Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 911,099	$ 784,622
Restricted cash		3,453
Short term investments	248,414	234,305
Trade accounts receivable	198,020	247,539
Other receivables	31,553	84,541
Inventories	264,161	365,424
Prepaid royalties	8,083	11,416
Deferred income taxes	49,144	67,360
Other current assets	56,746	92,469
Total current assets	1,782,071	1,914,104
Property, plant and equipment
Coal lands and mineral rights	5,991,719	6,218,776
Plant and equipment	2,882,486	3,391,265
Deferred mine development	979,270	1,079,856
Property, Plant and Equipment, Gross	9,853,475	10,689,897
Less accumulated depreciation, depletion and amortization	(3,119,189)	(3,352,799)
Property, plant and equipment, net	6,734,286	7,337,098
Other assets
Prepaid royalties	87,577	87,773
Goodwill	0	265,423
Equity investments	221,456	242,215
Other noncurrent assets	164,803	160,164
Total other assets	473,836	755,575
Total assets	8,990,193	10,006,777
Current liabilities
Accounts payable	176,142	224,418
Accrued expenses and other current liabilities	278,575	318,018
Current maturities of debt	33,493	32,896
Total current liabilities	488,222	577,069
Long-term debt	5,118,002	5,085,879
Asset retirement obligations	402,713	409,705
Accrued pension benefits	7,111	67,630
Accrued postretirement benefits other than pension	39,255	45,086
Accrued workers’ compensation	78,062	81,629
Deferred income taxes	413,546	664,182
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent	(413,546)	(664,182)
Other noncurrent liabilities	190,033	221,030
Total liabilities	6,736,944	7,152,210
Stockholders' equity
Common stock, $0.01 par value, authorized 260,000 shares, issued 213,792 and 213,759 shares at December 31, 2013 and December 31, 2012, respectively	2,141	2,141
Paid-in capital	3,038,613	3,026,823
Treasury stock, at cost	(53,848)	(53,848)
Accumulated deficit	(771,349)	(104,042)
Accumulated other comprehensive income (loss)	37,692	(16,507)
Total stockholders’ equity	2,253,249	2,854,567
Total liabilities and stockholders’ equity	8,990,193	10,006,777
Coal Contract [Member]
Current assets
Coal derivative assets	14,851	22,975
Current liabilities
Coal derivative assets	$ 12	$ 1,737