CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
ASSETS
Cash and cash equivalents	$ 293,134	$ 116,601
Receivables, net	305,354	256,967
Inventories	320,681	306,018
Deferred income taxes	58,073	58,526
Prepaid expenses	47,097	53,776
Other current assets	20,778	23,928
Total current assets	1,045,117	815,816
Mineral interests, net of accumulated depletion of $232,065 and $179,595, respectively	2,917,902	2,965,557
Property, plant and equipment, net of accumulated depreciation of $925,650 and $796,683, respectively	1,628,441	1,732,131
Deferred income taxes	148,311	160,422
Other long-term assets	100,741	94,494
Total assets	5,840,512	5,768,420
LIABILITIES AND STOCKHOLDERS' EQUITY
Current debt	12,179	18,793
Accounts payable	97,693	114,913
Accrued expenses	154,470	184,875
Accumulated postretirement benefits obligation	30,511	29,200
Other current liabilities	214,300	206,473
Total current liabilities	509,153	554,254
Long-term debt	2,770,381	2,397,372
Accumulated postretirement benefits obligation	641,337	633,264
Deferred income taxes	854,408	921,687
Other long-term liabilities	236,555	251,272
Total liabilities	5,011,834	4,757,849
Commitments and contingencies (Note 8)
Stockholders' equity:
Common stock, $0.01 par value per share: Authorized-200,000,000 shares, Issued-62,576,365 and 62,521,300 shares, respectively	626	625
Capital in excess of par value	1,610,748	1,628,244
Accumulated deficit	(524,587)	(347,448)
Accumulated other comprehensive income (loss):
Pension and other postretirement benefit plans, net of tax	(252,066)	(266,042)
Foreign currency translation adjustment	(3,741)	(1,502)
Unrealized loss on hedges, net of tax	(2,302)	(4,203)
Unrealized investment gain, net of tax		897
Total stockholders' equity	828,678	1,010,571
Total liabilities and stockholders' equity	$ 5,840,512	$ 5,768,420