Correction of Errors in Previously Reported Financial Statements (Details 1) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2011	Mar. 31, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Continuing Operations
Net sales	$ 257.4	$ 235.6	$ 243.1	$ 218.6	$ 493.0	$ 461.7	$ 943.8	$ 826.2	$ 688.5
Cost of sales	182.8	171.0	181.1	160.2	353.8	341.3	690.9	612.0	503.0
Gross profit	74.6	64.6	62.0	58.4	139.2	120.4	252.9	214.2	185.2
Selling, general and administrative expenses	43.6	43.3	41.0	39.1	86.9	80.1	165.8	145.0	135.2
Operating profit	31.0	21.3	21.0	19.3	52.3	40.3	87.1	69.2	50.0
Other income (expense):
Interest expense, net	(2.7)	(2.7)	(2.7)	(2.6)	(5.4)	(5.3)	(11.3)	(9.6)	(12.0)
Other, net	(0.5)	(2.2)	0.5	(0.4)	(2.7)	0.1	0.2	1.3	(0.3)
Total other income (expense), net	(3.2)	(4.9)	(2.2)	(3.0)	(8.1)	(5.2)	(11.1)	(8.3)	(12.3)
Income before income taxes and income (loss) from affiliates and joint ventures	27.8	16.4	18.8	16.3	44.2	35.1	76.0	60.9	37.7
Income tax expense (benefit)	7.6	4.3	5.7	3.9	11.9	9.6	20.5	20.8	4.9
Income before income (loss) from affiliates and joint ventures	20.2	12.1	13.1	12.4	32.3	25.5	55.5	40.1	32.8
Income (loss) from affiliates and joint ventures	1.1	1.2	(0.1)	1.0	2.3	0.9	5.3	(11.1)
Income (loss) from continuing operations	21.3	13.3	13.0	13.4	34.6	26.4	60.8	29.0	32.8
Discontinued Operations
Income (loss) on discontinued operations			0.2	(0.1)		0.1	(1.2)	(0.9)	0.3
Net income (loss)	21.3	13.3	13.2	13.3	34.6	26.5	59.6	28.1	33.1
Net income (loss) attributable to noncontrolling interests	(0.3)	0.1			(0.2)			(0.8)	(0.1)
Net income attributable to AMCOL shareholders	21.6	13.2	13.2	13.3	34.8	26.5	59.6	28.9	33.2
Weighted average common shares outstanding	32.0	32.0	31.7	31.5	32.0	31.6	31.7	31.2	30.8
Weighted average common and common equivalent shares	32.3	32.3	32.2	32.0	32.3	32.1	32.1	31.5	31.0
Amounts attributable to AMCOL shareholders
Income from continuing operations, net of tax	21.6	13.2	13.0	13.4	34.8	26.4	60.8	29.8	32.9
Discontinued operations, net of tax			0.2	(0.1)		0.1	(1.2)	(0.9)	0.3
Net income	21.6	13.2	13.2	13.3	34.8	26.5	59.6	28.9	33.2
Basic earnings (loss) per share:
Continuing operations	$ 0.67	$ 0.41	$ 0.41	$ 0.42	$ 1.09	$ 0.84	$ 1.92	$ 0.96	$ 1.07
Discontinued operations			$ 0.01				$ (0.04)	$ (0.03)	$ 0.01
Net income	$ 0.67	$ 0.41	$ 0.42	$ 0.42	$ 1.09	$ 0.84	$ 1.88	$ 0.93	$ 1.08
Diluted earnings (loss) per share:
Continuing operations	$ 0.67	$ 0.41	$ 0.40	$ 0.42	$ 1.08	$ 0.83	$ 1.89	$ 0.95	$ 1.06
Discontinued operations			$ 0.01				$ (0.04)	$ (0.03)	$ 0.01
Net income	$ 0.67	$ 0.41	$ 0.41	$ 0.42	$ 1.08	$ 0.83	$ 1.85	$ 0.92	$ 1.07
Previously reported [Member]
Continuing Operations
Net sales		235.8	242.8	217.8		460.6	942.4	841.0	691.9
Cost of sales		170.7	180.7	160.1		340.8	689.5	624.1	505.6
Gross profit		65.1	62.1	57.7		119.8	252.9	216.9	186.3
Selling, general and administrative expenses		43.6	40.3	39.1		79.4	165.2	146.9	133.4
Operating profit		21.5	21.8	18.6		40.4	87.7	70.0	52.9
Other income (expense):
