Business Combination, Tons of Coal Sold from Reserves Covered in Earn-out Period for Earn-out Calculation

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Fair Value Measurement, Valuation Technique Weighting, Percentage

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Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Estimate Increase (Decrease)

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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The amount of identifiable intangible assets recognized as of the acquisition date.

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-Name Accounting Standards Codification

-Topic 805

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Amount recognized for assets, including goodwill, in excess of (less than) the aggregate liabilities assumed.

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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The charge against earnings resulting from the aggregate write down of tangible assets from their carrying value to their fair value.

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Fair Value Disclosure (Narrative) (Details) (USD $)	12 Months Ended			3 Months Ended
Fair Value Disclosure (Narrative) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Aug. 31, 2012 T
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	$ 0	$ 1,581,000	$ 4,000,000	$ 0
Change in estimate, decrease	1,614,000	2,400,000
Reed Minerals goodwill impairment charge	0us-gaap_GoodwillImpairmentLoss	3,973,000us-gaap_GoodwillImpairmentLoss	0us-gaap_GoodwillImpairmentLoss
Property, plant and equipment, at cost	282,303,000us-gaap_PropertyPlantAndEquipmentGross	342,688,000us-gaap_PropertyPlantAndEquipmentGross		282,303,000us-gaap_PropertyPlantAndEquipmentGross
Long-term debt fair value	236,300,000us-gaap_LongTermDebtFairValue	170,700,000us-gaap_LongTermDebtFairValue		236,300,000us-gaap_LongTermDebtFairValue
Reed Minerals
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchase price					70,900,000
Tons of coal sold from reserves covered in earn-out period for earn-out calculation					15,000,000.0
Reed Minerals \| Market approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Valuation technique weighting	25.00%			25.00%
Reed Minerals \| Income approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Valuation technique weighting	75.00%			75.00%
KC
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tangible asset impairment charges	900,000	1,100,000	700,000
Reed Minerals
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Reed Minerals goodwill impairment charge				4,000,000
HBB \| Accounts receivable \| Credit concentration risk \| Five Largest Customers
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Revenue from major customer, percentage	53.30%	53.50%
Coal Lands and Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, at cost	54,923,000	83,962,000		54,923,000
Coal Lands and Real Estate \| NACoal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, at cost	54,228,000	83,736,000		54,228,000
Coal Lands and Real Estate \| HBB
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, at cost	226,000	226,000		226,000
Reed Minerals \| NACoal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Reed Minerals long-lived asset impairment charge				105,100,000
Reed Minerals \| Coal Lands and Real Estate \| NACoal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, at cost	7,200,000			7,200,000
Reed Minerals \| Plant and Equipment \| NACoal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, at cost	37,100,000			37,100,000
Reed Minerals \| Coal Supply Agreement \| NACoal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross Carrying Amount	$ 0			$ 0