SUPPLEMENTAL CONSOLIDATING FINANCIAL INFORMATION - Supplemental Consolidating Balance Sheet Information (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 61,900	$ 61,110	$ 40,852	$ 31,610
Receivables:
Trade	64,715	66,196
Contractual third-party reclamation receivables	8,213	8,487
Intercompany receivable/payable	0	0
Other	1,375	5,086
Total receivables	74,303	79,769
Inventories	35,447	39,972
Deferred income taxes		0
Restricted investments and bond collateral	16,900	5,998
Other current assets	16,643	18,190
Total current assets	205,193	205,039
Property, plant and equipment:
Land and mineral rights	278,198	278,188
Plant and equipment	673,189	657,696
Gross property, plant and equipment	951,387	935,884
Less accumulated depreciation, depletion and amortization	461,754	445,848
Net property, plant and equipment	489,633	490,036
Advanced coal royalties	7,263	7,311
Reclamation deposits	75,315	74,921
Total restricted investments and bond collateral, less current portion	523,483	69,235
Contractual third-party reclamation receivables	88,036	88,303
Intangible assets	1,099	1,520
Investment in subsidiaries	0	0
Other assets	17,125	10,320
Total Assets	1,407,147	946,685	943,015
Current liabilities
Current installments of long-term debt	48,586	44,343
Accounts payable and accrued expenses:
Trade	62,598	57,507
Production taxes	46,794	41,905
Workers' compensation	712	717
Postretirement medical benefits	13,955	13,955
SERP	390	390
Deferred revenue	16,034	14,068
Asset retirement obligations	22,227	23,353	23,154
Other current liabilities	24,390	16,790
Total current liabilities	235,686	213,028
Long-term debt, less current installments	751,645	295,494
Workers' compensation, less current portion	6,680	6,744
Excess of black lung benefit obligation over trust assets	9,376	8,675
Postretirement medical benefits, less current portion	271,275	270,374
Pension and SERP obligations, less current portion	23,524	24,176
Deferred revenue, less current portion	43,299	46,567
Asset retirement obligations, less current portion	259,036	256,511	240,335
Intangible liabilities	5,339	5,606
Other liabilities	7,503	7,389
Intercompany receivable/payable	0	0
Total liabilities	1,613,363	1,134,564
Shareholders' deficit:
Preferred stock	121	160
Common stock	37,155	36,479
Other paid-in capital	134,952	134,861
Accumulated other comprehensive loss	(63,369)	(63,595)
Accumulated earnings (deficit)	(315,075)	(295,784)
Total equity (deficit)	(206,216)	(187,879)
Total Liabilities and Shareholders' Deficit	1,407,147	946,685
Parent/ Issuer
Current assets:
Cash and cash equivalents	28,759	25,326	(9,637)	14,836
Receivables:
Trade	0	0
Contractual third-party reclamation receivables	0	0
Intercompany receivable/payable	(2,263)	(3,568)
Other	273	95
Total receivables	(1,990)	(3,473)
Inventories	0	0
Deferred income taxes		0
Restricted investments and bond collateral	16,900	0
Other current assets	7,044	6,115
Total current assets	50,713	27,968
Property, plant and equipment:
Land and mineral rights	0	0
Plant and equipment	3,966	3,939
Gross property, plant and equipment	3,966	3,939
Less accumulated depreciation, depletion and amortization	2,781	2,705
Net property, plant and equipment	1,185	1,234
Advanced coal royalties	0	0
Reclamation deposits	0	0
Total restricted investments and bond collateral, less current portion	469,385	15,134
Contractual third-party reclamation receivables	0	0
Intangible assets	0	0
Investment in subsidiaries	237,926	266,847
Other assets	15,563	8,636
Total Assets	774,772	319,819
Current liabilities
Current installments of long-term debt	22,785	20,392
Accounts payable and accrued expenses:
Trade	9,000	4,122
Production taxes	0	0
Workers' compensation	712	717
Postretirement medical benefits	12,042	12,042
SERP	390	390
Deferred revenue	0	0
Asset retirement obligations	0	0
Other current liabilities	19,196	11,302
Total current liabilities	64,125	48,965
Long-term debt, less current installments	677,385	224,582
Workers' compensation, less current portion	6,680	6,744
Excess of black lung benefit obligation over trust assets	9,376	8,675
Postretirement medical benefits, less current portion	185,447	185,858
Pension and SERP obligations, less current portion	12,921	13,069
Deferred revenue, less current portion	0	0
Asset retirement obligations, less current portion	0	0
Intangible liabilities	0	0
Other liabilities	6,440	5,939
Intercompany receivable/payable	18,613	13,866
Total liabilities	980,987	507,698
Shareholders' deficit:
Preferred stock	121	160
