SUPPLEMENTAL CONSOLIDATING FINANCIAL INFORMATION - Supplemental Consolidating Statements of Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ (4,087)	$ (222)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	741	729
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	1,001	643
Tax effect of other comprehensive income gains	0	(504)
Unrealized and realized gains and losses on available-for-sale securities	0	(69)
Other comprehensive income	1,742	799
Comprehensive income (loss) attributable to Westmoreland Coal Company	(2,345)	577
Parent/ Issuer
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(4,087)	(222)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	741	729
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	1,001	643
Tax effect of other comprehensive income gains		(504)
Unrealized and realized gains and losses on available-for-sale securities		(69)
Other comprehensive income	1,742	799
Comprehensive income (loss) attributable to Westmoreland Coal Company	(2,345)	577
Co-Issuer
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(1,004)	2,782
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	6	5
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	0	0
Tax effect of other comprehensive income gains		0
Unrealized and realized gains and losses on available-for-sale securities		0
Other comprehensive income	6	5
Comprehensive income (loss) attributable to Westmoreland Coal Company	(998)	2,787
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	6,876	9,454
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	0	0
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	0	0
Tax effect of other comprehensive income gains		0
Unrealized and realized gains and losses on available-for-sale securities		1
Other comprehensive income	0	1
Comprehensive income (loss) attributable to Westmoreland Coal Company	6,876	9,455
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	1,141	(1,066)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	193	186
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	213	243
Tax effect of other comprehensive income gains		0
Unrealized and realized gains and losses on available-for-sale securities		(18)
Other comprehensive income	406	411
Comprehensive income (loss) attributable to Westmoreland Coal Company	1,547	(655)
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(7,013)	(11,170)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	(199)	(191)
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	(213)	(243)
Tax effect of other comprehensive income gains		0
Unrealized and realized gains and losses on available-for-sale securities		17
Other comprehensive income	(412)	(417)
Comprehensive income (loss) attributable to Westmoreland Coal Company	$ (7,425)	$ (11,587)