CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
ASSETS
Cash and cash equivalents	$ 138,200	$ 128,430
Receivables, net	293,674	313,343
Inventories	309,742	240,437
Deferred income taxes	58,894	61,079
Prepaid expenses	44,226	49,974
Other current assets	39,242	45,649
Total current assets	883,978	838,912
Mineral interests, net of accumulated depletion of $108.8 million and $84.2 million, respectively	3,034,630	3,056,258
Property, plant and equipment, net of accumulated depreciation of $662.0 million and $614.6 million, respectively	1,678,957	1,631,333
Deferred income taxes	109,868	109,300
Goodwill	1,066,754	1,066,754
Other long-term assets	138,081	153,951
Total assets	6,912,268	6,856,508
LIABILITIES AND STOCKHOLDERS' EQUITY
Current debt	69,144	56,695
Accounts payable	125,494	112,661
Accrued expenses	194,477	229,067
Accumulated postretirement benefits obligation	27,714	27,247
Other current liabilities	55,953	63,757
Total current liabilities	472,782	489,427
Long-term debt	2,312,858	2,269,020
Deferred income taxes	1,018,333	1,029,336
Accumulated postretirement benefits obligation	553,863	550,671
Other long-term liabilities	379,236	381,537
Total liabilities	4,737,072	4,719,991
Commitments and contingencies (Note 9)
Stockholders' equity:
Common stock, $0.01 par value per share: Authorized-200,000,000 shares, Issued-62,481,923 and 62,444,905 shares, respectively	625	624
Preferred stock, $0.01 par value per share: Authorized-20,000,000 shares, issued-0 shares
Capital in excess of par value	1,622,279	1,620,430
Retained earnings	777,103	744,939
Accumulated other comprehensive income (loss):
Pension and other postretirement benefit plans, net of tax	(221,643)	(225,541)
Foreign currency translation adjustment	(857)	(3,276)
Unrealized loss on hedges, net of tax	(2,070)	(787)
Unrealized investment gain (loss), net of tax	(241)	128
Total stockholders' equity	2,175,196	2,136,517
Total liabilities and stockholders' equity	$ 6,912,268	$ 6,856,508