Derivatives (Disclosure of Fair Value of Derivatives) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Predecessor [Member]
Derivative [Line Items]
Derivative Assets		$ 116,080
Derivative Liabilities		(107,028)
Effect of counterparty netting in derivative assets		(107,028)
Effect of counterparty netting in derivative liabilities		107,028
Net derivative assets as classified in the balance sheet		9,052
Net derivative liabilities as classified in the balance sheet		0
Net derivatives as classified in the balance sheet		9,052
Predecessor [Member] \| Designated as Hedging Instrument [Member] \| Coal [Member]
Derivative [Line Items]
Derivative Assets		4
Derivative Liabilities		(20)
Predecessor [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Assets		116,076
Derivative Liabilities		(107,008)
Predecessor [Member] \| Not Designated as Hedging Instrument [Member] \| Heating Oil-Diesel Purchases [Member]
Derivative [Line Items]
Derivative Assets		1,017
Predecessor [Member] \| Not Designated as Hedging Instrument [Member] \| Coal Held for Trading Purposes [Member]
Derivative [Line Items]
Derivative Assets		110,653
Derivative Liabilities		(104,814)
Predecessor [Member] \| Not Designated as Hedging Instrument [Member] \| Coal [Member]
Derivative [Line Items]
Derivative Assets		3,912
Derivative Liabilities		(1,947)
Predecessor [Member] \| Not Designated as Hedging Instrument [Member] \| Natural Gas [Member]
Derivative [Line Items]
Derivative Assets		494
Derivative Liabilities		$ (247)
Successor [Member]
Derivative [Line Items]
Derivative Assets	$ 74,155
Derivative Liabilities	(69,348)
Effect of counterparty netting in derivative assets	(69,247)
Effect of counterparty netting in derivative liabilities	69,247
Net derivative assets as classified in the balance sheet	4,908
Net derivative liabilities as classified in the balance sheet	(101)
Net derivatives as classified in the balance sheet	4,807
Successor [Member] \| Designated as Hedging Instrument [Member] \| Coal [Member]
Derivative [Line Items]
Derivative Assets	0
Derivative Liabilities	(15)
Successor [Member] \| Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Assets	74,155
Derivative Liabilities	(69,333)
Successor [Member] \| Not Designated as Hedging Instrument [Member] \| Heating Oil-Diesel Purchases [Member]
Derivative [Line Items]
Derivative Assets	4,646
Successor [Member] \| Not Designated as Hedging Instrument [Member] \| Coal Held for Trading Purposes [Member]
Derivative [Line Items]
Derivative Assets	68,948
Derivative Liabilities	(68,740)
Successor [Member] \| Not Designated as Hedging Instrument [Member] \| Coal [Member]
Derivative [Line Items]
Derivative Assets	475
Derivative Liabilities	(580)
Successor [Member] \| Not Designated as Hedging Instrument [Member] \| Natural Gas [Member]
Derivative [Line Items]
Derivative Assets	86
Derivative Liabilities	$ (13)

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities.

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