Debt and Financing Arrangements (Narrative) (Details) - USD ($)				3 Months Ended		9 Months Ended
	Sep. 25, 2017	Apr. 27, 2017	Mar. 07, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Line of Credit Facility [Line Items]
Net loss resulting from early retirement of debt and debt restructuring			$ 0
Fair value of derivative assets				$ 45,861,000		$ 45,861,000		$ 74,155,000
Debt restructuring costs						2,400,000	$ 2,200,000
Interest Rate Swap | Other Noncurrent Assets
Line of Credit Facility [Line Items]
Fair value of derivative assets				200,000		200,000
New Term Loan Debt Facility | Senior Notes
Line of Credit Facility [Line Items]
Debt instrument, face amount	$ 300,000,000
Call premium rate	1.00%
Net cash proceeds of from debt issuances and other non-ordinary sales or dispositions (percent)			100.00%
Default to indebtedness			$ 50,000,000
Default to surety, reclamation or similar bond			50,000,000
Default to uninsured judgment			50,000,000
Uninsured losses or proceedings against			50,000,000
Debt financing costs	$ 837,000
New Term Loan Debt Facility | Senior Notes | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	3.25%
Previous First Lien Debt Facility | Senior Notes
Line of Credit Facility [Line Items]
Debt restructuring costs						1,300,000
Successor
Line of Credit Facility [Line Items]
Net loss resulting from early retirement of debt and debt restructuring				$ (486,000)		(2,547,000)
Debt financing costs						10,043,000
Debt restructuring costs						2,360,000
Successor | New Term Loan Debt Facility | Senior Notes
Line of Credit Facility [Line Items]
Debt financing costs			7,100,000
Predecessor
Line of Credit Facility [Line Items]
Net loss resulting from early retirement of debt and debt restructuring					$ 0		(2,213,000)
Debt financing costs							20,181,000
Debt restructuring costs							2,213,000
Predecessor | Unsecured Debt
Line of Credit Facility [Line Items]
Interest expense, debt					$ 101,500,000		300,900,000
Predecessor | Superpriority Debtor-in Possession Credit Agreement | Line of Credit
Line of Credit Facility [Line Items]
Debt financing costs							$ 20,200,000
New Term Loan Debt Facility | Senior Notes
Line of Credit Facility [Line Items]
Debt instrument, face amount			$ 300,000,000
Percentage of face amount			99.50%
Quarterly amortization payments			$ 750,000
Amount of voting equity interests of domestic subsidiaries guaranteed (percent)			100.00%
Amount of voting equity interests of foreign owned subsidiaries guaranteed (percent)			65.00%
New Term Loan Debt Facility | Senior Notes | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)			4.00%	3.25%
New Term Loan Debt Facility | Senior Notes | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	2.25%		3.00%
New Term Loan Debt Facility | Minimum | Senior Notes | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)	1.00%		1.00%
Line of Credit | Secured Debt
Line of Credit Facility [Line Items]
Letters of credit outstanding				$ 89,300,000		89,300,000
Current borrowing capacity				102,300,000		102,300,000
Cash collateral for borrowed securities				0		0
Line of Credit | Successor | Secured Debt
Line of Credit Facility [Line Items]
Debt financing costs						2,100,000
Line of Credit | Regions Bank | Secured Debt
Line of Credit Facility [Line Items]
Debt instrument, face amount		$ 40,000,000
Percentage of coal inventory borrowing base		85.00%
Percentage of parts and supplies inventory borrowing base		85.00%
Percentage of clause borrowing base		35.00%
Percent of eligible cash		100.00%
Covenant amount		$ 250,000,000
Covenant minimum amount		175,000,000
Letters of credit outstanding				28,900,000		28,900,000
Maximum borrowing capacity				$ 200,000,000		$ 200,000,000
Current borrowing capacity		$ 160,000,000
Line of Credit | Regions Bank | Minimum | Secured Debt | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)		2.25%
Line of Credit | Regions Bank | Minimum | Secured Debt | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)		1.25%
Line of Credit | Regions Bank | Maximum | Secured Debt | LIBOR
Line of Credit Facility [Line Items]
Percentage of clause borrowing base		2.50%
Line of Credit | Regions Bank | Maximum | Secured Debt | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate (percent)		1.50%