CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
ASSETS
Cash and cash equivalents	$ 170,878	$ 116,601
Receivables, net	254,256	256,967
Inventories	339,584	306,018
Deferred income taxes	55,318	58,526
Prepaid expenses	60,151	53,776
Other current assets	23,754	23,928
Total current assets	903,941	815,816
Mineral interests, net of accumulated depletion of $218.8 million and $179.6 million, respectively	2,914,825	2,965,557
Property, plant and equipment, net of accumulated depreciation of $890.2 million and $796.7 million, respectively	1,657,123	1,732,131
Deferred income taxes	161,215	160,422
Other long-term assets	94,752	94,494
Total assets	5,731,856	5,768,420
LIABILITIES AND STOCKHOLDERS' EQUITY
Current debt	14,919	18,793
Accounts payable	123,540	114,913
Accrued expenses	135,772	184,875
Accumulated postretirement benefits obligation	30,074	29,200
Other current liabilities	202,300	206,473
Total current liabilities	506,605	554,254
Long-term debt	2,591,181	2,397,372
Accumulated postretirement benefits obligation	638,713	633,264
Deferred income taxes	848,748	921,687
Other long-term liabilities	237,320	251,272
Total liabilities	4,822,567	4,757,849
Commitments and contingencies (Note 8)
Stockholders' equity:
Common stock, $0.01 par value per share: Authorized-200,000,000 shares, Issued-62,571,807 and 62,521,300 shares, respectively	626	625
Capital in excess of par value	1,609,854	1,628,244
Accumulated deficit	(423,863)	(347,448)
Accumulated other comprehensive income (loss):
Pension and other postretirement benefit plans, net of tax	(256,725)	(266,042)
Foreign currency translation adjustment	(18,588)	(1,502)
Unrealized loss on hedges, net of tax	(2,955)	(4,203)
Unrealized investment gain, net of tax	940	897
Total stockholders' equity	909,289	1,010,571
Total liabilities and stockholders' equity	$ 5,731,856	$ 5,768,420