Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net income (loss)	$ 12.9	$ 12.2
Other comprehensive income (loss):
Foreign currency translation adjustment	10.9	1.9
Unrealized gain (loss) on available-for-sale securities, net of tax	(0.9)	(2.9)
Unrealized gain (loss) on interest rate swap agreements, net of tax	0.2	0.5
Pension adjustments, net of tax	0.2
Comprehensive income (loss)	23.3	11.7
AMCOL Shareholders [Member]
Net income (loss)	12.8	12.2
Other comprehensive income (loss):
Foreign currency translation adjustment	10.7	1.9
Unrealized gain (loss) on available-for-sale securities, net of tax	(0.9)	(2.9)
Unrealized gain (loss) on interest rate swap agreements, net of tax	0.2	0.5
Pension adjustments, net of tax	0.2
Comprehensive income (loss)	23.0	11.7
Noncontrolling Interest [Member]
Net income (loss)	0.1
Other comprehensive income (loss):
Foreign currency translation adjustment	0.2
Unrealized gain (loss) on available-for-sale securities, net of tax
Unrealized gain (loss) on interest rate swap agreements, net of tax
Pension adjustments, net of tax
Comprehensive income (loss)	$ 0.3