Current and Long-Term Financing (Debt Schedule) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Total outstanding borrowings:	$ 157,513	$ 232,845
Total debt outstanding	169,982	247,898
Current portion of borrowings outstanding:	9,869	56,467
Long-term portion of borrowings outstanding:	160,113	191,431
Total available borrowings, net of limitations, under revolving credit agreements:	353,684	358,696
Unused revolving credit agreements:	196,171	125,851
NACoal
Debt Instrument [Line Items]
Total outstanding borrowings:	100,000	180,000
Capital lease obligations and other term loans:	11,617	14,445
Current portion of borrowings outstanding:	1,504	56,467
Long-term portion of borrowings outstanding:	110,113	137,978
Total available borrowings, net of limitations, under revolving credit agreements:	223,795	223,995
Unused revolving credit agreements:	$ 123,795	$ 43,995
Weighted average stated interest rate on total borrowings:	2.40%	2.50%
Interest rate at period end	3.30%	3.10%
HBB
Debt Instrument [Line Items]
Total outstanding borrowings:	$ 57,513	$ 52,845
Other borrowings	852	608
Current portion of borrowings outstanding:	8,365	0
Long-term portion of borrowings outstanding:	50,000	53,453
Total available borrowings, net of limitations, under revolving credit agreements:	111,590	112,105
Unused revolving credit agreements:	$ 54,077	$ 59,260
Weighted average stated interest rate on total borrowings:	2.30%	2.00%
Interest rate at period end	2.70%	2.50%
KC
Debt Instrument [Line Items]
Total outstanding borrowings:	$ 0	$ 0
Current portion of borrowings outstanding:	0	0
Total available borrowings, net of limitations, under revolving credit agreements:	18,299	22,596
Unused revolving credit agreements:	$ 18,299	$ 22,596