Other Transactions (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset impairment		$ 17.4	$ 7.5
Severance and other employee benefit costs					$ 0.6
NACoal
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Legal matter resolution	$ 3.3
NACoal | Land
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of property						$ 2.2
NACoal | Assets Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of property						3.5
NACoal | Reed Minerals
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset impairment		$ 17.4		$ 105.1
HBB | Weston Products, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Preliminary purchase price						25.4
Cash paid at closing						25.0
Net working capital and EBITDA adjustment						$ 0.4