Noncontrolling Interest (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Change from net income and transfers from noncontrolling interest
Net income attributable to AMCOL shareholders	$ 12.8	$ 12.2
Transfers from noncontrolling interest:
Decrease in additional paid-in capital for purchase of the remaining noncontrolling interest in South Africa (Proprietary) Limited		(5.7)
AMCOL Shareholders [Member]
Change from net income and transfers from noncontrolling interest
Net income attributable to AMCOL shareholders	12.8	12.2
Transfers from noncontrolling interest:
Decrease in additional paid-in capital for purchase of the remaining noncontrolling interest in South Africa (Proprietary) Limited		(5.2)
Decrease in additional paid-in capital for transfer of 26% interest in Batlhako		(3.4)
Change from net income attributable to AMCOL shareholders and transfers from noncontrolling interest	$ 12.8	$ 3.6