Segment Information (Reconciliation Statement Of Segment Income from Operations To Consolidated Income Before Income Taxes) (Details) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
	Mar. 07, 2017	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Asset impairment and mine closure costs				$ (43,700)	$ (85,500)
Net loss resulting from early retirement of debt and debt restructuring	$ 0
Successor
Segment Reporting Information [Line Items]
Adjusted EBITDAR		$ 104,270				$ 320,136
Depreciation, depletion and amortization		(31,914)				(94,536)
Accretion on asset retirement obligations		(7,580)				(22,826)
Amortization of sales contracts, net		(13,861)				(42,903)
Asset impairment and mine closure costs		0				0
Gain on sale of Lone Mountain Processing, Inc.		21,574				21,574
Interest expense, net		(5,252)				(19,311)
Net loss resulting from early retirement of debt and debt restructuring		(486)				(2,547)
Reorganization items, net		(43)				(2,892)
Income (loss) before income taxes		$ 66,708				$ 156,695
Predecessor
Segment Reporting Information [Line Items]
Adjusted EBITDAR			$ 89,333				$ 87,303
Depreciation, depletion and amortization			(69,423)				(191,581)
Accretion on asset retirement obligations			(7,965)				(24,321)
Amortization of sales contracts, net			(104)				728
Asset impairment and mine closure costs			(46)				(129,267)
Gain on sale of Lone Mountain Processing, Inc.			0				0
Interest expense, net			(45,582)				(133,235)
Net loss resulting from early retirement of debt and debt restructuring			0				(2,213)
Reorganization items, net			(20,904)				(46,050)
Income (loss) before income taxes			$ (54,691)				$ (438,636)