SUPPLEMENTAL CONSOLIDATING FINANCIAL INFORMATION - Supplemental Consolidating Statements of Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Net loss	$ (19,030)	$ (4,087)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	359	741
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	5	1,001
Tax effect of other comprehensive income gains	(138)	0
Other comprehensive income	226	1,742
Comprehensive income (loss) attributable to Westmoreland Coal Company	(18,804)	(2,345)
Parent/ Issuer
Condensed Financial Statements, Captions [Line Items]
Net loss	(19,030)	(4,087)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	359	741
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	5	1,001
Tax effect of other comprehensive income gains	(138)
Other comprehensive income	226	1,742
Comprehensive income (loss) attributable to Westmoreland Coal Company	(18,804)	(2,345)
Co-Issuer
Condensed Financial Statements, Captions [Line Items]
Net loss	1,703	(1,004)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	2	6
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
Other comprehensive income	2	6
Comprehensive income (loss) attributable to Westmoreland Coal Company	1,705	(998)
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net loss	5,803	6,876
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	(119)	0
Tax effect of other comprehensive income gains	0
Other comprehensive income	(119)	0
Comprehensive income (loss) attributable to Westmoreland Coal Company	5,684	6,876
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net loss	726	1,141
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	128	193
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	88	213
Tax effect of other comprehensive income gains	0
Other comprehensive income	216	406
Comprehensive income (loss) attributable to Westmoreland Coal Company	942	1,547
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net loss	(8,232)	(7,013)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	(130)	(199)
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	31	(213)
Tax effect of other comprehensive income gains	0
Other comprehensive income	(99)	(412)
Comprehensive income (loss) attributable to Westmoreland Coal Company	$ (8,331)	$ (7,425)