Segment Information (Schedule Of Operating Segment Results) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Revenues	$ 420,298	$ 644,462	$ 848,404	$ 1,321,467
Adjusted EBITDA	(8,360)	45,328	(18,386)	127,100
Depreciation, depletion and amortization	58,459	97,372	122,158	202,246
Amortization of acquired sales contracts, net	1	(1,644)	(832)	(5,034)
Capital expenditures	68,211	76,481	74,137	99,361
Operating Segments [Member] | PRB [Member]
Segment Reporting Information [Line Items]
Revenues	207,735	342,480	430,857	733,686
Adjusted EBITDA	15,932	56,654	22,942	128,716
Depreciation, depletion and amortization	30,145	42,711	62,905	87,072
Amortization of acquired sales contracts, net	76	(761)	30	(2,046)
Capital expenditures	489	4,425	499	21,394
Operating Segments [Member] | APP [Member]
Segment Reporting Information [Line Items]
Revenues	170,940	224,298	344,558	447,737
Adjusted EBITDA	(5,963)	11,427	1,645	51,234
Depreciation, depletion and amortization	19,422	42,203	41,751	90,930
Amortization of acquired sales contracts, net	(75)	(883)	(862)	(2,988)
Capital expenditures	6,740	7,948	10,369	11,333
Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	41,623	77,684	72,989	140,044
Adjusted EBITDA	595	7,456	(2,732)	9,147
Depreciation, depletion and amortization	8,110	10,834	16,043	20,889
Amortization of acquired sales contracts, net	0	0	0	0
Capital expenditures	949	1,668	2,910	4,310
Intersegment Eliminations [Member] | Corporate, Other and Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0
Adjusted EBITDA	(18,924)	(30,209)	(40,241)	(61,997)
Depreciation, depletion and amortization	782	1,624	1,459	3,355
Amortization of acquired sales contracts, net	0	0	0	0
Capital expenditures	$ 60,033	$ 62,440	$ 60,359	$ 62,324