Employee Benefit Plans (Details 6) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Hedge Funds [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	$ 4.0	$ 3.9	$ 2.2
Fair Value Measurements Recurring [Member]
Fair value of pension plan assets
Fair value of pension plan assets	39.1	34.5
Fair Value Measurements Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	14.1	11.6
Fair Value Measurements Recurring [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	21.0	19.0
Fair Value Measurements Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	4.0	3.9
Fair Value Measurements Recurring [Member] \| Short Term Investment Funds [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0.6	0.7
Fair Value Measurements Recurring [Member] \| Short Term Investment Funds [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Short Term Investment Funds [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0.6	0.7
Fair Value Measurements Recurring [Member] \| Short Term Investment Funds [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| US Equity Securities [Member]
Fair value of pension plan assets
Fair value of pension plan assets	14.0	11.2
Fair Value Measurements Recurring [Member] \| US Equity Securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	1.4	0
Fair Value Measurements Recurring [Member] \| US Equity Securities [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	12.6	11.2
Fair Value Measurements Recurring [Member] \| US Equity Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| International Equity Securities [Member]
Fair value of pension plan assets
Fair value of pension plan assets	9.5	6.0
Fair Value Measurements Recurring [Member] \| International Equity Securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	4.5	2.0
Fair Value Measurements Recurring [Member] \| International Equity Securities [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	5.0	4.0
Fair Value Measurements Recurring [Member] \| International Equity Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| AMCOL International Common Stock [Member]
Fair value of pension plan assets
Fair value of pension plan assets	2.1	1.9
Fair Value Measurements Recurring [Member] \| AMCOL International Common Stock [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	2.1	1.9
Fair Value Measurements Recurring [Member] \| AMCOL International Common Stock [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| AMCOL International Common Stock [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Governmental Agencies [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0.7	1.0
Fair Value Measurements Recurring [Member] \| Governmental Agencies [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	1.0
Fair Value Measurements Recurring [Member] \| Governmental Agencies [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0.7	0
Fair Value Measurements Recurring [Member] \| Governmental Agencies [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Corporate Bonds [Member]
Fair value of pension plan assets
Fair value of pension plan assets	5.4	5.0
Fair Value Measurements Recurring [Member] \| Corporate Bonds [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	5.4	5.0
Fair Value Measurements Recurring [Member] \| Corporate Bonds [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Corporate Bonds [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Guaranteed Investment Contracts [Member]
Fair value of pension plan assets
Fair value of pension plan assets	1.3	2.5
Fair Value Measurements Recurring [Member] \| Guaranteed Investment Contracts [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Guaranteed Investment Contracts [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	1.3	2.5
Fair Value Measurements Recurring [Member] \| Guaranteed Investment Contracts [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Real Estate Index Funds [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0.8	0.6
Fair Value Measurements Recurring [Member] \| Real Estate Index Funds [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Real Estate Index Funds [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0.8	0.6
Fair Value Measurements Recurring [Member] \| Real Estate Index Funds [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Commodities Linked Funds [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0.7	1.7
Fair Value Measurements Recurring [Member] \| Commodities Linked Funds [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0.7	1.7
Fair Value Measurements Recurring [Member] \| Commodities Linked Funds [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Commodities Linked Funds [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Hedge Funds [Member]
Fair value of pension plan assets
Fair value of pension plan assets	4.0	3.9
Fair Value Measurements Recurring [Member] \| Hedge Funds [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Hedge Funds [Member] \| Significant Observable Inputs (Level 2) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	0	0
Fair Value Measurements Recurring [Member] \| Hedge Funds [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair value of pension plan assets
Fair value of pension plan assets	$ 4.0	$ 3.9

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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