Current and Long-Term Financing (Debt Schedule) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Total outstanding borrowings:	$ 232,845us-gaap_LineOfCredit	$ 159,907us-gaap_LineOfCredit
Private Placement Notes — NACoal	236,260us-gaap_LongTermDebt
Total debt outstanding	247,898us-gaap_DebtAndCapitalLeaseObligations	183,750us-gaap_DebtAndCapitalLeaseObligations
Current portion of borrowings outstanding:	56,467	31,319
Long-term portion of borrowings outstanding:	191,431us-gaap_LongTermDebtNoncurrent	152,431us-gaap_LongTermDebtNoncurrent
Total available borrowings, net of limitations, under revolving credit agreements:	358,696	362,520
Unused revolving credit agreements:	125,851	202,613
NACoal
Debt Instrument [Line Items]
Total outstanding borrowings:	180,000	140,000
Capital lease obligations and other term loans:	14,445	17,414
Current portion of borrowings outstanding:	56,467	29,859
Long-term portion of borrowings outstanding:	137,978	133,984
Total available borrowings, net of limitations, under revolving credit agreements:	223,995	223,936
Unused revolving credit agreements:	43,995	83,936
Weighted average stated interest rate on total borrowings:	2.50%	2.30%
Interest rate at period end	3.10%	3.00%
NACoal \| Private Placement Notes
Debt Instrument [Line Items]
Private Placement Notes — NACoal	0	6,429
HBB
Debt Instrument [Line Items]
Total outstanding borrowings:	52,845	18,447
Other borrowings	608	0
Long-term portion of borrowings outstanding:	53,453	18,447
Total available borrowings, net of limitations, under revolving credit agreements:	112,105	111,584
Unused revolving credit agreements:	59,260	93,137
Weighted average stated interest rate on total borrowings:	2.00%	3.20%
Interest rate at period end	2.50%	3.20%
KC
Debt Instrument [Line Items]
Total outstanding borrowings:	0	1,460
Current portion of borrowings outstanding:	0	1,460
Total available borrowings, net of limitations, under revolving credit agreements:	22,596	27,000
Unused revolving credit agreements:	$ 22,596	$ 25,540
Weighted average stated interest rate on total borrowings:		4.30%

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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