Derivative Financial Instruments (Details) - Interest rate contract - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
HBB
Derivative [Line Items]
Notional amount of interest rate derivatives	$ 20.0	$ 20.0
Average fixed interest rate of interest rate derivatives	1.40%	1.40%
Remaining term	extending to January 2020
NACoal
Derivative [Line Items]
Notional amount of interest rate derivatives	$ 100.0	$ 100.0
Average fixed interest rate of interest rate derivatives	1.40%	1.40%
Remaining term	extending to May 2018