CORRECTION OF ERRORS IN PREVIOUSLY REPORTED FINANCIAL STATEMENTS, (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011		Mar. 31, 2011		Dec. 31, 2010
Current assets:
Cash and cash equivalents	$ 16.9	[1]	$ 24.1	[1],[2]	$ 21.2	[1]	$ 26.8	[1]
Accounts receivable, net	202.8	[1]	204.4	[1],[2]
Inventories	148.3	[1]	144.3	[1],[2]
Prepaid expenses	17.2	[1]	15.2	[1],[2]
Deferred income taxes	6.2	[1]	4.1	[1],[2]
Income tax receivable	5.7	[1]	8.2	[1],[2]
Other	4.6	[1]	6.1	[1],[2]
Total current assets	401.7	[1]	406.4	[1],[2]
Property, plant, equipment, and mineral rights and reserves:
Land	12.5	[1]	12.1	[1],[2]
Mineral rights	55.0	[1]	52.5	[1],[2]
Depreciable assets	502.5	[1]	484.7	[1],[2]
Gross property, plant and equipment	570.0	[1]	549.3	[1],[2]
Less: accumulated depreciation and depletion	285.2	[1]	275.7	[1],[2]
Net property, plant and equipment	284.8	[1]	273.6	[1],[2]
Goodwill	70.2	[1]	69.5	[1],[2]
Intangible assets, net	37.2	[1]	36.9	[1],[2]
Investment in and advances to affiliates and joint ventures	27.1	[1]	26.4	[1],[2]
Available-for-sale securities	2.9	[1]	3.8	[1],[2]
Deferred income taxes	9.3	[1]	8.1	[1],[2]
Other assets	25.6	[1]	24.4	[1],[2]
Total noncurrent assets	457.1	[1]	442.7	[1],[2]
Total Assets	858.8	[1]	849.1	[1],[2]
Current liabilities:
Accounts payable	47.7	[1]	56.5	[1],[2]
Accrued income taxes	6.5	[1]	2.3	[1],[2]
Accrued liabilities	57.7	[1]	59.2	[1],[2]
Total current liabilities	111.9	[1]	118.0	[1],[2]
Noncurrent liabilities:
Long-term debt	250.7	[1]	260.7	[1],[2]
Pension liabilities	34.6	[1]	34.8	[1],[2]
Deferred compensation	9.5	[1]	8.9	[1],[2]
Deferred income taxes	14.8	[1]	12.7	[1],[2]
Other long-term liabilities	19.5	[1]	19.1	[1],[2]
Total noncurrent liabilities	329.1	[1]	336.2	[1],[2]
Shareholders' Equity:
Common stock	0.3	[1]	0.3	[1],[2]
Additional paid in capital	97.6	[1]	94.3	[1],[2]
Retained earnings	321.9	[1]	314.3	[1],[2]
Accumulated other comprehensive income (loss)	(4.7)	[1]	(14.7)	[1],[2]
Less: Treasury stock	(1.7)	[1]	(3.4)	[1],[2]
Total AMCOL shareholders' equity	413.4	[1]	390.8	[1],[2]
Noncontrolling interest	4.4	[1]	4.1	[1],[2]
Total equity	417.8	[1]	400.2		399.2		400.5
Total Liabilities and Shareholders' Equity	858.8	[1]	849.1	[1],[2]
Previously reported [Member]
Current assets:
Cash and cash equivalents	16.9		23.7		21.2		27.3
Accounts receivable, net	204.0
Inventories	150.6
Prepaid expenses	17.2
Deferred income taxes	6.2
Income tax receivable	5.7
Other	4.6
Total current assets	405.2
Property, plant, equipment, and mineral rights and reserves:
Land	14.3
Mineral rights	43.8
Depreciable assets	500.2
Gross property, plant and equipment	558.3
Less: accumulated depreciation and depletion	285.1
Net property, plant and equipment	273.2
Goodwill	70.2
Intangible assets, net	36.9
Investment in and advances to affiliates and joint ventures	27.1
Available-for-sale securities	2.9
Deferred income taxes	8.6
Other assets	26.0
Total noncurrent assets	444.9
Total Assets	850.1
Current liabilities:
Accounts payable	47.7
Accrued income taxes	6.8
Accrued liabilities	57.0
Total current liabilities	111.5
Noncurrent liabilities:
Long-term debt	250.7
Pension liabilities	34.6
Deferred compensation	9.5
Deferred income taxes	1.5
Other long-term liabilities	19.5
Total noncurrent liabilities	315.8
Shareholders' Equity:
Common stock	0.3
Additional paid in capital	97.8
Retained earnings	326.6
Accumulated other comprehensive income (loss)	(4.7)
Less: Treasury stock	(1.7)
Total AMCOL shareholders' equity	418.3
Noncontrolling interest	4.5
Total equity	422.8
Total Liabilities and Shareholders' Equity	850.1
Adjustments [Member]
Current assets:
Cash and cash equivalents	0		0.4		0		(0.5)
Accounts receivable, net	(1.2)
Inventories	(2.3)
Total current assets	(3.5)
Property, plant, equipment, and mineral rights and reserves:
Land	(1.8)
Mineral rights	11.2
Depreciable assets	2.3
Gross property, plant and equipment	11.7
Less: accumulated depreciation and depletion	0.1
Net property, plant and equipment	11.6
Intangible assets, net	0.3
Deferred income taxes	0.7
Other assets	(0.4)
Total noncurrent assets	12.2
Total Assets	8.7
Current liabilities:
Accounts payable	0
Accrued income taxes	(0.3)
Accrued liabilities	0.7
Total current liabilities	0.4
Noncurrent liabilities:
Deferred income taxes	13.3
Total noncurrent liabilities	13.3
