Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Current assets
Cash and cash equivalents	$ 512,527	$ 138,149
Restricted cash	5,740	10,322
Trade accounts receivable	327,402	380,595
Other receivables	70,103	88,584
Inventories	455,091	377,490
Prepaid royalties	11,214	21,944
Deferred income taxes	65,531	42,051
Coal derivative assets	53,351	13,335
Other	67,568	110,304
Total current assets	1,568,527	1,182,774
Property, plant and equipment, net	7,397,131	7,949,150
Other assets
Prepaid royalties	89,441	86,626
Goodwill	480,312	596,103
Equity investments	235,299	225,605
Other	183,228	173,701
Total other assets	988,280	1,082,035
Total assets	9,953,938	10,213,959
Current liabilities
Accounts payable	316,669	383,782
Coal derivative liabilities	7,090	7,828
Accrued expenses and other current liabilities	360,793	348,207
Current maturities of debt and short-term borrowings	111,260	280,851
Total current liabilities	795,812	1,020,668
Long-term debt	4,464,351	3,762,297
Asset retirement obligations	424,289	446,784
Accrued pension benefits	49,040	48,244
Accrued postretirement benefits other than pension	42,028	42,309
Accrued workers' compensation	82,372	71,948
Deferred income taxes	730,495	976,753
Other noncurrent liabilities	223,131	255,382
Total liabilities	6,811,518	6,624,385
Redeemable noncontrolling interest	17,500	11,534
Stockholders' Equity
Common stock	2,138	2,136
Paid-in capital	3,022,014	3,015,349
Treasury stock, at cost	(53,848)	(53,848)
Retained earnings	158,374	622,353
Accumulated other comprehensive loss	(3,758)	(7,950)
Total stockholders' equity	3,124,920	3,578,040
Total liabilities and stockholders' equity	$ 9,953,938	$ 10,213,959