Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current assets
Cash and cash equivalents	$ 740,154	$ 911,099
Short term investments	248,647	248,414
Trade accounts receivable	203,782	198,020
Other receivables	35,369	31,553
Inventories	228,726	264,161
Prepaid royalties	7,932	8,083
Deferred income taxes	48,786	49,144
Coal derivative assets	14,122	14,851
Other current assets	54,270	56,746
Total current assets	1,581,788	1,782,071
Property, plant and equipment, net	6,603,458	6,734,286
Other assets
Prepaid royalties	87,494	87,577
Equity investments	229,514	221,456
Other noncurrent assets	153,854	164,803
Total other assets	470,862	473,836
Total assets	8,656,108	8,990,193
Current liabilities
Accounts payable	160,209	176,142
Accrued expenses and other current liabilities	294,317	278,587
Current maturities of debt	27,266	33,493
Total current liabilities	481,792	488,222
Long-term debt	5,116,353	5,118,002
Asset retirement obligations	395,813	402,713
Accrued pension benefits	13,925	7,111
Accrued postretirement benefits other than pension	38,034	39,255
Accrued workers’ compensation	74,083	78,062
Deferred income taxes	332,207	413,546
Other noncurrent liabilities	172,512	190,033
Total liabilities	6,624,719	6,736,944
Stockholders' equity
Common stock, $0.01 par value, authorized 260,000 shares, issued 213,792 shares at both June 30, 2014 and December 31, 2013.	2,141	2,141
Paid-in capital	3,044,082	3,038,613
Treasury stock, at cost	(53,848)	(53,848)
Accumulated deficit	(994,471)	(771,349)
Accumulated other comprehensive income	33,485	37,692
Total stockholders’ equity	2,031,389	2,253,249
Total liabilities and stockholders’ equity	$ 8,656,108	$ 8,990,193