Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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-Section 50
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- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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Derivatives (Effects of Derivatives on Measures of Financial Performance) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Oct. 01, 2016	Dec. 31, 2017	Dec. 31, 2015
Successor \| Coal
Derivative Instruments, Gain (Loss) [Line Items]
Coal — unrealized	$ (408)		$ (4,648)
Coal — realized	116		0
Successor \| Heating oil -- diesel purchases
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)	827		(1,057)
Successor \| Natural gas
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)	(91)		(774)
Successor \| Foreign currency
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)	(9)		0
Successor \| Coal contract \| Derivatives Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion)	0		(1,185)
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)	0		0
Predecessor \| Coal
Derivative Instruments, Gain (Loss) [Line Items]
Coal — unrealized		$ (1,662)		$ (3,883)
Coal — realized		(476)		3,236
Predecessor \| Heating oil -- diesel purchases
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)		826		(8,294)
Predecessor \| Natural gas
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)		(463)		878
Predecessor \| Foreign currency
Derivative Instruments, Gain (Loss) [Line Items]
Realized Gains (Losses)		(451)		(867)
Predecessor \| Coal contract \| Derivatives Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion)		(136)		6,098
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)		397		9,575
Short \| Successor \| Coal contract \| Derivatives Designated as Hedging Instruments \| Sales Revenue, net
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion)	0		(2,127)
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)	0		0
Short \| Predecessor \| Coal contract \| Derivatives Designated as Hedging Instruments \| Sales Revenue, net
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion)		(672)		12,816
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)		1,634		18,635
Long \| Successor \| Coal contract \| Derivatives Designated as Hedging Instruments \| Cost of Sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion)	0		942
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)	$ 0		$ 0
Long \| Predecessor \| Coal contract \| Derivatives Designated as Hedging Instruments \| Cost of Sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income (Effective Portion)		536		(6,718)
Gains (Losses) Reclassified from Other Comprehensive Income into Income (Effective Portion)		$ (1,237)		$ (9,060)