Supplemental Guarantor and Non-Guarantor Financial Information (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
ASSETS
Cash and cash equivalents	$ 116,601	$ 128,430	$ 293,410	$ 165,279
Receivables, net	256,967	313,343
Inventories	306,018	240,437
Deferred income taxes	58,526	61,079
Prepaid expenses	53,776	49,974
Other current assets	23,928	45,649
Total current assets	815,816	838,912
Mineral interests, net	2,965,557	3,056,258
Property, plant and equipment, net	1,732,131	1,631,333
Deferred income taxes	160,422	109,300
Goodwill		1,066,754
Other long-term assets	94,494	153,951
Total assets	5,768,420	6,856,508	1,657,765
LIABILITIES AND STOCKHOLDERS' EQUITY
Current debt	18,793	56,695
Accounts payable	114,913	112,661
Accrued expenses	184,875	229,067
Accumulated postretirement benefits obligation	29,200	27,247
Other current liabilities	206,473	63,757
Total current liabilities	554,254	489,427
Long-term debt	2,397,372	2,269,020
Deferred income taxes	921,687	1,029,336
Accumulated postretirement benefits obligation	633,264	550,671
Other long-term liabilities	251,272	381,537
Total liabilities	4,757,849	4,719,991
Total stockholders' equity	1,010,571	2,136,517	595,066	259,395
Total liabilities and stockholders' equity	5,768,420	6,856,508
Parent (Issuer)
ASSETS
Cash and cash equivalents	83,833	99,086	294,413	164,666
Receivables, net	64,106	45,244
Deferred income taxes	39,375	11,698
Prepaid expenses	1,869	1,187
Other current assets	17,559	15,184
Total current assets	206,742	172,399
Property, plant and equipment, net	8,448	5,459
Deferred income taxes	52,363	59,705
Other long-term assets	3,601,716	4,603,800
Total assets	3,869,269	4,841,363
LIABILITIES AND STOCKHOLDERS' EQUITY
Accounts payable	5,128	245,790
Accrued expenses	262,704	34,027
Accumulated postretirement benefits obligation	131	192
Other current liabilities	157,044	20,809
Total current liabilities	425,007	300,818
Long-term debt	2,381,255	2,208,163
Accumulated postretirement benefits obligation	452	355
Other long-term liabilities	51,984	195,510
Total liabilities	2,858,698	2,704,846
Total stockholders' equity	1,010,571	2,136,517
Total liabilities and stockholders' equity	3,869,269	4,841,363
Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	61	79	(1,823)	(579)
Receivables, net	620,701	344,460
Inventories	131,893	129,015
Deferred income taxes	17,687	38,834
Prepaid expenses	45,327	39,317
Other current assets	1,109	4,225
Total current assets	816,778	555,930
Mineral interests, net	18,475	29,461
Property, plant and equipment, net	790,900	777,882
Deferred income taxes	112,560	67,145
Goodwill		1,713
Other long-term assets	9,375	13,730
Total assets	1,748,088	1,445,861
LIABILITIES AND STOCKHOLDERS' EQUITY
Current debt	10,196	29,063
Accounts payable	78,260	72,018
Accrued expenses	83,155	72,687
Accumulated postretirement benefits obligation	29,069	27,055
Other current liabilities	24,389	7,398
Total current liabilities	225,069	208,221
Long-term debt	1,784	10,885
Accumulated postretirement benefits obligation	632,812	550,316
Other long-term liabilities	128,593	133,295
Total liabilities	988,258	902,717
Total stockholders' equity	759,830	543,144
Total liabilities and stockholders' equity	1,748,088	1,445,861
Non-Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	32,707	29,265	820	1,192
Receivables, net	79,679	167,462
Inventories	174,125	111,422
Deferred income taxes	1,464	10,547
Prepaid expenses	6,580	9,470
Other current assets	5,260	26,240
Total current assets	299,815	354,406
Mineral interests, net	2,947,082	3,026,797
Property, plant and equipment, net	932,783	847,992
Deferred income taxes	(4,501)	(17,550)
Goodwill		1,065,041
Other long-term assets	13,497	20,976
Total assets	4,188,676	5,297,662
LIABILITIES AND STOCKHOLDERS' EQUITY
Current debt	8,597	27,632
Accounts payable	31,525	38,676
Accrued expenses	346,535	122,353
Other current liabilities	25,040	35,550
Total current liabilities	411,697	224,211
Long-term debt	14,333	49,972
Deferred income taxes	921,687	1,029,336
Other long-term liabilities	70,695	52,732
Total liabilities	1,418,412	1,356,251
Total stockholders' equity	2,770,264	3,941,411
Total liabilities and stockholders' equity	4,188,676	5,297,662
Eliminations
ASSETS
Receivables, net	(507,519)	(243,823)
Total current assets	(507,519)	(243,823)
Other long-term assets	(3,530,094)	(4,484,555)
Total assets	(4,037,613)	(4,728,378)
LIABILITIES AND STOCKHOLDERS' EQUITY
Accounts payable		(243,823)
Accrued expenses	(507,519)
Total current liabilities	(507,519)	(243,823)
Total liabilities	(507,519)	(243,823)
Total stockholders' equity	(3,530,094)	(4,484,555)
Total liabilities and stockholders' equity	$ (4,037,613)	$ (4,728,378)