Segment Information (Schedule Of Operating Segment Results) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$ 766,332	$ 965,685	$ 1,503,702	$ 1,925,922
Income (loss) from operations	(36,279)	(596,893)	(87,710)	(569,096)
Depreciation, depletion and amortization	111,085	124,536	221,278	255,689
Amortization of acquired sales contracts, net	(2,209)	(4,451)	(5,019)	(18,468)
Asset impairment and mine closure costs	20,482	525,583	20,482	525,583
Total assets	9,730,729	9,953,938	9,730,729	9,953,938	10,006,777
Capital expenditures	114,542	108,802	169,064	202,073
PRB [Member]
Segment Reporting Information [Line Items]
Revenues	353,425	322,512	715,371	723,689
Income (loss) from operations	16,798	22,747	32,550	55,290
Depreciation, depletion and amortization	42,147	37,131	84,374	78,354
Amortization of acquired sales contracts, net	(941)	31	(2,140)	(785)
Asset impairment and mine closure costs
Total assets	1,954,828	2,044,743	1,954,828	2,044,743
Capital expenditures	1,819	5,793	3,976	9,779
APP [Member]
Segment Reporting Information [Line Items]
Revenues	337,678	504,309	620,296	973,367
Income (loss) from operations	(5,238)	(493,093)	(32,395)	(477,258)
Depreciation, depletion and amortization	56,006	73,176	111,337	149,193
Amortization of acquired sales contracts, net	(2,812)	(4,859)	(5,284)	(17,947)
Asset impairment and mine closure costs		525,916		525,916
Total assets	4,264,500	4,154,871	4,264,500	4,154,871
Capital expenditures	43,470	78,102	92,766	144,405
WBIT [Member]
Segment Reporting Information [Line Items]
Revenues	41,840	101,699	109,352	166,844
Income (loss) from operations	12,140	5,870	14,480	10,827
Depreciation, depletion and amortization	8,396	10,122	17,092	19,909
Amortization of acquired sales contracts, net
Asset impairment and mine closure costs
Total assets	651,884	715,362	651,884	715,362
Capital expenditures	5,786	14,114	7,288	29,251
Other [Member]
Segment Reporting Information [Line Items]
Revenues	33,389	37,165	58,683	62,022
Income (loss) from operations	1,167	1,291	(407)	(2,459)
Depreciation, depletion and amortization	2,660	3,423	5,269	7,110
Amortization of acquired sales contracts, net	1,544	377	2,405	264
Asset impairment and mine closure costs		(227)		(227)
Total assets	154,354	170,446	154,354	170,446
Capital expenditures	3,031	(1,131)	3,513	4,513
Corporate, Other and Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues
Income (loss) from operations	(61,146)	(133,708)	(101,938)	(155,496)
Depreciation, depletion and amortization	1,876	684	3,206	1,123
Amortization of acquired sales contracts, net
Asset impairment and mine closure costs	20,482		20,482	(106)
Total assets	2,705,163	2,868,516	2,705,163	2,868,516
Capital expenditures	$ 60,436	$ 11,924	$ 61,521	$ 14,125