Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents	$ 450,781	$ 734,231
Short term investments	200,192	248,954
Restricted cash	97,542	5,678
Trade accounts receivable (net of allowance for doubtful accounts of $7.8 million and $0.2 million, respectively)	117,405	211,506
Other receivables	18,362	20,511
Inventories	196,720	190,253
Prepaid royalties	10,022	11,118
Deferred income taxes	0	52,728
Coal derivative assets	8,035	13,257
Other current assets	104,723	54,515
Total current assets	1,203,782	1,542,751
Property, plant and equipment
Coal lands and mineral rights	3,713,639	6,040,656
Plant and equipment	2,359,674	2,935,381
Deferred mine development	553,286	891,649
Property, plant and equipment, gross	6,626,599	9,867,686
Less accumulated depreciation, depletion and amortization	(3,007,570)	(3,414,228)
Property, plant and equipment, net	3,619,029	6,453,458
Other assets
Prepaid royalties	23,671	66,806
Equity investments	201,877	235,842
Other noncurrent assets	58,379	130,866
Total other assets	283,927	433,514
Total assets	5,106,738	8,429,723
Current liabilities
Accounts payable	128,131	180,113
Accrued expenses and other current liabilities	329,450	302,396
Current maturities of debt	5,107,210	36,885
Total current liabilities	5,564,791	519,394
Long-term debt	30,953	5,123,485
Asset retirement obligations	396,659	398,896
Accrued pension benefits	27,373	16,260
Accrued postretirement benefits other than pension	99,810	32,668
Accrued workers’ compensation	112,270	94,291
Deferred income taxes	0	422,809
Other noncurrent liabilities	119,171	153,766
Total liabilities	6,351,027	6,761,569
Stockholders' equity (deficit)
Common stock, $0.01 par value, authorized 26,000 shares, issued 21,446 and 21,379 shares at December 31, 2015 and 2014, respectively	2,145	2,141
Paid-in capital	3,054,211	3,048,460
Treasury stock, at cost	(53,863)	(53,863)
Accumulated deficit	(4,244,967)	(1,331,825)
Accumulated other comprehensive income	(1,815)	3,241
Total stockholders’ equity (deficit)	(1,244,289)	1,668,154
Total liabilities and stockholders’ equity (deficit)	$ 5,106,738	$ 8,429,723