SUPPLEMENTAL CONSOLIDATING FINANCIAL INFORMATION - Supplemental Consolidating Statements of Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Condensed Financial Statements, Captions [Line Items]
Net loss	$ (49,134)	$ (1,013)	$ (131,318)	$ (2,884)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	361	872	1,078	2,617
Adjustments to accumulated actuarial losses and transition obligations, pension	(371)	0	(172)	0
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	3	1,002	13	3,004
Tax effect of other comprehensive income gains	(487)	0	(711)	0
Change in foreign currency translation adjustment	(14,642)	0	(5,364)	0
Unrealized and realized gains and losses on available-for-sale securities	1,231	(16)	1,231	(55)
Other comprehensive income	(13,905)	1,858	(3,925)	5,566
Comprehensive income (loss) attributable to Westmoreland Coal Company	(63,039)	845	(135,243)	2,682
Parent/ Issuer
Condensed Financial Statements, Captions [Line Items]
Net loss	(49,134)	(1,013)	(131,318)	(2,884)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	361	872	1,078	2,617
Adjustments to accumulated actuarial losses and transition obligations, pension	(371)		(172)
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	3	1,002	13	3,004
Tax effect of other comprehensive income gains	(487)		(711)
Change in foreign currency translation adjustment	(14,642)		(5,364)
Unrealized and realized gains and losses on available-for-sale securities	1,231	(16)	1,231	(55)
Other comprehensive income	(13,905)	1,858	(3,925)	5,566
Comprehensive income (loss) attributable to Westmoreland Coal Company	(63,039)	845	(135,243)	2,682
Co-Issuer
Condensed Financial Statements, Captions [Line Items]
Net loss	(26,515)	5,082	(34,357)	8,913
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	(1)	7	7	21
Adjustments to accumulated actuarial losses and transition obligations, pension	0		0
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	0	0	0	0
Tax effect of other comprehensive income gains	0		0
Change in foreign currency translation adjustment	0		0
Unrealized and realized gains and losses on available-for-sale securities	0	0	0	0
Other comprehensive income	(1)	7	7	21
Comprehensive income (loss) attributable to Westmoreland Coal Company	(26,516)	5,089	(34,350)	8,934
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net loss	(8,433)	11,093	(12,004)	29,265
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	127	601	366	601
Adjustments to accumulated actuarial losses and transition obligations, pension	(371)		(172)
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	(322)	433	(108)	433
Tax effect of other comprehensive income gains	0		0
Change in foreign currency translation adjustment	(13,729)		(4,451)
Unrealized and realized gains and losses on available-for-sale securities	1,007	(39)	1,007	(56)
Other comprehensive income	(13,288)	995	(3,358)	978
Comprehensive income (loss) attributable to Westmoreland Coal Company	(21,721)	12,088	(15,362)	30,243
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net loss	206	(3,607)	512	(2,561)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	15	(386)	15	47
Adjustments to accumulated actuarial losses and transition obligations, pension	0		0
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	8	(220)	14	207
Tax effect of other comprehensive income gains	0		0
Change in foreign currency translation adjustment	0		0
Unrealized and realized gains and losses on available-for-sale securities	0	23	0	1
Other comprehensive income	23	(583)	29	255
Comprehensive income (loss) attributable to Westmoreland Coal Company	229	(4,190)	541	(2,306)
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net loss	34,742	(12,568)	45,849	(35,617)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	(141)	(222)	(388)	(669)
Adjustments to accumulated actuarial losses and transition obligations, pension	371		172
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	314	(213)	94	(640)
Tax effect of other comprehensive income gains	0		0
Change in foreign currency translation adjustment	13,729		4,451
Unrealized and realized gains and losses on available-for-sale securities	(1,007)	16	(1,007)	55
Other comprehensive income	13,266	(419)	3,322	(1,254)
Comprehensive income (loss) attributable to Westmoreland Coal Company	$ 48,008	$ (12,987)	$ 49,171	$ (36,871)