Correction of Errors in Previously Reported Financial Statements (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current assets:
Cash and cash equivalents	$ 16.8	$ 16.9	$ 23.7	$ 17.9	$ 21.2	$ 26.8	$ 27.7
Accounts receivable, net	217.2		204.8			190.1
Inventories	146.0		144.8			105.6
Prepaid expenses	19.2		15.7			13.0
Deferred income taxes	4.2		5.9			5.5
Income tax receivable	11.0		6.9			8.5
Other	4.0		6.1			6.2
Total current assets	418.4		407.9			355.7
Property, plant, equipment, and mineral rights and reserves:
Land	13.9		13.9			10.9
Mineral rights	49.8		52.5			65.0
Depreciable assets	507.8		482.6			452.3
Gross property, plant and equipment	571.5		549.0			528.2
Less: accumulated depreciation and depletion	291.4		275.5			256.7
Net property, plant and equipment	280.1		273.5			271.5
Goodwill	69.4		69.5			70.9
Intangible assets, net	35.8		36.6			41.9
Investment in and advances to affiliates and joint ventures	26.8		26.4			20.9
Available-for-sale securities	3.0		3.8			14.2
Deferred income taxes	9.0		8.5			9.2
Other assets	26.5		24.4			23.5
Total noncurrent assets	450.6		442.7			452.1
Total Assets	869.0		850.6			807.8
Current liabilities:
Accounts payable	50.3		56.5			51.4
Accrued income taxes	10.1		2.4			5.1
Accrued liabilities	58.3		57.9			55.2
Total current liabilities	118.7		116.8			111.7
Noncurrent liabilities:
Long-term debt	251.0		260.7			235.7
Pension liabilities	35.2		34.8			21.3
Deferred compensation	9.0		8.9			9.0
Deferred income taxes	12.9		13.5			16.6
Other long-term liabilities	19.3		19.2			18.4
Total noncurrent liabilities	327.4		337.1			301.0
Shareholders' Equity:
Common stock	0.3		0.3			0.3
Additional paid in capital	99.2		94.3			95.1
Retained earnings	339.7		316.4			279.6
Accumulated other comprehensive income (loss)	(18.8)		(15.0)			28.7
Less: Treasury stock	(1.3)		(3.4)			(8.9)
Total AMCOL shareholders' equity	419.1		392.6			394.8
Noncontrolling interest	3.8		4.1			0.3
Total equity	422.9		396.7	410.6		395.1
Total Liabilities and Shareholders' Equity	869.0		850.6			807.8
Previously reported [Member]
Current assets:
Cash and cash equivalents		16.9	23.7	17.9	21.2	27.3	27.7
Accounts receivable, net			206.8			194.0
Inventories			146.6			107.5
Prepaid expenses			15.7			12.6
Deferred income taxes			5.9			5.5
Income tax receivable			6.9			8.5
Other			6.7			6.2
Total current assets			412.3			361.6
Property, plant, equipment, and mineral rights and reserves:
Land			13.9			11.6
Mineral rights			41.9			51.4
Depreciable assets			482.3			454.4
Gross property, plant and equipment			538.1			517.4
Less: accumulated depreciation and depletion			275.5			256.9
Net property, plant and equipment			262.6			260.5
Goodwill			69.5			70.9
Intangible assets, net			36.6			42.6
Investment in and advances to affiliates and joint ventures			26.4			19.0
Available-for-sale securities			3.8			14.2
Deferred income taxes			7.8			7.6
Other assets			23.7			22.7
Total noncurrent assets			430.4			437.5
Total Assets			842.7			799.1
Current liabilities:
Accounts payable			56.4			53.2
Accrued income taxes			2.7			4.1
Accrued liabilities			59.0			55.2
Total current liabilities			118.1			112.5
Noncurrent liabilities:
Long-term debt			260.7			236.2
Pension liabilities			34.8			21.3
Deferred compensation			8.9			8.7
Deferred income taxes			0.8			0.4
Other long-term liabilities			19.2			19.6
Total noncurrent liabilities			324.4			286.2
Shareholders' Equity:
Common stock			0.3			0.3
Additional paid in capital			94.5			95.1
Retained earnings			319.5			283.2
Accumulated other comprehensive income (loss)			(14.9)			28.9
Less: Treasury stock			(3.4)			(8.9)
Total AMCOL shareholders' equity			396.0			398.6
Noncontrolling interest			4.2			1.8
Total equity			400.2			400.4
Total Liabilities and Shareholders' Equity			842.7			799.1
Adjustments [Member]
Current assets:
Cash and cash equivalents						(0.5)
Accounts receivable, net			(2.0)			(3.9)
Inventories			(1.8)			(1.9)
Prepaid expenses						0.4
Other			(0.6)
Total current assets			(4.4)			(5.9)
Property, plant, equipment, and mineral rights and reserves:
Land						(0.7)
Mineral rights			10.6			13.6
Depreciable assets			0.3			(2.1)
Gross property, plant and equipment			10.9			10.8
Less: accumulated depreciation and depletion						(0.2)
Net property, plant and equipment			10.9			11.0
Intangible assets, net						(0.7)
Investment in and advances to affiliates and joint ventures						1.9
Deferred income taxes			0.7			1.6
Other assets			0.7			0.8
Total noncurrent assets			12.3			14.6
Total Assets			7.9			8.7
Current liabilities:
Accounts payable			0.1			(1.8)
Accrued income taxes			(0.3)			1.0
Accrued liabilities			(1.1)
Total current liabilities			(1.3)			(0.8)
Noncurrent liabilities:
