Segment Information (Schedule Of Operating Segment Results) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Segment	Jun. 30, 2016 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | Segment			2
Successor
Segment Reporting Information [Line Items]
Revenues	$ 549,866		$ 1,150,841
Adjusted EBITDAR	95,368		215,866
Depreciation, depletion and amortization	30,701		62,622
Accretion on asset retirement obligations	7,623		15,246
Capital expenditures	10,972		16,922
Successor | Operating Segments | PRB
Segment Reporting Information [Line Items]
Revenues	230,579		504,007
Adjusted EBITDAR	31,789		79,794
Depreciation, depletion and amortization	8,574		18,085
Accretion on asset retirement obligations	5,040		10,080
Capital expenditures	822		950
Successor | Operating Segments | MET
Segment Reporting Information [Line Items]
Revenues	227,649		453,232
Adjusted EBITDAR	62,552		130,862
Depreciation, depletion and amortization	18,385		37,149
Accretion on asset retirement obligations	528		1,057
Capital expenditures	6,825		11,436
Successor | Operating Segments | Other Thermal
Segment Reporting Information [Line Items]
Revenues	91,639		193,545
Adjusted EBITDAR	26,910		54,152
Depreciation, depletion and amortization	3,285		6,485
Accretion on asset retirement obligations	540		1,080
Capital expenditures	1,899		2,640
Successor | Corporate, Other and Eliminations
Segment Reporting Information [Line Items]
Revenues	(1)		57
Adjusted EBITDAR	(25,883)		(48,942)
Depreciation, depletion and amortization	457		903
Accretion on asset retirement obligations	1,515		3,029
Capital expenditures	$ 1,426		$ 1,896
Predecessor
Segment Reporting Information [Line Items]
Revenues		$ 420,298		$ 848,404
Adjusted EBITDAR		(310)		(2,030)
Depreciation, depletion and amortization		58,459		122,158
Accretion on asset retirement obligations		8,050		16,356
Capital expenditures		68,211		74,137
Predecessor | Operating Segments | PRB
Segment Reporting Information [Line Items]
Revenues		207,735		430,857
Adjusted EBITDAR		21,578		34,306
Depreciation, depletion and amortization		30,145		62,905
Accretion on asset retirement obligations		5,647		11,293
Capital expenditures		489		499
Predecessor | Operating Segments | MET
Segment Reporting Information [Line Items]
Revenues		147,499		284,083
Adjusted EBITDAR		(3,593)		2,759
Depreciation, depletion and amortization		17,330		36,675
Accretion on asset retirement obligations		588		1,177
Capital expenditures		6,726		10,330
Predecessor | Operating Segments | Other Thermal
Segment Reporting Information [Line Items]
Revenues		60,032		116,164
Adjusted EBITDAR		(408)		2,743
Depreciation, depletion and amortization		9,907		19,798
Accretion on asset retirement obligations		663		1,325
Capital expenditures		949		2,895
Predecessor | Corporate, Other and Eliminations
Segment Reporting Information [Line Items]
Revenues		5,032		17,300
Adjusted EBITDAR		(17,887)		(41,838)
Depreciation, depletion and amortization		1,077		2,780
Accretion on asset retirement obligations		1,152		2,561
Capital expenditures		$ 60,047		$ 60,413