SUPPLEMENTAL CONSOLIDATING FINANCIAL INFORMATION - Supplemental Consolidating Balance Sheet Information (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current assets:
Cash and cash equivalents	$ 31,610	$ 30,783	$ 5,775	$ 10,519
Receivables:
Trade	60,037	46,235
Contractual third-party reclamation receivables	10,207	11,259
Intercompany receivable/payable	0	0
Other	3,220	3,493
Total receivables	73,464	60,987
Inventories	37,734	25,696
Other current assets	16,504	4,987
Total current assets	159,312	122,453
Property, plant and equipment:
Land and mineral rights	261,741	198,201
Plant and equipment	635,720	527,127
Gross property, plant and equipment	897,461	725,328
Less accumulated depreciation, depletion and amortization	(384,621)	(328,596)
Net property, plant and equipment	512,840	396,732
Advanced coal royalties	4,316	2,552
Reclamation Deposits	72,718	71,939
Restricted investments and bond collateral	87,209	58,305
Contractual third-party reclamation receivables, less current portion	84,158	87,674
Intangible assets	3,203	4,879
Investment in subsidiaries	0	0
Other assets	12,359	14,638
Total Assets	936,115	759,172	750,306
Current liabilities
Current installments of long-term debt	23,791	20,795
Accounts payable and accrued expenses:
Trade	52,093	45,326
Production taxes	33,228	25,605
Workers' compensation	820	911
Postretirement medical benefits	14,068	13,179
SERP	390	391
Deferred revenue	12,822	9,852
Asset retirement obligations	22,238	19,765
Other current liabilities	11,462	8,298
Total current liabilities	170,912	144,122
Long-term debt, less current installments	337,198	261,474
Workers' compensation, less current portion	8,710	10,715
Excess of pneumoconiosis benefit obligation over trust assets	8,356	6,565
Postretirement medical benefits, less current portion	319,775	245,462
Pension and SERP obligations, less current portion	54,250	28,991
Deferred revenue, less current portion	56,891	65,834
Asset retirement obligations, less current portion	241,609	227,713
Intangible liabilities	6,625	7,644
Other liabilities	18,020	10,510
Intercompany receivable/payable	0	0
Total liabilities	1,222,346	1,009,030
Shareholders' deficit:
Preferred stock	160	160
Common stock	35,502	34,527
Other paid-in capital	130,852	126,288
Accumulated other comprehensive loss	(148,345)	(121,455)	(57,680)	(31,223)
Accumulated earnings (deficit)	(289,727)	(281,141)
Total Westmoreland Coal Company shareholders' deficit	(271,558)	(241,621)
Noncontrolling interest	(14,673)	(8,237)
Total equity (deficit)	(286,231)	(249,858)	(162,355)	(141,799)
Total Liabilities and Shareholders' Deficit	936,115	759,172
Parent Company [Member]
Current assets:
Cash and cash equivalents	14,836	26,141	271	755
Receivables:
Trade	0	0
Contractual third-party reclamation receivables	0	0
Intercompany receivable/payable	(8,002)	(20,756)
Other	77	224
Total receivables	(7,925)	(20,532)
Inventories	0	0
Other current assets	739	668
Total current assets	7,650	6,277
Property, plant and equipment:
Land and mineral rights	0	0
Plant and equipment	3,198	3,249
Gross property, plant and equipment	3,198	3,249
Less accumulated depreciation, depletion and amortization	(2,364)	(2,140)
Net property, plant and equipment	834	1,109
Advanced coal royalties	0	0
Reclamation Deposits	0	0
Restricted investments and bond collateral	15,183	13,532
Contractual third-party reclamation receivables, less current portion	0	0
Intangible assets	0	0
Investment in subsidiaries	248,565	161,371
Other assets	10,267	11,085
Total Assets	282,499	193,374
Current liabilities
Current installments of long-term debt	(1,548)	1,125
Accounts payable and accrued expenses:
Trade	4,707	4,286
Production taxes	0	0
Workers' compensation	820	911
Postretirement medical benefits	12,494	11,796
SERP	390	391
Deferred revenue	0	0
Asset retirement obligations	0	0
Other current liabilities	11,312	6,752
Total current liabilities	28,175	25,261
Long-term debt, less current installments	245,456	143,991
Workers' compensation, less current portion	8,710	10,715
Excess of pneumoconiosis benefit obligation over trust assets	8,356	6,565
Postretirement medical benefits, less current portion	224,336	207,650
Pension and SERP obligations, less current portion	29,265	25,555
Deferred revenue, less current portion	0	0
Asset retirement obligations, less current portion	0	0
Intangible liabilities	0	0
Other liabilities	701	976
Intercompany receivable/payable	23,731	22,519
Total liabilities	568,730	443,232
Shareholders' deficit:
Preferred stock	160	160
Common stock	35,502	34,527
Other paid-in capital	130,852	126,288
