Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current assets
Cash and cash equivalents	$ 734,231	$ 911,099
Short term investments	248,954	248,414
Trade accounts receivable	211,506	198,020
Other receivables	20,511	31,553
Inventories	190,253	264,161
Prepaid royalties	11,118	8,083
Deferred income taxes	52,728	49,144
Coal derivative assets	13,257	14,851
Other current assets	60,193	56,746
Total current assets	1,542,751	1,782,071
Property, plant and equipment
Coal lands and mineral rights	6,040,656	5,991,719
Plant and equipment	2,935,381	2,882,486
Deferred mine development	891,649	979,270
Property, plant and equipment, gross	9,867,686	9,853,475
Less accumulated depreciation, depletion and amortization	(3,414,228)	(3,119,189)
Property, plant and equipment, net	6,453,458	6,734,286
Other assets
Prepaid royalties	66,806	87,577
Equity investments	235,842	221,456
Other noncurrent assets	130,866	164,803
Total other assets	433,514	473,836
Total assets	8,429,723	8,990,193
Current liabilities
Accounts payable	180,113	176,142
Accrued expenses and other current liabilities	302,396	278,587
Current maturities of debt	36,885	33,493
Total current liabilities	519,394	488,222
Long-term debt	5,123,485	5,118,002
Asset retirement obligations	398,896	402,713
Accrued pension benefits	16,260	7,111
Accrued postretirement benefits other than pension	32,668	39,255
Accrued workers’ compensation	94,291	78,062
Deferred income taxes	422,809	413,546
Other noncurrent liabilities	153,766	190,033
Total liabilities	6,761,569	6,736,944
Stockholders' equity
Common stock, $0.01 par value, authorized 260,000 shares, issued 213,791 and 213,792 shares at December 31, 2014 and 2013, respectively	2,141	2,141
Paid-in capital	3,048,460	3,038,613
Treasury stock, at cost	(53,863)	(53,848)
Accumulated deficit	(1,331,825)	(771,349)
Accumulated other comprehensive income	3,241	37,692
Total stockholders’ equity	1,668,154	2,253,249
Total liabilities and stockholders’ equity	$ 8,429,723	$ 8,990,193