Income Taxes (Textual) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended	3 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Income tax payments	$ 10.2us-gaap_IncomeTaxesPaid	$ 10.8us-gaap_IncomeTaxesPaid	$ 20.3us-gaap_IncomeTaxesPaid
Income tax refunds	0.9us-gaap_ProceedsFromIncomeTaxRefunds	1.2us-gaap_ProceedsFromIncomeTaxRefunds	0.8us-gaap_ProceedsFromIncomeTaxRefunds
Net (benefit) expense in interest and penalties related to uncertain tax positions	(0.9)	0.4
Interest and penalties accrued	0.5	1.4		0.5
NACoal \| Reed Minerals
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reed Minerals long-lived asset impairment charge				$ 105.1

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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The amount of cash received during the period as refunds for the overpayment of taxes.

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Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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Amount of expense for penalties related to a tax position claimed or expected to be claimed in the tax return.

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