Accumulated other comprehensive loss	(148,345)	(121,455)
Accumulated earnings (deficit)	(289,727)	(281,141)
Total Westmoreland Coal Company shareholders' deficit	(271,558)	(241,621)
Noncontrolling interest	(14,673)	(8,237)
Total equity (deficit)	(286,231)	(249,858)
Total Liabilities and Shareholders' Deficit	282,499	193,374
Co-Issuer [Member]
Current assets:
Cash and cash equivalents	4,545	6	880	138
Receivables:
Trade	13,018	12,651
Contractual third-party reclamation receivables	0	0
Intercompany receivable/payable	0	0
Other	0	216
Total receivables	13,018	12,867
Inventories	3,047	3,756
Other current assets	298	179
Total current assets	20,908	16,808
Property, plant and equipment:
Land and mineral rights	1,395	1,395
Plant and equipment	219,857	217,846
Gross property, plant and equipment	221,252	219,241
Less accumulated depreciation, depletion and amortization	(61,474)	(51,864)
Net property, plant and equipment	159,778	167,377
Advanced coal royalties	0	0
Reclamation Deposits	0	0
Restricted investments and bond collateral	5,990	5,983
Contractual third-party reclamation receivables, less current portion	0	0
Intangible assets	2,923	4,563
Investment in subsidiaries	0	0
Other assets	0	0
Total Assets	189,599	194,731
Current liabilities
Current installments of long-term debt	0	0
Accounts payable and accrued expenses:
Trade	4,978	8,183
Production taxes	3	3
Workers' compensation	0	0
Postretirement medical benefits	0	0
SERP	0	0
Deferred revenue	8,788	8,800
Asset retirement obligations	0	0
Other current liabilities	0	259
Total current liabilities	13,769	17,245
Long-term debt, less current installments	0	0
Workers' compensation, less current portion	0	0
Excess of pneumoconiosis benefit obligation over trust assets	0	0
Postretirement medical benefits, less current portion	0	0
Pension and SERP obligations, less current portion	289	245
Deferred revenue, less current portion	50,239	58,539
Asset retirement obligations, less current portion	829	770
Intangible liabilities	6,625	7,644
Other liabilities	0	0
Intercompany receivable/payable	0	0
Total liabilities	71,751	84,443
Shareholders' deficit:
Preferred stock	0	0
Common stock	5	5
Other paid-in capital	52,807	52,775
Accumulated other comprehensive loss	(372)	(343)
Accumulated earnings (deficit)	65,408	57,851
Total Westmoreland Coal Company shareholders' deficit	117,848	110,288
Noncontrolling interest	0	0
Total equity (deficit)	117,848	110,288
Total Liabilities and Shareholders' Deficit	189,599	194,731
Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	5,362	143	0	0
Receivables:
Trade	13,428	68
Contractual third-party reclamation receivables	56	56
Intercompany receivable/payable	5,667	9,657
Other	16,806	9,256
Total receivables	35,957	19,037
Inventories	16,538	4,490
Other current assets	5,550	1,000
Total current assets	63,407	24,670
Property, plant and equipment:
Land and mineral rights	91,741	29,394
Plant and equipment	215,751	117,836
Gross property, plant and equipment	307,492	147,230
Less accumulated depreciation, depletion and amortization	(108,151)	(88,762)
Net property, plant and equipment	199,341	58,468
Advanced coal royalties	500	0
Reclamation Deposits	0	0
Restricted investments and bond collateral	39,208	13,592
Contractual third-party reclamation receivables, less current portion	327	169
Intangible assets	0	0
Investment in subsidiaries	(792)	(792)
Other assets	635	1,078
Total Assets	302,626	97,185
Current liabilities
Current installments of long-term debt	1,939	2,409
Accounts payable and accrued expenses:
Trade	15,163	4,069
Production taxes	10,014	980
Workers' compensation	0	0
Postretirement medical benefits	87	0
SERP	0	0
Deferred revenue	2,997	0
Asset retirement obligations	3,519	1,384
Other current liabilities	10	1,276
Total current liabilities	33,729	10,118
Long-term debt, less current installments	2,473	3,152
Workers' compensation, less current portion	0	0
Excess of pneumoconiosis benefit obligation over trust assets	0	0
Postretirement medical benefits, less current portion	55,981	0
Pension and SERP obligations, less current portion	19,346	0
Deferred revenue, less current portion	0	0
Asset retirement obligations, less current portion	40,063	23,373
Intangible liabilities	0	0
Other liabilities	15,677	7,901
Intercompany receivable/payable	(7,972)	(10)
Total liabilities	159,297	44,534
Shareholders' deficit:
Preferred stock	0	0
Common stock	110	110
Other paid-in capital	93,456	16,373
Accumulated other comprehensive loss	(4,987)	15
Accumulated earnings (deficit)	54,750	36,153
Total Westmoreland Coal Company shareholders' deficit	143,329	52,651
Noncontrolling interest	0	0
