SUPPLEMENTAL CONSOLIDATING FINANCIAL INFORMATION - Supplemental Consolidating Statements of Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ (63,154)	$ 2,217	$ (82,185)	$ (1,870)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	359	1,004	717	1,745
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	5	1,001	10	2,002
Tax effect of other comprehensive income gains	64	0	(224)	0
Change in foreign currency translation adjustment	9,477	0	9,477	0
Unrealized and realized gains and losses on available-for-sale securities	0	(39)	0	(39)
Other comprehensive income	9,905	1,966	9,980	3,708
Comprehensive income (loss) attributable to Westmoreland Coal Company	(53,249)	4,183	(72,205)	1,838
Parent/ Issuer
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(63,154)	2,217	(82,185)	(1,870)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	359	1,004	717	1,745
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	5	1,001	10	2,002
Tax effect of other comprehensive income gains	64		(224)
Change in foreign currency translation adjustment	9,477		9,477
Unrealized and realized gains and losses on available-for-sale securities		(39)		(39)
Other comprehensive income	9,905	1,966	9,980	3,708
Comprehensive income (loss) attributable to Westmoreland Coal Company	(53,249)	4,183	(72,205)	1,838
Co-Issuer
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(9,544)	4,833	(7,842)	3,829
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	2	8	4	14
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
Other comprehensive income	2	8	4	14
Comprehensive income (loss) attributable to Westmoreland Coal Company	(9,542)	4,841	(7,838)	3,843
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(17,131)	8,047	(9,722)	18,173
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	122	239	244	432
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	(36)	214	(72)	427
Tax effect of other comprehensive income gains	0		0
Change in foreign currency translation adjustment	9,477		9,477
Unrealized and realized gains and losses on available-for-sale securities		(40)		(40)
Other comprehensive income	9,563	413	9,649	819
Comprehensive income (loss) attributable to Westmoreland Coal Company	(7,568)	8,460	(73)	18,992
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	171	2,657	296	1,045
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	6	0	11	0
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	5	0	10	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
Other comprehensive income	11	0	21	0
Comprehensive income (loss) attributable to Westmoreland Coal Company	182	2,657	317	1,045
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	26,504	(15,537)	17,268	(23,047)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	(130)	(247)	(259)	(446)
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	31	(214)	62	(427)
Tax effect of other comprehensive income gains	0		0
Change in foreign currency translation adjustment	(9,477)		(9,477)
Unrealized and realized gains and losses on available-for-sale securities		40		40
Other comprehensive income	(9,576)	(421)	(9,674)	(833)
Comprehensive income (loss) attributable to Westmoreland Coal Company	$ 16,928	$ (15,958)	$ 7,594	$ (23,880)