Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Current assets
Cash and cash equivalents	$ 117,770	$ 138,149
Restricted cash	8,866	10,322
Trade accounts receivable	295,012	380,595
Other receivables	66,702	88,584
Inventories	488,686	377,490
Prepaid royalties	18,025	21,944
Deferred income taxes	65,531	42,051
Coal derivative assets	22,043	13,335
Other	96,484	110,304
Total current assets	1,179,119	1,182,774
Property, plant and equipment, net	7,892,733	7,949,150
Other assets
Prepaid royalties	90,221	86,626
Goodwill	596,103	596,103
Equity investments	230,519	225,605
Other	176,423	173,701
Total other assets	1,093,266	1,082,035
Total assets	10,165,118	10,213,959
Current liabilities
Accounts payable	294,341	383,782
Coal derivative liabilities	9,100	7,828
Accrued expenses and other current liabilities	357,386	348,207
Current maturities of debt and short-term borrowings	102,356	280,851
Total current liabilities	763,183	1,020,668
Long-term debt	3,967,796	3,762,297
Asset retirement obligations	432,620	446,784
Accrued pension benefits	49,378	48,244
Accrued postretirement benefits other than pension	42,784	42,309
Accrued workers' compensation	74,012	71,948
Deferred income taxes	982,596	976,753
Other noncurrent liabilities	268,585	255,382
Total liabilities	6,580,954	6,624,385
Redeemable noncontrolling interest	11,739	11,534
Stockholders' Equity
Common stock	2,141	2,136
Paid-in capital	3,024,553	3,015,349
Treasury stock, at cost	(53,848)	(53,848)
Retained earnings	600,230	622,353
Accumulated other comprehensive loss	(651)	(7,950)
Total stockholders' equity	3,572,425	3,578,040
Total liabilities and stockholders' equity	$ 10,165,118	$ 10,213,959