Total equity (deficit)	143,329	52,651
Total Liabilities and Shareholders' Deficit	302,626	97,185
Non-Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	6,867	4,493	4,624	9,626
Receivables:
Trade	33,591	33,516
Contractual third-party reclamation receivables	10,151	11,203
Intercompany receivable/payable	(30,641)	(22,308)
Other	1,182	2,212
Total receivables	14,283	24,623
Inventories	18,149	17,450
Other current assets	9,917	3,140
Total current assets	49,216	49,706
Property, plant and equipment:
Land and mineral rights	168,605	167,412
Plant and equipment	196,914	188,196
Gross property, plant and equipment	365,519	355,608
Less accumulated depreciation, depletion and amortization	(212,632)	(185,830)
Net property, plant and equipment	152,887	169,778
Advanced coal royalties	3,816	2,552
Reclamation Deposits	72,718	71,939
Restricted investments and bond collateral	26,828	25,198
Contractual third-party reclamation receivables, less current portion	83,831	87,505
Intangible assets	280	316
Investment in subsidiaries	3,770	3,770
Other assets	3,457	2,475
Total Assets	396,803	413,239
Current liabilities
Current installments of long-term debt	23,400	19,208
Accounts payable and accrued expenses:
Trade	42,085	35,377
Production taxes	23,211	24,622
Workers' compensation	0	0
Postretirement medical benefits	1,487	1,383
SERP	0	0
Deferred revenue	1,037	1,052
Asset retirement obligations	18,719	18,381
Other current liabilities	144	44
Total current liabilities	110,083	100,067
Long-term debt, less current installments	91,269	114,331
Workers' compensation, less current portion	0	0
Excess of pneumoconiosis benefit obligation over trust assets	0	0
Postretirement medical benefits, less current portion	39,458	37,812
Pension and SERP obligations, less current portion	5,350	3,191
Deferred revenue, less current portion	6,652	7,295
Asset retirement obligations, less current portion	200,717	203,570
Intangible liabilities	0	0
Other liabilities	1,642	1,633
Intercompany receivable/payable	35,787	29,202
Total liabilities	490,958	497,101
Shareholders' deficit:
Preferred stock	0	0
Common stock	132	132
Other paid-in capital	62,539	59,893
Accumulated other comprehensive loss	(24,492)	(23,168)
Accumulated earnings (deficit)	(132,334)	(120,719)
Total Westmoreland Coal Company shareholders' deficit	(94,155)	(83,862)
Noncontrolling interest	0	0
Total equity (deficit)	(94,155)	(83,862)
Total Liabilities and Shareholders' Deficit	396,803	413,239
Consolidating Adjustments [Member]
Current assets:
Cash and cash equivalents	0	0	0	0
Receivables:
Trade	0	0
Contractual third-party reclamation receivables	0	0
Intercompany receivable/payable	32,976	33,407
Other	(14,845)	(8,415)
Total receivables	18,131	24,992
Inventories	0	0
Other current assets	0	0
Total current assets	18,131	24,992
Property, plant and equipment:
Land and mineral rights	0	0
Plant and equipment	0	0
Gross property, plant and equipment	0	0
Less accumulated depreciation, depletion and amortization	0	0
Net property, plant and equipment	0	0
Advanced coal royalties	0	0
Reclamation Deposits	0	0
Restricted investments and bond collateral	0	0
Contractual third-party reclamation receivables, less current portion	0	0
Intangible assets	0	0
Investment in subsidiaries	(251,543)	(164,349)
Other assets	(2,000)	0
Total Assets	(235,412)	(139,357)
Current liabilities
Current installments of long-term debt	0	(1,947)
Accounts payable and accrued expenses:
Trade	(14,840)	(6,589)
Production taxes	0	0
Workers' compensation	0	0
Postretirement medical benefits	0	0
SERP	0	0
Deferred revenue	0	0
Asset retirement obligations	0	0
Other current liabilities	(4)	(33)
Total current liabilities	(14,844)	(8,569)
Long-term debt, less current installments	(2,000)	0
Workers' compensation, less current portion	0	0
Excess of pneumoconiosis benefit obligation over trust assets	0	0
Postretirement medical benefits, less current portion	0	0
Pension and SERP obligations, less current portion	0	0
Deferred revenue, less current portion	0	0
Asset retirement obligations, less current portion	0	0
Intangible liabilities	0	0
Other liabilities	0	0
Intercompany receivable/payable	(51,546)	(51,711)
Total liabilities	(68,390)	(60,280)
Shareholders' deficit:
Preferred stock	0	0
Common stock	(247)	(247)
Other paid-in capital	(208,802)	(129,041)
Accumulated other comprehensive loss	29,851	23,496
Accumulated earnings (deficit)	12,176	26,715
Total Westmoreland Coal Company shareholders' deficit	(167,022)	(79,077)
Noncontrolling interest	0	0
Total equity (deficit)	(167,022)	(79,077)
Total Liabilities and Shareholders' Deficit	$ (235,412)	$ (139,357)