Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current assets
Cash and cash equivalents	$ 550,756	$ 138,149
Restricted cash	3,450	10,322
Short term investments	99,359
Trade accounts receivable	277,634	380,595
Other receivables	71,114	88,584
Inventories	391,526	377,490
Prepaid royalties	12,120	21,944
Deferred income taxes	65,395	42,051
Coal derivative assets	40,837	13,335
Other	67,495	110,304
Total current assets	1,579,686	1,182,774
Property, plant and equipment, net	7,372,063	7,949,150
Other assets
Prepaid royalties	85,842	86,626
Goodwill	480,312	596,103
Equity investments	237,645	225,605
Other	180,306	173,701
Total other assets	984,105	1,082,035
Total assets	9,935,854	10,213,959
Current liabilities
Accounts payable	304,442	383,782
Coal derivative liabilities	3,498	7,828
Accrued expenses and other current liabilities	355,448	348,207
Current maturities of debt and short-term borrowings	115,695	280,851
Total current liabilities	779,083	1,020,668
Long-term debt	4,465,445	3,762,297
Asset retirement obligations	426,044	446,784
Accrued pension benefits	45,160	48,244
Accrued postretirement benefits other than pension	41,061	42,309
Accrued workers' compensation	85,251	71,948
Deferred income taxes	746,079	976,753
Other noncurrent liabilities	182,464	255,382
Total liabilities	6,770,587	6,624,385
Redeemable noncontrolling interest		11,534
Stockholders' Equity
Common stock	2,141	2,136
Paid-in capital	3,024,435	3,015,349
Treasury stock, at cost	(53,848)	(53,848)
Retained earnings	197,749	622,353
Accumulated other comprehensive loss	(5,210)	(7,950)
Total stockholders' equity	3,165,267	3,578,040
Total liabilities and stockholders' equity	$ 9,935,854	$ 10,213,959