Segment Information (Schedule Of Operating Segment Results) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ 742,180	$ 791,269	$ 2,191,927	$ 2,294,971
Income (loss) from operations	(35,300)	(234,753)	(144,227)	(322,463)
Depreciation, depletion and amortization	105,155	106,323	312,042	327,601
Amortization of acquired sales contracts, net	(3,013)	(2,568)	(9,948)	(7,587)
Asset impairment and mine closure costs	5,060	200,397	6,572	220,879
Capital expenditures	22,955	54,104	118,701	223,168
PRB [Member]
Segment Reporting Information [Line Items]
Revenues	389,386	420,521	1,106,258	1,135,892
Income (loss) from operations	18,797	20,694	19,001	53,244
Depreciation, depletion and amortization	43,962	46,619	124,243	130,993
Amortization of acquired sales contracts, net	(1,200)	(864)	(2,774)	(3,004)
Asset impairment and mine closure costs	0	0	0	0
Capital expenditures	8,174	1,695	17,230	5,671
APP [Member]
Segment Reporting Information [Line Items]
Revenues	272,354	263,189	832,452	883,485
Income (loss) from operations	(35,888)	(157,883)	(79,890)	(190,278)
Depreciation, depletion and amortization	48,867	46,530	155,087	157,867
Amortization of acquired sales contracts, net	(1,815)	(2,691)	(7,266)	(7,975)
Asset impairment and mine closure costs	5,060	126,449	5,060	126,449
Capital expenditures	9,039	44,624	28,232	137,390
Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	80,440	107,559	253,217	275,594
Income (loss) from operations	17,912		34,640
Depreciation, depletion and amortization	10,499	11,958	29,601	34,319
Amortization of acquired sales contracts, net	2	987	92	3,392
Asset impairment and mine closure costs	0	16,280	0	16,280
Capital expenditures	4,678	7,122	8,837	17,923
Corporate, Other and Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues
Income (loss) from operations	(36,121)	(97,620)	(117,978)	(208,788)
Depreciation, depletion and amortization	1,827	1,216	3,111	4,422
Amortization of acquired sales contracts, net	0	0	0	0
Asset impairment and mine closure costs	0	57,668	1,512	78,150
Capital expenditures	$ 1,064	$ 663	$ 64,402	$ 62,184