Common stock	37,155	36,479
Other paid-in capital	134,953	134,861
Accumulated other comprehensive loss	(63,369)	(63,595)
Accumulated earnings (deficit)	(315,075)	(295,784)
Total equity (deficit)	(206,215)	(187,879)
Total Liabilities and Shareholders' Deficit	774,772	319,819
Co-Issuer
Current assets:
Cash and cash equivalents	4,043	3,341	4,807	4,545
Receivables:
Trade	12,456	12,934
Contractual third-party reclamation receivables	0	0
Intercompany receivable/payable	0	0
Other	208	210
Total receivables	12,664	13,144
Inventories	1,845	6,161
Deferred income taxes		0
Restricted investments and bond collateral	0	5,998
Other current assets	425	143
Total current assets	18,977	28,787
Property, plant and equipment:
Land and mineral rights	1,395	1,395
Plant and equipment	220,932	220,872
Gross property, plant and equipment	222,327	222,267
Less accumulated depreciation, depletion and amortization	74,177	71,653
Net property, plant and equipment	148,150	150,614
Advanced coal royalties	0	0
Reclamation deposits	0	0
Total restricted investments and bond collateral, less current portion	0	0
Contractual third-party reclamation receivables	0	0
Intangible assets	871	1,283
Investment in subsidiaries	0	0
Other assets	0	0
Total Assets	167,998	180,684
Current liabilities
Current installments of long-term debt	0	0
Accounts payable and accrued expenses:
Trade	6,331	10,119
Production taxes	405	3
Workers' compensation	0	0
Postretirement medical benefits	0	0
SERP	0	0
Deferred revenue	9,581	9,024
Asset retirement obligations	0	0
Other current liabilities	5,053	5,053
Total current liabilities	21,370	24,199
Long-term debt, less current installments	0	0
Workers' compensation, less current portion	0	0
Excess of black lung benefit obligation over trust assets	0	0
Postretirement medical benefits, less current portion	0	0
Pension and SERP obligations, less current portion	98	99
Deferred revenue, less current portion	38,325	41,297
Asset retirement obligations, less current portion	909	892
Intangible liabilities	5,339	5,606
Other liabilities	0	0
Intercompany receivable/payable	0	0
Total liabilities	66,041	72,093
Shareholders' deficit:
Preferred stock	0	0
Common stock	5	5
Other paid-in capital	52,842	52,835
Accumulated other comprehensive loss	(162)	(164)
Accumulated earnings (deficit)	49,272	55,915
Total equity (deficit)	101,957	108,591
Total Liabilities and Shareholders' Deficit	167,998	180,684
Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	8,794	7,942	6,698	5,362
Receivables:
Trade	22,857	17,389
Contractual third-party reclamation receivables	44	44
Intercompany receivable/payable	3,499	4,384
Other	244	2,974
Total receivables	26,644	24,791
Inventories	15,133	16,077
Deferred income taxes		870
Restricted investments and bond collateral	0	0
Other current assets	3,168	6,883
Total current assets	53,739	56,563
Property, plant and equipment:
Land and mineral rights	104,640	104,631
Plant and equipment	245,368	229,998
Gross property, plant and equipment	350,008	334,629
Less accumulated depreciation, depletion and amortization	138,718	132,189
Net property, plant and equipment	211,290	202,440
Advanced coal royalties	3,000	3,000
Reclamation deposits	0	0
Total restricted investments and bond collateral, less current portion	36,615	36,619
Contractual third-party reclamation receivables	302	293
Intangible assets	0	0
Investment in subsidiaries	0	0
Other assets	569	586
Total Assets	305,515	299,501
Current liabilities
Current installments of long-term debt	4,596	2,790
Accounts payable and accrued expenses:
Trade	14,710	12,522
Production taxes	22,442	17,429
Workers' compensation	0	0
Postretirement medical benefits	329	329
SERP	0	0
Deferred revenue	4,813	3,969
Asset retirement obligations	3,554	3,104
Other current liabilities	0	317
Total current liabilities	50,444	40,460
Long-term debt, less current installments	12,912	2,664
Workers' compensation, less current portion	0	0
Excess of black lung benefit obligation over trust assets	0	0
Postretirement medical benefits, less current portion	50,472	49,418
Pension and SERP obligations, less current portion	9,494	9,381
Deferred revenue, less current portion	0	0
Asset retirement obligations, less current portion	51,300	50,472
Intangible liabilities	0	0
Other liabilities	0	6,220
Intercompany receivable/payable	(4,326)	525
Total liabilities	170,296	159,140
Shareholders' deficit:
Preferred stock	0	0
Common stock	110	110
Other paid-in capital	92,896	94,370
