustments																1,500,000
Total current assets, adjustments																29,700,000
Land and mineral rights, adjustments																51,300,000
Plant and equipment, adjustments																(24,800,000)
Loan and lease receivables, adjustments																(4,700,000)
Investment in joint venture, adjustments																3,900,000
Intangible assets, adjustments																37,000,000
Other assets, adjustments																(1,600,000)
Total Assets. adjustments																90,800,000
Trade payables and other accrued liabilities, adjustments																(42,400,000)
Asset retirement obligations, adjustments																1,900,000
Total current liabilities, adjustments																(40,500,000)
Asset retirement obligations, less current portion, adjustments																(30,500,000)
Deferred tax liabilities, adjustments																(19,800,000)
Total Liabilities, adjustments																(90,800,000)
Cost of Sales [Member] | Sherritt International Corporation [Member]
Business Acquisition [Line Items]
Acquisition-related costs										14,200,000
Selling and Administrative Expenses [Member] | Westmoreland Resources GP, LLC [Member]
Business Acquisition [Line Items]
Acquisition-related costs										4,500,000
Selling and Administrative Expenses [Member] | Sherritt International Corporation [Member]
Business Acquisition [Line Items]
Acquisition-related costs										8,300,000
Foreign Currency Gain (Loss) [Member] | Sherritt International Corporation [Member]
Business Acquisition [Line Items]
Acquisition-related costs										6,200,000
Interest Expense [Member] | Sherritt International Corporation [Member]
Business Acquisition [Line Items]
Acquisition-related costs										4,900,000
Coal Canada Segment [Member]
Business Acquisition [Line Items]
Revenues										388,664,000	[1]
Operating Income (Loss)										(2,670,000)	[1]
Subsequent Event [Member] | Westmoreland Resources GP, LLC [Member]
Purchase consideration:
Cash consideration																	3,500,000
WMLP [Member] | Scenario, Forecast [Member]
Allocation of purchase consideration:
Distribution per unit to partners (in USD per share)																			$ 0.20
Total distributions to partners																		$ 4,600,000
Distribution receivable by Parent (percent)																		79.00%

[1] The Canadian operations were acquired on April 28, 2014, therefore, information for the year ended December 31, 2014 includes approximately eight months of operations and there is no activity for 2013 and 2012.