Noncontrolling Interest (Details) (USD $) In Millions, 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
Change from net income and transfers from noncontrolling interest
Net income attributable to AMCOL shareholders	$ 21.6	$ 13.2	$ 13.2	$ 13.3	$ 34.8	$ 26.5	$ 59.6	$ 28.9	$ 33.2
Transfers from noncontrolling interest:
Purchase of noncontrolling interest						(5.7)
AMCOL Shareholders [Member]
Change from net income and transfers from noncontrolling interest
Net income attributable to AMCOL shareholders					34.8	26.5
Transfers from noncontrolling interest:
Purchase of noncontrolling interest						(5.4)
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					$ 34.8	$ 17.7