Current and Long-Term Financing (Debt Schedule) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Total outstanding borrowings	$ 117,917	$ 157,513
Total debt outstanding	134,753	169,982
Current portion of borrowings outstanding	14,458	9,869
Long-term portion of borrowings outstanding	120,295	160,113
Total available borrowings, net of limitations, under revolving credit agreements	357,433	353,684
Unused revolving credit agreements	239,516	196,171
NACoal
Debt Instrument [Line Items]
Total outstanding borrowings	80,000	100,000
Capital lease obligations and other term loans:	16,039	11,617
Current portion of borrowings outstanding	1,744	1,504
Long-term portion of borrowings outstanding	94,295	110,113
Total available borrowings, net of limitations, under revolving credit agreements	223,933	223,795
Unused revolving credit agreements	$ 143,933	$ 123,795
Weighted average stated interest rate on total borrowings	2.90%	2.40%
Weighted average effective interest rate on total borrowings (including interest rate swap agreements)	3.40%	3.30%
HBB
Debt Instrument [Line Items]
Total outstanding borrowings	$ 37,917	$ 57,513
Other debt	797	852
Current portion of borrowings outstanding	12,714	8,365
Long-term portion of borrowings outstanding	26,000	50,000
Total available borrowings, net of limitations, under revolving credit agreements	112,975	111,590
Unused revolving credit agreements	$ 75,058	$ 54,077
Weighted average stated interest rate on total borrowings	2.30%	2.30%
Weighted average effective interest rate on total borrowings (including interest rate swap agreements)	2.70%	2.70%
KC
Debt Instrument [Line Items]
Total available borrowings, net of limitations, under revolving credit agreements	$ 20,525	$ 18,299
Unused revolving credit agreements	$ 20,525	$ 18,299