Long-term debt						(0.5)
Deferred compensation						0.3
Deferred income taxes			12.7			16.2
Other long-term liabilities						(1.2)
Total noncurrent liabilities			12.7			14.8
Shareholders' Equity:
Additional paid in capital			(0.2)
Retained earnings			(3.1)			(3.6)
Accumulated other comprehensive income (loss)			(0.1)			(0.2)
Total AMCOL shareholders' equity			(3.4)			(3.8)
Noncontrolling interest			(0.1)			(1.5)
Total equity			(3.5)			(5.3)
Total Liabilities and Shareholders' Equity			7.9			8.7
Tax [Member] | Adjustments [Member]
Current liabilities:
Accrued income taxes			(0.1)			1.2
Total current liabilities			(0.1)			1.2
Noncurrent liabilities:
Deferred income taxes						0.4
Total noncurrent liabilities						0.4
Shareholders' Equity:
Retained earnings			(0.1)			(1.6)
Total AMCOL shareholders' equity			(0.1)			(1.6)
Total equity			(0.1)			(1.6)
Other [Member] | Adjustments [Member]
Current assets:
Cash and cash equivalents						(0.5)
Accounts receivable, net			0.3			(2.4)
Inventories			(0.2)			(0.9)
Prepaid expenses						0.4
Other			(0.6)
Total current assets			(0.5)			(3.4)
Property, plant, equipment, and mineral rights and reserves:
Land						(0.7)
Depreciable assets			0.3			(2.1)
Gross property, plant and equipment			0.3			(2.8)
Less: accumulated depreciation and depletion						(0.2)
Net property, plant and equipment			0.3			(2.6)
Intangible assets, net						(0.7)
Investment in and advances to affiliates and joint ventures						1.9
Other assets						0.3
Total noncurrent assets			0.3			(1.1)
Total Assets			(0.2)			(4.5)
Current liabilities:
Accounts payable			0.1			(1.1)
Accrued income taxes			(0.2)			(0.1)
Accrued liabilities						(0.1)
Total current liabilities			(0.1)			(1.3)
Noncurrent liabilities:
Long-term debt						(0.5)
Deferred compensation						0.3
Deferred income taxes			0.1
Other long-term liabilities						(1.2)
Total noncurrent liabilities			0.1			(1.4)
Shareholders' Equity:
Retained earnings			0.1			(0.4)
Accumulated other comprehensive income (loss)			(0.3)			(0.1)
Total AMCOL shareholders' equity			(0.2)			(0.5)
Noncontrolling interest						(1.3)
Total equity			(0.2)			(1.8)
Total Liabilities and Shareholders' Equity			(0.2)			(4.5)
Spain [Member] | Adjustments [Member]
Current assets:
Accounts receivable, net			(1.6)			(0.4)
Inventories			(1.8)			(1.0)
Total current assets			(3.4)			(1.4)
Property, plant, equipment, and mineral rights and reserves:
Total Assets			(3.4)			(1.4)
Current liabilities:
Accrued income taxes			(0.3)			(0.1)
Accrued liabilities			(0.8)			0.1
Total current liabilities			(1.1)
Shareholders' Equity:
Retained earnings			(2.5)			(1.4)
Accumulated other comprehensive income (loss)			0.2
Total AMCOL shareholders' equity			(2.3)			(1.4)
Total equity			(2.3)			(1.4)
Total Liabilities and Shareholders' Equity			(3.4)			(1.4)
South Africa [Member] | Adjustments [Member]
Current assets:
Inventories			0.2
Total current assets			0.2
Property, plant, equipment, and mineral rights and reserves:
Mineral rights			10.6			13.6
Gross property, plant and equipment			10.6			13.6
Net property, plant and equipment			10.6			13.6
Deferred income taxes			0.7			1.6
Total noncurrent assets			11.3			15.2
Total Assets			11.5			15.2
Current liabilities:
Accounts payable
Accrued income taxes			0.1
Accrued liabilities
Total current liabilities			0.1
Noncurrent liabilities:
Deferred income taxes			12.6			15.8
Total noncurrent liabilities			12.6			15.8
Shareholders' Equity:
Additional paid in capital			(0.2)
Retained earnings			(0.9)			(0.3)
Accumulated other comprehensive income (loss)						(0.1)
Total AMCOL shareholders' equity			(1.1)			(0.4)
Noncontrolling interest			(0.1)			(0.2)
Total equity			(1.2)			(0.6)
Total Liabilities and Shareholders' Equity			11.5			15.2
Malaysia [Member]
Property, plant, equipment, and mineral rights and reserves:
Other assets						0.5
Total noncurrent assets						0.5
Malaysia [Member] | Adjustments [Member]
Current assets:
Accounts receivable, net			(0.7)			(1.1)
Total current assets						(1.1)
Property, plant, equipment, and mineral rights and reserves:
Total Assets						(0.6)
Current liabilities:
Accrued income taxes						(0.2)
Accrued liabilities			(0.3)
Total current liabilities			(0.3)			(0.2)
Shareholders' Equity:
Retained earnings			0.3			(0.4)
Total AMCOL shareholders' equity			0.3			(0.4)
Total equity			0.3			(0.4)
Total Liabilities and Shareholders' Equity						(0.6)
Dong Ming [Member] | Adjustments [Member]
Current liabilities:
Accounts payable						(0.7)
Accrued income taxes						0.2
Total current liabilities						(0.5)
Shareholders' Equity:
Retained earnings						0.5
Total AMCOL shareholders' equity						0.5
Total equity						$ 0.5