Segment Information (Reconciliation Statement Of Segment Income from Operations To Consolidated Income Before Income Taxes) (Details) - USD ($)		3 Months Ended			6 Months Ended
	Mar. 07, 2017	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Asset impairment and mine closure costs			$ 43,700,000	$ 85,500,000
Net loss resulting from early retirement of debt and debt restructuring	$ 0
Successor
Segment Reporting Information [Line Items]
Adjusted EBITDAR		$ 95,368,000			$ 215,866,000
Depreciation, depletion and amortization		30,701,000			62,622,000
Accretion on asset retirement obligations		7,623,000			15,246,000
Amortization of sales contracts, net		14,352,000			29,042,000
Asset impairment and mine closure costs		0			0
Interest expense, net		(5,161,000)			(14,059,000)
Net loss resulting from early retirement of debt and debt restructuring		(31,000)			(2,061,000)
Reorganization items, net		(21,000)			(2,849,000)
Income (loss) before income taxes		$ 37,479,000			$ 89,987,000
Predecessor
Segment Reporting Information [Line Items]
Adjusted EBITDAR			(310,000)			$ (2,030,000)
Depreciation, depletion and amortization			58,459,000			122,158,000
Accretion on asset retirement obligations			8,050,000			16,356,000
Amortization of sales contracts, net			1,000			(832,000)
Asset impairment and mine closure costs			43,701,000			129,221,000
Interest expense, net			(44,340,000)			(87,653,000)
Net loss resulting from early retirement of debt and debt restructuring			0			(2,213,000)
Reorganization items, net			(21,271,000)			(25,146,000)
Income (loss) before income taxes			$ (176,132,000)			$ (383,945,000)