Current and Long-Term Financing (Narrative) (Details)	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Line of Credit Facility [Line Items]
Interest paid	$ 6,500,000	$ 7,400,000	$ 5,300,000
Interest capitalized	(100,000)	(300,000)
Line of credit facility, amount outstanding	157,513,000	232,845,000
Line of credit facility, remaining borrowing capacity	196,171,000	125,851,000
Line of credit facility, current borrowing capacity	353,684,000	358,696,000
NACoal
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	225,000,000
Line of credit facility, amount outstanding	100,000,000	180,000,000
Line of credit facility, remaining borrowing capacity	123,795,000	$ 43,995,000
Amount of letters of credit outstanding	$ 1,200,000
Line of credit facility, unused capacity, commitment fee percentage	0.35%
Weighted average interest rate	3.39%
Minimum interest coverage ratio	4.00
Line of credit facility, availability required to pay dividends	$ 15,000,000
Interest rate at period end	3.30%	3.10%
Line of credit facility, current borrowing capacity	$ 223,795,000	$ 223,995,000
Deferred debt issuance fees and expenses	0	0	1,200,000
NACoal | Note Payable to Coteau
Line of Credit Facility [Line Items]
Debt instrument, amount outstanding	$ 1,400,000
Interest rate at period end	0.55%
NACoal | Maximum
Line of Credit Facility [Line Items]
Maximum EBITDA ratio	3.50
NACoal | Minimum
Line of Credit Facility [Line Items]
Maximum EBITDA ratio	3.00
NACoal | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
NACoal | LIBOR Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
HBB
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 115,000,000
Line of credit facility, amount outstanding	57,513,000	52,845,000
Line of credit facility, remaining borrowing capacity	$ 54,077,000	$ 59,260,000
Line of credit facility, unused capacity, commitment fee percentage	0.25%
Weighted average interest rate	2.72%
Interest rate at period end	2.70%	2.50%
Assets held as collateral	$ 253,900,000
Line of credit facility, current borrowing capacity	111,590,000	$ 112,105,000
Line of credit facility, minimum excess availability	25,000,000
Deferred debt issuance fees and expenses	$ 0	200,000	0
HBB | Base Rate | US Dollar
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
HBB | Base Rate | Canadian Dollar
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
HBB | LIBOR Rate | US Dollar
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
HBB | LIBOR Rate | Canadian Dollar
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
KC
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 25,000,000
Line of credit facility, amount outstanding	0	0
Line of credit facility, remaining borrowing capacity	$ 18,299,000	22,596,000
Line of credit facility, unused capacity, commitment fee percentage	0.32%
Assets held as collateral	$ 53,400,000
Line of credit facility, current borrowing capacity	18,299,000	22,596,000
Deferred debt issuance fees and expenses	0	$ 100,000	$ 0
Dividend restriction from closing date including minimum fixed charge coverage ratio	$ 6,000,000.0
Dividend restriction period following closing date of credit facility	12 months
Dividend restriction credit facility excess availability requirement	$ 7,500,000.0
Minimum fixed charge coverage ratio	1.1
Dividend restriction from closing date	$ 2,000,000.0
Dividend restriction credit facility excess availability requirement as defined within the agreement	$ 15,000,000.0
KC | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
KC | LIBOR Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%