Segment Information (Schedule Of Operating Segment Results) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$ 791,269	$ 975,170	$ 2,294,971	$ 2,901,092
Income (loss) from operations	(234,753)	119,242	(322,463)	(449,854)
Depreciation, depletion and amortization	106,323	118,942	327,601	374,631
Amortization of acquired sales contracts, net	(2,568)	(4,093)	(7,587)	(22,561)
Asset impairment and mine closure costs	200,397	(2,144)	220,879	523,439
Total assets	9,531,455	9,935,854	9,531,455	9,935,854	10,006,777
Capital expenditures	54,104	101,895	223,168	303,968
PRB [Member]
Segment Reporting Information [Line Items]
Revenues	420,521	406,719	1,135,892	1,130,408
Income (loss) from operations	20,694	38,873	53,244	94,163
Depreciation, depletion and amortization	46,619	43,944	130,993	122,298
Amortization of acquired sales contracts, net	(864)	(589)	(3,004)	(1,374)
Asset impairment and mine closure costs
Total assets	1,897,218	2,234,941	1,897,218	2,234,941
Capital expenditures	1,695	5,620	5,671	15,399
APP [Member]
Segment Reporting Information [Line Items]
Revenues	263,188	436,409	883,484	1,409,776
Income (loss) from operations	(157,883)	88,695	(190,278)	(388,563)
Depreciation, depletion and amortization	46,529	61,596	157,866	210,789
Amortization of acquired sales contracts, net	(2,691)	(3,711)	(7,975)	(21,658)
Asset impairment and mine closure costs	126,449	(1,801)	126,449	524,115
Total assets	4,141,072	4,130,273	4,141,072	4,130,273
Capital expenditures	44,624	77,772	137,390	222,177
WBIT [Member]
Segment Reporting Information [Line Items]
Revenues	78,022	105,515	187,374	272,359
Income (loss) from operations	9,287	24,110	23,766	34,937
Depreciation, depletion and amortization	9,436	9,985	26,528	29,894
Amortization of acquired sales contracts, net
Asset impairment and mine closure costs
Total assets	146,947	676,057	146,947	676,057
Capital expenditures	5,859	13,510	13,147	42,761
Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	29,538	26,527	88,221	88,549
Income (loss) from operations	(9,231)	(1,298)	(407)	(3,757)
Depreciation, depletion and amortization	2,523	2,594	7,792	9,704
Amortization of acquired sales contracts, net	987	207	3,392	471
Asset impairment and mine closure costs	16,280	(210)	16,280	(437)
Total assets	137,941	169,981	137,941	169,981
Capital expenditures	1,263	3,640	4,776	8,153
Corporate, Other and Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues
Income (loss) from operations	(97,620)	(31,138)	(208,788)	(186,634)
Depreciation, depletion and amortization	1,216	823	4,422	1,946
Amortization of acquired sales contracts, net
Asset impairment and mine closure costs	57,668	(133)	78,150	(239)
Total assets	3,208,277	2,724,602	3,208,277	2,724,602
Capital expenditures	$ 663	$ 1,353	$ 62,184	$ 15,478