SUPPLEMENTAL CONSOLIDATING FINANCIAL INFORMATION - Supplemental Consolidating Statements of Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ (8,127)	$ (13,662)	$ (36,875)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	3,490	2,960	1,647
Adjustments to accumulated actuarial losses and transition obligations, pension	28,974	(9,812)	(15,798)
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	4,005	2,572	(288)
Adjustments to accumulated actuarial gains and transition obligations, postretirement medical benefits	53,230	(22,342)	(49,136)
Tax effect of other comprehensive income gains	(4,892)	0	0
Unrealized and realized gains and losses on available-for-sale securities	(57)	(268)	(200)
Other comprehensive loss	84,750	(26,890)	(63,775)
Comprehensive income (loss) attributable to Westmoreland Coal Company	76,623	(40,552)	(100,650)
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(8,127)	(13,662)	(36,875)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	3,490	2,960	1,647
Adjustments to accumulated actuarial losses and transition obligations, pension	28,974	(9,812)	(15,798)
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	4,005	2,572	(288)
Adjustments to accumulated actuarial gains and transition obligations, postretirement medical benefits	53,230	(22,342)	(49,136)
Tax effect of other comprehensive income gains	(4,892)
Unrealized and realized gains and losses on available-for-sale securities	(57)	(268)	(200)
Other comprehensive loss	84,750	(26,890)	(63,775)
Comprehensive income (loss) attributable to Westmoreland Coal Company	76,623	(40,552)	(100,650)
Co-Issuer [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	4,215	8,113	5,089
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	28	23	9
Adjustments to accumulated actuarial losses and transition obligations, pension	180	(52)	(150)
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	0	0	0
Adjustments to accumulated actuarial gains and transition obligations, postretirement medical benefits	0	0	0
Tax effect of other comprehensive income gains	0
Unrealized and realized gains and losses on available-for-sale securities	0	0	0
Other comprehensive loss	208	(29)	(141)
Comprehensive income (loss) attributable to Westmoreland Coal Company	4,423	8,084	4,948
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	16,079	37,771	3,463
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	0	0	0
Adjustments to accumulated actuarial losses and transition obligations, pension	10,554	(3,034)	0
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	0	0	0
Adjustments to accumulated actuarial gains and transition obligations, postretirement medical benefits	11,941	(1,969)	0
Tax effect of other comprehensive income gains	0
Unrealized and realized gains and losses on available-for-sale securities	(17)	1	(103)
Other comprehensive loss	22,478	(5,002)	(103)
Comprehensive income (loss) attributable to Westmoreland Coal Company	38,557	32,769	3,360
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	13,072	(4,541)	5,073
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	863	766	702
Adjustments to accumulated actuarial losses and transition obligations, pension	3,252	(2,132)	(444)
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	852	973	295
Adjustments to accumulated actuarial gains and transition obligations, postretirement medical benefits	5,411	(865)	(9,269)
Tax effect of other comprehensive income gains	0
Unrealized and realized gains and losses on available-for-sale securities	(38)	(65)	(100)
Other comprehensive loss	10,340	(1,323)	(8,816)
Comprehensive income (loss) attributable to Westmoreland Coal Company	23,412	(5,864)	(3,743)
Consolidating Adjustments [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(33,366)	(41,343)	(13,625)
Other comprehensive income (loss)
Amortization of accumulated actuarial gains or losses, pension	(891)	(789)	(711)
Adjustments to accumulated actuarial losses and transition obligations, pension	(13,986)	5,218	594
Amortization of accumulated actuarial gains or losses, transition obligations, and prior service costs, postretirement medical benefit	(852)	(973)	(295)
Adjustments to accumulated actuarial gains and transition obligations, postretirement medical benefits	(17,352)	2,834	9,269
Tax effect of other comprehensive income gains	0
Unrealized and realized gains and losses on available-for-sale securities	55	64	203
Other comprehensive loss	(33,026)	6,354	9,060
Comprehensive income (loss) attributable to Westmoreland Coal Company	$ (66,392)	$ (34,989)	$ (4,565)