Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets, Net [Abstract]
Net Balance	$ 52,959	$ 56,843
Amortization of intangible assets	3,884	3,987	$ 3,300
HBB
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	10,100
Accumulated Amortization	(2,818)
Net Balance	7,282
Expected annual amortization expense, 2017	1,400
Expected annual amortization expense, 2018	1,400
Expected annual amortization expense, 2019	1,400
Expected annual amortization expense, 2020	1,200
Expected annual amortization expense, 2021	$ 200
Coal supply agreement amortization period	9 years
HBB | Coal Supply Agreement
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount		10,100
Accumulated Amortization		(1,437)
Net Balance		8,663
HBB | Customer Relationships
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	$ 5,760	5,760
Accumulated Amortization	(1,960)	(1,000)
Net Balance	3,800	4,760
HBB | Trademarks
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	3,100	3,100
Accumulated Amortization	(408)	(208)
Net Balance	2,692	2,892
HBB | Other Intangibles
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	1,240	1,240
Accumulated Amortization	(450)	(229)
Net Balance	790	1,011
NACoal
Finite-Lived Intangible Assets, Net [Abstract]
Expected annual amortization expense, 2017	2,800
Expected annual amortization expense, 2018	2,900
Expected annual amortization expense, 2019	2,900
Expected annual amortization expense, 2020	2,900
Expected annual amortization expense, 2021	$ 2,900
Coal supply agreement amortization period	30 years
NACoal | Coal Supply Agreement
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	$ 84,200	84,200
Accumulated Amortization	(38,523)	(36,020)
Net Balance	$ 45,677	$ 48,180