Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents	$ 439,655	$ 734,231
Short term investments	249,754	248,954
Restricted cash	43,563	5,678
Trade accounts receivable	204,593	211,506
Other receivables	14,948	20,511
Inventories	223,929	190,253
Prepaid royalties	9,006	11,118
Deferred income taxes	47,277	52,728
Coal derivative assets	13,358	13,257
Other current assets	50,838	54,515
Total current assets	1,296,921	1,542,751
Property, plant and equipment, net	6,341,026	6,453,458
Other assets
Prepaid royalties	52,956	66,806
Equity investments	227,788	235,842
Other noncurrent assets	117,664	130,866
Total other assets	398,408	433,514
Total assets	8,036,355	8,429,723
Current liabilities
Accounts payable	156,725	180,113
Accrued expenses and other current liabilities	262,958	302,396
Current maturities of debt	31,763	36,885
Total current liabilities	451,446	519,394
Long-term debt	5,114,581	5,123,485
Asset retirement obligations	409,435	398,896
Accrued pension benefits	13,580	16,260
Accrued postretirement benefits other than pension	34,176	32,668
Accrued workers’ compensation	97,489	94,291
Deferred income taxes	411,930	422,809
Other noncurrent liabilities	109,693	153,766
Total liabilities	6,642,330	6,761,569
Stockholders' equity
Common stock, $0.01 par value, authorized 260,000 shares, issued 214,433 shares and 213,791 shares at June 30, 2015 and December 31, 2014, respectively	2,145	2,141
Paid-in capital	3,051,805	3,048,460
Treasury stock, at cost, 1,517 shares at June 30, 2015 and December 31, 2014	(53,863)	(53,863)
Accumulated deficit	(1,613,123)	(1,331,825)
Accumulated other comprehensive income	7,061	3,241
Total stockholders’ equity	1,394,025	1,668,154
Total liabilities and stockholders’ equity	$ 8,036,355	$ 8,429,723