Interest expense, net		(2.7)	(2.8)	(2.7)		(5.5)	(11.5)	(9.7)	(12.2)
Other, net		(2.1)	0.5	(0.4)		0.1	0.2	1.2	(0.9)
Total other income (expense), net		(4.8)	(2.3)	(3.1)		(5.4)	(11.3)	(8.5)	(13.1)
Income before income taxes and income (loss) from affiliates and joint ventures		16.7	19.5	15.5		35.0	76.4	61.5	39.8
Income tax expense (benefit)		4.8	5.9	4.3		10.2	21.8	19.4	5.3
Income before income (loss) from affiliates and joint ventures		11.9	13.6	11.2		24.8	54.6	42.1	34.5
Income (loss) from affiliates and joint ventures		1.2	(0.1)	1.1		1.0	5.5	(11.3)	0.1
Income (loss) from continuing operations		13.1	13.5	12.3		25.8	60.1	30.8	34.8
Discontinued Operations
Income (loss) on discontinued operations		(0.2)	0.2	(0.1)		0.1	(0.9)	(0.9)	0.3
Net income (loss)		12.9	13.7	12.2		25.9	59.2	29.9	34.9
Net income (loss) attributable to noncontrolling interests		0.1					0.1	(0.4)	0.1
Net income attributable to AMCOL shareholders		12.8	13.7	12.2		25.9	59.1	30.3	34.8
Weighted average common shares outstanding		32.0	31.7	31.5		31.6	31.7	31.2	30.8
Weighted average common and common equivalent shares		32.3	32.2	32.0		32.1	32.1	31.5	31.0
Amounts attributable to AMCOL shareholders
Income from continuing operations, net of tax		13.0	13.5	12.3		25.8	60.0	31.2	34.5
Discontinued operations, net of tax		(0.2)	0.2	(0.1)		0.1	(0.9)	(0.9)	0.3
Net income		12.8	13.7	12.2		25.9	59.1	30.3	34.8
Basic earnings (loss) per share:
Continuing operations		$ 0.41	$ 0.42	$ 0.39		$ 0.82	$ 1.89	$ 1.00	$ 1.12
Discontinued operations		$ (0.01)	$ 0.01				$ (0.03)	$ (0.03)	$ 0.01
Net income		$ 0.40	$ 0.43	$ 0.39		$ 0.82	$ 1.86	$ 0.97	$ 1.13
Diluted earnings (loss) per share:
Continuing operations		$ 0.41	$ 0.42	$ 0.38		$ 0.81	$ 1.87	$ 0.99	$ 1.11
Discontinued operations		$ (0.01)	$ 0.01				$ (0.03)	$ (0.03)	$ 0.01
Net income		$ 0.40	$ 0.43	$ 0.38		$ 0.81	$ 1.84	$ 0.96	$ 1.12
Adjustments [Member]
Continuing Operations
Net sales		(0.2)	0.3	0.8		1.1	1.4	(14.8)	(3.7)
Cost of sales		0.3	0.4	0.1		0.5	1.4	(12.1)	(2.6)
Gross profit		(0.5)	(0.1)	0.7		0.6		(2.7)	(1.1)
Selling, general and administrative expenses		(0.3)	0.7			0.7	0.6	(1.9)	1.8
Operating profit		(0.2)	(0.8)	0.7		(0.1)	(0.6)	(0.8)	(2.9)
Other income (expense):
Interest expense, net			0.1	0.1		0.2	0.2	0.1	0.2
Other, net		(0.1)						0.1	0.6
Total other income (expense), net		(0.1)	0.1	0.1		0.2	0.2	0.2	0.8
Income before income taxes and income (loss) from affiliates and joint ventures		(0.3)	(0.7)	0.8		0.1	(0.4)	(0.6)	(2.1)
Income tax expense (benefit)		(0.5)	(0.2)	(0.4)		(0.6)	(1.3)	1.4	(0.4)
Income before income (loss) from affiliates and joint ventures		0.2	(0.5)	1.2		0.7	0.9	(2.0)	(1.7)
Income (loss) from affiliates and joint ventures				(0.1)		(0.1)	(0.2)	0.2	(0.1)
Income (loss) from continuing operations		0.2	(0.5)	1.1		0.6	0.7	(1.8)	(1.8)
Discontinued Operations
Income (loss) on discontinued operations		0.2					(0.3)
Net income (loss)		0.4	(0.5)	1.1		0.6	0.4	(1.8)	(1.8)
Net income (loss) attributable to noncontrolling interests							(0.1)	(0.4)	(0.2)
