Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current assets
Cash and cash equivalents	$ 784,622	$ 138,149
Restricted cash	3,453	10,322
Short term investments	234,305
Trade accounts receivable	247,539	380,595
Other receivables	84,541	88,584
Inventories	365,424	377,490
Prepaid royalties	11,416	21,944
Deferred income taxes	67,360	42,051
Coal derivative assets	22,975	13,335
Other	92,469	110,304
Total current assets	1,914,104	1,182,774
Coals, lands and mineral rights	6,218,776	6,578,430
Plant and Equipment	3,391,265	3,225,985
Deferred mine development	1,079,856	1,064,279
Property, Plant and Equipment	10,689,897	10,868,694
Less: Accumulated Depreciation, Depletion and Amortization	(3,352,799)	(2,919,544)
Property, plant and equipment, net	7,337,098	7,949,150
Other assets
Prepaid royalties	87,773	86,626
Goodwill	265,423	596,103
Equity investments	242,215	225,605
Other	160,164	173,701
Total other assets	755,575	1,082,035
Total assets	10,006,777	10,213,959
Current liabilities
Accounts payable	224,418	383,782
Coal derivative liabilities	1,737	7,828
Accrued expenses and other current liabilities	318,018	348,207
Current maturities of debt and short-term borrowings	32,896	280,851
Total current liabilities	577,069	1,020,668
Long-term debt	5,085,879	3,762,297
Asset retirement obligations	409,705	446,784
Accrued pension benefits	67,630	48,244
Accrued postretirement benefits other than pension	45,086	42,309
Accrued workers' compensation	81,629	71,948
Deferred income taxes	664,182	976,753
Other noncurrent liabilities	221,030	255,382
Total liabilities	7,152,210	6,624,385
Redeemable noncontrolling interest		11,534
Stockholders' Equity
Common stock	2,141	2,136
Paid-in capital	3,026,823	3,015,349
Treasury stock, at cost	(53,848)	(53,848)
Retained earnings	(104,042)	622,353
Accumulated other comprehensive loss	(16,507)	(7,950)
Total stockholders' equity	2,854,567	3,578,040
Total liabilities and stockholders' equity	$ 10,006,777	$ 10,213,959