Accumulated other comprehensive loss	17,372	17,492
Accumulated earnings (deficit)	24,841	28,389
Total equity (deficit)	135,219	140,361
Total Liabilities and Shareholders' Deficit	305,515	299,501
Non-Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	20,304	24,501	18,376	6,867
Receivables:
Trade	29,402	35,873
Contractual third-party reclamation receivables	8,169	8,443
Intercompany receivable/payable	(33,946)	(33,681)
Other	681	1,831
Total receivables	4,306	12,466
Inventories	18,469	17,735
Deferred income taxes		0
Restricted investments and bond collateral	0	0
Other current assets	6,005	5,049
Total current assets	49,084	59,751
Property, plant and equipment:
Land and mineral rights	172,163	172,163
Plant and equipment	202,923	202,886
Gross property, plant and equipment	375,086	375,049
Less accumulated depreciation, depletion and amortization	246,079	239,302
Net property, plant and equipment	129,007	135,747
Advanced coal royalties	4,263	4,311
Reclamation deposits	75,315	74,921
Total restricted investments and bond collateral, less current portion	17,483	17,482
Contractual third-party reclamation receivables	87,734	88,010
Intangible assets	228	238
Investment in subsidiaries	3,770	3,770
Other assets	4,493	3,098
Total Assets	371,377	387,328
Current liabilities
Current installments of long-term debt	21,205	21,161
Accounts payable and accrued expenses:
Trade	32,557	30,743
Production taxes	23,947	24,472
Workers' compensation	0	0
Postretirement medical benefits	1,583	1,583
SERP	0	0
Deferred revenue	1,640	1,075
Asset retirement obligations	18,673	20,250
Other current liabilities	172	142
Total current liabilities	99,777	99,426
Long-term debt, less current installments	64,848	70,248
Workers' compensation, less current portion	0	0
Excess of black lung benefit obligation over trust assets	0	0
Postretirement medical benefits, less current portion	35,356	35,098
Pension and SERP obligations, less current portion	1,011	1,627
Deferred revenue, less current portion	4,974	5,271
Asset retirement obligations, less current portion	206,827	205,147
Intangible liabilities	0	0
Other liabilities	1,063	1,450
Intercompany receivable/payable	5,633	6,434
Total liabilities	419,489	424,701
Shareholders' deficit:
Preferred stock	0	0
Common stock	132	132
Other paid-in capital	66,027	64,401
Accumulated other comprehensive loss	(13,937)	(14,153)
Accumulated earnings (deficit)	(100,334)	(87,753)
Total equity (deficit)	(48,112)	(37,373)
Total Liabilities and Shareholders' Deficit	371,377	387,328
Consolidating Adjustments
Current assets:
Cash and cash equivalents	0	0	20,608	0
Receivables:
Trade	0	0
Contractual third-party reclamation receivables	0	0
Intercompany receivable/payable	32,710	32,865
Other	(31)	(24)
Total receivables	32,679	32,841
Inventories	0	(1)
Deferred income taxes		(870)
Restricted investments and bond collateral	0	0
Other current assets	1	0
Total current assets	32,680	31,970
Property, plant and equipment:
Land and mineral rights	0	(1)
Plant and equipment	0	1
Gross property, plant and equipment	0	0
Less accumulated depreciation, depletion and amortization	(1)	(1)
Net property, plant and equipment	1	1
Advanced coal royalties	0	0
Reclamation deposits	0	0
Total restricted investments and bond collateral, less current portion	0	0
Contractual third-party reclamation receivables	0	0
Intangible assets	0	(1)
Investment in subsidiaries	(241,696)	(270,617)
Other assets	(3,500)	(2,000)
Total Assets	(212,515)	(240,647)
Current liabilities
Current installments of long-term debt	0	0
Accounts payable and accrued expenses:
Trade	0	1
Production taxes	0	1
Workers' compensation	0	0
Postretirement medical benefits	1	1
SERP	0	0
Deferred revenue	0	0
Asset retirement obligations	0	(1)
Other current liabilities	(31)	(24)
Total current liabilities	(30)	(22)
Long-term debt, less current installments	(3,500)	(2,000)
Workers' compensation, less current portion	0	0
Excess of black lung 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	(1)
Asset retirement obligations, less current portion	0	0
Intangible liabilities	0	0
Other liabilities	0	(6,220)
Intercompany receivable/payable	(19,920)	(20,825)
Total liabilities	(23,450)	(29,068)
Shareholders' deficit:
Preferred stock	0	0
Common stock	(247)	(247)
Other paid-in capital	(211,766)	(211,606)
Accumulated other comprehensive loss	(3,273)	(3,175)
Accumulated earnings (deficit)	26,221	3,449
Total equity (deficit)	(189,065)	(211,579)
Total Liabilities and Shareholders' Deficit	$ (212,515)	$ (240,647)