Shareholders' Equity:
Additional paid in capital	(0.2)
Retained earnings	(4.7)
Total AMCOL shareholders' equity	(4.9)
Noncontrolling interest	(0.1)
Total equity	(5.0)
Total Liabilities and Shareholders' Equity	8.7
Tax [Member] | Adjustments [Member]
Current assets:
Cash and cash equivalents	0
Total current assets	0
Property, plant, equipment, and mineral rights and reserves:
Gross property, plant and equipment	0
Net property, plant and equipment	0
Total noncurrent assets	0
Total Assets	0
Current liabilities:
Accounts payable	0
Accrued income taxes	(0.3)
Total current liabilities	(0.3)
Noncurrent liabilities:
Total noncurrent liabilities	0
Shareholders' Equity:
Retained earnings	0.3
Total AMCOL shareholders' equity	0.3
Total equity	0.3
Total Liabilities and Shareholders' Equity	0
Other [Member] | Adjustments [Member]
Current assets:
Cash and cash equivalents	0
Accounts receivable, net	(0.3)
Inventories	(0.3)
Prepaid expenses	0
Deferred income taxes	0
Income tax receivable	0
Other	0
Total current assets	(0.6)
Property, plant, equipment, and mineral rights and reserves:
Land	(1.8)
Mineral rights	0
Depreciable assets	2.3
Gross property, plant and equipment	0.5
Less: accumulated depreciation and depletion	0.1
Net property, plant and equipment	0.4
Intangible assets, net	0.3
Investment in and advances to affiliates and joint ventures	0
Available-for-sale securities	0
Deferred income taxes	0
Other assets	0
Total noncurrent assets	0.7
Total Assets	0.1
Current liabilities:
Accounts payable	0
Accrued income taxes	0.1
Accrued liabilities	0
Total current liabilities	0.1
Noncurrent liabilities:
Long-term debt	0
Pension liabilities	0
Deferred compensation	0
Deferred income taxes	0.1
Other long-term liabilities	0
Total noncurrent liabilities	0.1
Shareholders' Equity:
Common stock	0
Additional paid in capital	0
Retained earnings	0.1
Accumulated other comprehensive income (loss)	(0.2)
Less: Treasury stock	0
Total AMCOL shareholders' equity	(0.1)
Noncontrolling interest	0
Total equity	(0.1)
Total Liabilities and Shareholders' Equity	0.1
Spain [Member] | Adjustments [Member]
Current assets:
Cash and cash equivalents	0
Accounts receivable, net	(0.6)
Inventories	(2.3)
Total current assets	(2.9)
Property, plant, equipment, and mineral rights and reserves:
Gross property, plant and equipment	0
Net property, plant and equipment	0
Total noncurrent assets	0
Total Assets	(2.9)
Current liabilities:
Accounts payable	0
Accrued income taxes	(0.2)
Total current liabilities	(0.2)
Noncurrent liabilities:
Total noncurrent liabilities	0
Shareholders' Equity:
Retained earnings	(2.8)
Accumulated other comprehensive income (loss)	0.1
Total AMCOL shareholders' equity	(2.7)
Total equity	(2.7)
Total Liabilities and Shareholders' Equity	(2.9)
South Africa [Member] | Adjustments [Member]
Current assets:
Cash and cash equivalents	0
Inventories	0.3
Total current assets	0.3
Property, plant, equipment, and mineral rights and reserves:
Mineral rights	11.2
Gross property, plant and equipment	11.2
Net property, plant and equipment	11.2
Deferred income taxes	0.7
Total noncurrent assets	11.9
Total Assets	12.2
Current liabilities:
Accounts payable	0
Accrued income taxes	0.1
Total current liabilities	0.1
Noncurrent liabilities:
Deferred income taxes	13.2
Total noncurrent liabilities	13.2
Shareholders' Equity:
Additional paid in capital	(0.2)
Retained earnings	(0.8)
Total AMCOL shareholders' equity	(1.0)
Noncontrolling interest	(0.1)
Total equity	(1.1)
Total Liabilities and Shareholders' Equity	12.2
Poland [Member] | Adjustments [Member]
Current assets:
Cash and cash equivalents	0
Accounts receivable, net	(0.3)
Total current assets	(0.3)
Property, plant, equipment, and mineral rights and reserves:
Gross property, plant and equipment	0
Net property, plant and equipment	0
Other assets	(0.4)
Total noncurrent assets	(0.4)
Total Assets	(0.7)
Current liabilities:
Accounts payable	0
Accrued liabilities	0.7
Total current liabilities	0.7
Noncurrent liabilities:
Deferred income taxes	0
Total noncurrent liabilities	0
Shareholders' Equity:
Retained earnings	(1.5)
Accumulated other comprehensive income (loss)	0.1
Total AMCOL shareholders' equity	(1.4)
Total equity	(1.4)
Total Liabilities and Shareholders' Equity	$ (0.7)

[1] Restated

[2] Condensed from audited financial statements.