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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ (1,013)	$ 5,351	$ (2,884)	$ (8,516)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	872	729	2,617	2,187
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	1,002	643	3,004	1,929
Tax effect of other comprehensive income gains	0	(521)	0	(1,496)
Unrealized and realized gains and losses on available-for-sale securities	(16)	(25)	(55)	(248)
Other comprehensive income	1,858	826	5,566	2,372
Comprehensive income (loss) attributable to Westmoreland Coal Company	845	6,177	2,682	(6,144)
Parent/ Issuer
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(1,013)	5,351	(2,884)	(8,516)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	872	729	2,617	2,187
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	1,002	643	3,004	1,929
Tax effect of other comprehensive income gains		(521)		(1,496)
Unrealized and realized gains and losses on available-for-sale securities	(16)	(25)	(55)	(248)
Other comprehensive income	1,858	826	5,566	2,372
Comprehensive income (loss) attributable to Westmoreland Coal Company	845	6,177	2,682	(6,144)
Co-Issuer
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	5,082	4,016	8,913	5,042
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	7	6	21	16
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
Unrealized and realized gains and losses on available-for-sale securities	0	0	0	0
Other comprehensive income	7	6	21	16
Comprehensive income (loss) attributable to Westmoreland Coal Company	5,089	4,022	8,934	5,058
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	6,543	12,205	22,257	29,172
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	0	0	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
Unrealized and realized gains and losses on available-for-sale securities	0	1	(17)	1
Other comprehensive income	0	1	(17)	1
Comprehensive income (loss) attributable to Westmoreland Coal Company	6,543	12,206	22,240	29,173
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	30	1,569	2,280	(3,043)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	215	185	648	557
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	213	243	640	729
Tax effect of other comprehensive income gains		0		0
Unrealized and realized gains and losses on available-for-sale securities	(16)	(25)	(38)	(44)
Other comprehensive income	412	403	1,250	1,242
Comprehensive income (loss) attributable to Westmoreland Coal Company	442	1,972	3,530	(1,801)
Consolidating Adjustments
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(11,655)	(17,790)	(33,450)	(31,171)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	(222)	(191)	(669)	(573)
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	(213)	(243)	(640)	(729)
Tax effect of other comprehensive income gains		0		0
Unrealized and realized gains and losses on available-for-sale securities	16	24	55	43
Other comprehensive income	(419)	(410)	(1,254)	(1,259)
Comprehensive income (loss) attributable to Westmoreland Coal Company	$ (12,074)	$ (18,200)	$ (34,704)	$ (32,430)