Fair Value Disclosure (Narrative) (Details) - USD ($)	3 Months Ended			12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, at cost				$ 274,422,000	$ 262,661,000
Asset impairment charge	$ 17,400,000	$ 7,500,000
Long-term debt fair value				$ 126,100,000	$ 159,800,000
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				55.80%	56.80%
Coal Lands and Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, at cost				$ 49,331,000	$ 55,623,000
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				48,636,000	54,928,000
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
Reed Minerals | NACoal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset impairment charge	17,400,000		$ 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	$ 5,000,000				$ 0