Quarterly Results of Operations (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenues	$ 318.2	$ 210.1	$ 171.4	$ 173.7	$ 273.9	$ 194.6	$ 163.0	$ 158.9	$ 873.4	$ 790.4	$ 885.6
Gross profit	84.8	52.3	43.2	45.6	80.3	48.5	40.0	40.8	647.5	580.8	639.2
Earnings of unconsolidated mines	11.1	11.5	10.6	12.0	12.8	11.1	9.5	12.1	45.2	45.5	43.4
Operating profit (loss)	37.0	14.8	7.7	8.0	42.3	13.3	3.6	4.9	67.5	64.1	94.2
Income from continuing operations	23.7	10.2	3.5	4.8	29.9	8.2	1.4	40.0	42.2	79.5	47.1
Discontinued operation, net of tax	0	27.8	18.3	20.4	24.5	17.5	17.8	22.8	66.5	82.6	32.4
Net Income	23.7	38.0	21.8	25.2	54.4	25.7	19.2	62.8	108.7	162.1	79.5
Basic Earnings per Share:
Continuing operations (in dollars per share)	$ 2.83	$ 1.22	$ 0.42	$ 0.57	$ 3.56	$ 0.98	$ 0.17	$ 4.78	$ 5.04	$ 9.49	$ 5.66
Discontinued operations (in dollars per share)	$ 0.00	$ 3.31	$ 2.18	$ 2.44	$ 2.92	$ 2.08	$ 2.12	$ 2.73	$ 7.93	$ 9.85	$ 3.89
Basic Earnings per Share (in dollars per share)	$ 2.83	$ 4.53	$ 2.60	$ 3.01	$ 6.48	$ 3.06	$ 2.29	$ 7.51	$ 12.97	$ 19.34	$ 9.55
Diluted Earnings per Share:
Continuing operations (in dollars per share)	$ 2.81	$ 1.21	$ 0.42	$ 0.57	$ 3.56	$ 0.97	$ 0.17	$ 4.76	$ 5.02	$ 9.46	$ 5.65
Discontinued operations (in dollars per share)	$ 0.00	$ 3.31	$ 2.18	$ 2.43	$ 2.91	$ 2.08	$ 2.11	$ 2.72	$ 7.90	$ 9.82	$ 3.88
Diluted Earnings per Share (in dollars per share)	$ 2.81	$ 4.52	$ 2.60	$ 3.00	$ 6.47	$ 3.05	$ 2.28	$ 7.48	$ 12.92	$ 19.28	$ 9.53
NACoal
Segment Reporting Information [Line Items]
Revenues	50.9	38.0	19.2	24.3	23.5	21.0	19.4	17.9	132.4	81.8	156.8
Operating profit (loss)	13.5	8.6	9.2	11.9	13.4	7.0	5.3	9.5	43.2	35.2	53.3
Income from continuing operations	8.3	8.2	7.1	9.2					32.8	29.4	39.6
Net Income					11.9	5.8	4.6	7.1
HBB
Segment Reporting Information [Line Items]
Revenues	181.2	124.8	110.7	104.9	161.4	126.7	104.3	100.6	521.6	493.0	515.7
Operating profit (loss)	19.9	8.7	5.1	2.1	19.0	7.9	3.6	3.3	35.8	33.8	45.9
Income from continuing operations	12.7	5.3	2.2	1.0					21.2	18.4	24.4
Net Income					12.0	4.1	1.3	1.0
KC
Segment Reporting Information [Line Items]
Revenues	88.9	48.2	42.3	45.3	91.4	48.9	40.0	40.9	224.7	221.2	219.6
Operating profit (loss)	7.0	(1.9)	(5.1)	(4.6)	12.8	(0.6)	(4.3)	(5.4)	(4.6)	2.5	5.9
Income from continuing operations	4.1	(1.2)	(3.2)	(2.8)					(3.1)	1.1	3.5
Net Income					7.6	(0.5)	(2.7)	(3.3)
NACCO and Other
Segment Reporting Information [Line Items]
Operating profit (loss)	(3.4)	(0.6)	(1.5)	(1.5)	(2.8)	(0.9)	(1.1)	(2.5)	(7.0)	(7.3)	(10.8)
Income from continuing operations	(4.4)	(1.1)	(1.7)	(1.4)					(8.6)	30.7	(20.4)
Net Income					(2.3)	(0.7)	(1.0)	34.7
Eliminations
Segment Reporting Information [Line Items]
Revenues	(2.8)	(0.9)	(0.8)	(0.8)	(2.4)	(2.0)	(0.7)	(0.5)	(5.3)	(5.6)	(6.5)
Operating profit (loss)	0	0	0	0.1	(0.1)	(0.1)	0.1	0	0.1	(0.1)	(0.1)
Income from continuing operations	3.0	(1.0)	(0.9)	(1.2)					(0.1)	(0.1)	0
Net Income					0.7	(0.5)	(0.8)	0.5
Reed Minerals
Segment Reporting Information [Line Items]
Revenues	21.6	7.7
Reed Minerals | NACoal
Segment Reporting Information [Line Items]
Operating profit (loss)	$ 1.5	$ 0