Net income attributable to AMCOL shareholders		0.4	(0.5)	1.1		0.6	0.5	(1.4)	(1.6)
Weighted average common shares outstanding		32.0	31.7	31.5		31.6	31.7	31.2	30.8
Weighted average common and common equivalent shares		32.3	32.2	32.0		32.1	32.1	31.5	31.0
Amounts attributable to AMCOL shareholders
Income from continuing operations, net of tax		0.2	(0.5)	1.1		0.6	0.8	(1.4)	(1.6)
Discontinued operations, net of tax		0.2					(0.3)
Net income		0.4	(0.5)	1.1		0.6	0.5	(1.4)	(1.6)
Basic earnings (loss) per share:
Continuing operations			$ (0.01)	$ 0.03		$ 0.02	$ 0.03	$ (0.04)	$ (0.05)
Discontinued operations		$ 0.01					$ (0.01)
Net income		$ 0.01	$ (0.01)	$ 0.03		$ 0.02	$ 0.02	$ (0.04)	$ (0.05)
Diluted earnings (loss) per share:
Continuing operations			$ (0.02)	$ 0.04		$ 0.02	$ 0.02	$ (0.04)	$ (0.05)
Discontinued operations		$ 0.01					$ (0.01)
Net income		$ 0.01	$ (0.02)	$ 0.04		$ 0.02	$ 0.01	$ (0.04)	$ (0.05)
Tax [Member] | Adjustments [Member]
Continuing Operations
Net sales
Gross profit
Operating profit
Other income (expense):
Income before income taxes and income (loss) from affiliates and joint ventures
Income tax expense (benefit)		(0.3)		(0.5)		(0.5)	(1.7)	1.2	(0.1)
Income before income (loss) from affiliates and joint ventures		0.3		0.5		0.5	1.7	(1.2)	0.1
Income (loss) from affiliates and joint ventures				(0.1)		(0.1)	(0.2)
Income (loss) from continuing operations		0.3		0.4		0.4	1.5	(1.2)	0.1
Discontinued Operations
Net income (loss)		0.3		0.4		0.4	1.5	(1.2)	0.1
Net income attributable to AMCOL shareholders		0.3		0.4		0.4	1.5	(1.2)	0.1
Other [Member] | Adjustments [Member]
Continuing Operations
Net sales		(0.2)	0.3	0.2		0.5	0.8	(14.2)	(3.7)
Cost of sales		(0.2)		(0.3)		(0.3)	(0.1)	(12.7)	(3.8)
Gross profit			0.3	0.5		0.8	0.9	(1.5)	0.1
Selling, general and administrative expenses		(0.1)						(1.5)	1.5
Operating profit		0.1	0.3	0.5		0.8	0.9	0	(1.4)
Other income (expense):
Interest expense, net		0.1	0.1	0.1		0.2	0.2	0.1	0.2
Other, net								0.1	0.6
Total other income (expense), net		0.1	0.1	0.1		0.2	0.2	0.2	0.8
Income before income taxes and income (loss) from affiliates and joint ventures			0.4	0.6		1.0	1.1	0.2	(0.6)
Income tax expense (benefit)		(0.2)	(0.1)	(0.1)		(0.2)	0.4	0.2
Income before income (loss) from affiliates and joint ventures		0.2	0.5	0.7		1.2	0.7	0	(0.6)
Income (loss) from affiliates and joint ventures								0.2	(0.1)
Income (loss) from continuing operations		0.2	0.5	0.7		1.2	0.7	0.2	0.7
Discontinued Operations
Income (loss) on discontinued operations		0.2					(0.3)
Net income (loss)		0.4	0.5	0.7		1.2	0.4	0.2	0.7
Net income (loss) attributable to noncontrolling interests								(0.4)
Net income attributable to AMCOL shareholders		0.4	0.5	0.7		1.2	0.4	0.6	(0.7)
Spain [Member] | Adjustments [Member]
Continuing Operations
Cost of sales		0.4	0.3	0.3		0.6	1.2	0.6	0.7
Gross profit		(0.4)	(0.3)	(0.3)		(0.6)	(1.2)	(0.6)	(0.7)
Selling, general and administrative expenses		(0.2)					0.1		0.3
