Segment Information (Schedule Of Operating Segment Results) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Segment Reporting Information [Line Items]
Revenues	$ 1,063,538	$ 985,528	$ 2,103,189	$ 1,858,466
Income (loss) from operations	(588,984)	95,354	(534,903)	197,592
Total assets	9,953,938	10,256,548	9,953,938	10,256,548	10,213,959
Depreciation, depletion and amortization	132,868	97,236	272,834	180,773
Amortization of acquired sales contacts, net	(4,451)	1,262	(18,468)	7,206
Mine closure and asset impairment costs	525,762		525,762
Capital expenditures	108,802	69,014	202,073	107,725
PRB [Member]
Segment Reporting Information [Line Items]
Revenues	322,512	391,413	723,689	784,526
Income (loss) from operations	22,747	35,615	55,290	82,489
Total assets	2,044,743	2,231,636	2,044,743	2,231,636
Depreciation, depletion and amortization	37,131	41,165	78,354	82,856
Amortization of acquired sales contacts, net	31	5,603	(785)	11,547
Capital expenditures	5,793	15,647	9,779	18,485
APP [Member]
Segment Reporting Information [Line Items]
Revenues	504,309	400,795	973,367	725,181
Income (loss) from operations	(493,093)	87,961	(477,258)	142,356
Total assets	3,870,734	4,694,368	3,870,734	4,694,368
Depreciation, depletion and amortization	73,176	33,091	149,193	54,107
Amortization of acquired sales contacts, net	(4,859)	(4,206)	(17,947)	(4,206)
Mine closure and asset impairment costs	525,916		525,916
Capital expenditures	78,102	29,288	144,405	46,590
WBIT [Member]
Segment Reporting Information [Line Items]
Revenues	199,552	189,154	344,111	344,593
Income (loss) from operations	13,779	43,673	45,020	70,564
Total assets	715,362	674,765	715,362	674,765
Depreciation, depletion and amortization	18,454	22,099	37,054	42,628
Mine closure and asset impairment costs	179		179
Capital expenditures	14,114	10,115	29,251	21,892
Other [Member]
Segment Reporting Information [Line Items]
Revenues	37,165	4,169	62,022	4,166
Income (loss) from operations	1,291	113	(2,459)	705
Total assets	580,272	562,291	580,272	562,291
Depreciation, depletion and amortization	3,423	536	7,110	357
Amortization of acquired sales contacts, net	377	(135)	264	(135)
Mine closure and asset impairment costs	(227)		(227)
Capital expenditures	(1,131)	4,373	4,513	4,373
Corporate, Other and Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(3)
Income (loss) from operations	(133,708)	(72,008)	(155,496)	(98,522)
Total assets	2,742,827	2,093,488	2,742,827	2,093,488
Depreciation, depletion and amortization	684	345	1,123	825
Mine closure and asset impairment costs	(106)		(106)
Capital expenditures	$ 11,924	$ 9,591	$ 14,125	$ 16,385