Segment Information (Schedule Of Operating Segment Results) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 428,106	$ 677,005
Adjusted EBITDA	(10,026)	81,772
Depreciation, depletion and amortization	63,699	104,874
Amortization of acquired sales contracts, net	(833)	(3,390)
Capital expenditures	5,926	22,880
Operating Segments [Member] | PRB [Member]
Segment Reporting Information [Line Items]
Revenues	223,122	391,206
Adjusted EBITDA	7,010	72,062
Depreciation, depletion and amortization	32,760	44,361
Amortization of acquired sales contracts, net	(46)	(1,285)
Capital expenditures	10	16,969
Operating Segments [Member] | APP [Member]
Segment Reporting Information [Line Items]
Revenues	173,618	223,439
Adjusted EBITDA	7,607	39,807
Depreciation, depletion and amortization	22,329	50,832
Amortization of acquired sales contracts, net	(787)	(2,105)
Capital expenditures	3,630	3,385
Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	31,366	62,360
Adjusted EBITDA	(3,328)	1,691
Depreciation, depletion and amortization	7,932	10,055
Amortization of acquired sales contracts, net	0	0
Capital expenditures	1,961	2,642
Intersegment Eliminations [Member] | Corporate, Other and Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0	0
Adjusted EBITDA	(21,315)	(31,788)
Depreciation, depletion and amortization	678	(374)
Amortization of acquired sales contracts, net	0	0
Capital expenditures	$ 325	$ (116)