Operating profit		(0.2)	(0.3)	(0.3)		(0.6)	(1.3)	(0.6)	(1.0)
Other income (expense):
Income before income taxes and income (loss) from affiliates and joint ventures		(0.2)	(0.3)	(0.3)		(0.6)	(1.3)	(0.6)	(1.0)
Income tax expense (benefit)		0.1					(0.2)		(0.2)
Income before income (loss) from affiliates and joint ventures		(0.3)	(0.3)	(0.3)		(0.6)	(1.1)	(0.6)	(0.8)
Income (loss) from continuing operations		(0.3)	(0.3)	(0.3)		(0.6)	(1.1)	(0.6)	(0.8)
Discontinued Operations
Net income (loss)		(0.3)	(0.3)	(0.3)		(0.6)	(1.1)	(0.6)	(0.8)
Net income attributable to AMCOL shareholders		(0.3)	(0.3)	(0.3)		(0.6)	(1.1)	(0.6)	(0.8)
South Africa [Member] | Adjustments [Member]
Continuing Operations
Cost of sales		0.1	0.1	0.1		0.2	0.3		0.5
Gross profit		(0.1)	(0.1)	(0.1)		(0.2)	(0.3)		(0.5)
Selling, general and administrative expenses								(0.1)	0.1
Operating profit		(0.1)	(0.1)	(0.1)		(0.2)	(0.3)	0.1	(0.6)
Other income (expense):
Income before income taxes and income (loss) from affiliates and joint ventures		(0.1)	(0.1)	(0.1)		(0.2)	(0.3)	0.1	(0.6)
Income tax expense (benefit)		(0.1)	0.1	0.1		0.2	0.3	0.1	(0.1)
Income before income (loss) from affiliates and joint ventures			(0.2)	(0.2)		(0.4)	(0.6)		(0.5)
Income (loss) from continuing operations			(0.2)	(0.2)		(0.4)	(0.6)		(0.5)
Discontinued Operations
Net income (loss)			(0.2)	(0.2)		(0.4)	(0.6)		(0.5)
Net income (loss) attributable to noncontrolling interests							(0.1)		(0.2)
Net income attributable to AMCOL shareholders			(0.2)	(0.2)		(0.4)	(0.5)		(0.3)
Dong Ming [Member] | Adjustments [Member]
Continuing Operations
Net sales
Gross profit
Selling, general and administrative expenses			0.7			0.7	0.7	(0.3)	(0.1)
Operating profit			(0.7)			(0.7)	(0.7)	0.3	0.1
Other income (expense):
Income before income taxes and income (loss) from affiliates and joint ventures			(0.7)			(0.7)	(0.7)	0.3	0.1
Income tax expense (benefit)			(0.2)			(0.2)	(0.2)	0.1	0.1
Income before income (loss) from affiliates and joint ventures			(0.5)			(0.5)	(0.5)	0.2	0.1
Income (loss) from continuing operations			(0.5)			(0.5)	(0.5)	0.2	0.1
Discontinued Operations
Net income (loss)			(0.5)			(0.5)	(0.5)	0.2	0.1
Net income attributable to AMCOL shareholders			(0.5)			(0.5)	(0.5)	0.2	0.1
Malaysia [Member]
Continuing Operations
Gross profit							0.6
Malaysia [Member] | Adjustments [Member]
Continuing Operations
Net sales				0.6		0.6	0.6	(0.6)
Gross profit				0.6		0.6		(0.6)
Selling, general and administrative expenses							(0.2)
Operating profit				0.6		0.6	0.8	(0.6)
Other income (expense):
Income before income taxes and income (loss) from affiliates and joint ventures				0.6		0.6	0.8	(0.6)
Income tax expense (benefit)				0.1		0.1	0.1	(0.2)
Income before income (loss) from affiliates and joint ventures				0.5		0.5	0.7	(0.4)
Income (loss) from continuing operations				0.5		0.5	0.7	(0.4)
Discontinued Operations
Net income (loss)				0.5		0.5	0.7	(0.4)
Net income attributable to AMCOL shareholders				$ 0.5		$ 0.5	$ 0.7	$ (0.4)