Fair Value Disclosure (Narrative) (Details)	3 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Aug. 31, 2012 T
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in estimate, decrease				$ 1,600,000
Contingent consideration		$ 0	$ 0	0
Reed Minerals long-lived asset impairment charge	$ 7,500,000
Property, plant and equipment, at cost		282,303,000	262,661,000	282,303,000
Centennial goodwill impairment charge			0	0	$ 3,973,000
Long-term debt fair value		236,300,000	$ 159,800,000	236,300,000
Reed Minerals
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tons of coal sold from reserves covered in earn-out period for earn-out calculation | T						15,000,000.0
Reed Minerals | Market approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Valuation technique weighting					25.00%
Reed Minerals | Income approach
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Valuation technique weighting					75.00%
KC
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Tangible asset impairment charges				$ 900,000	$ 1,100,000
Reed Minerals
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Centennial goodwill impairment charge					$ 4,000,000
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			56.80%	53.30%
Coal Lands and Real Estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, at cost		54,923,000	$ 55,623,000	$ 54,923,000
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		54,228,000	54,928,000	54,228,000
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	226,000
Reed Minerals | NACoal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Reed Minerals long-lived asset impairment charge		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		7,200,000		7,200,000
Reed Minerals | Plant and Equipment | NACoal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, plant and equipment, at cost		37,100,000		37,100,000
Reed Minerals | Coal Supply Agreement | NACoal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross Carrying Amount		$ 0		$ 0