Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income (loss)	$ 64.9	$ 58.5	$ 28.5
Other comprehensive income (loss) -
Pension adjustment	(0.9)	(13.5)	(0.4)
Tax benefit (expense)	0.8	5.0	0.2
Unrealized gain (loss) on interest rate swap agreement	0.6	(2.4)	(3.6)
Tax benefit (expense)	0	0.9	1.3
Unrealized gain (loss) on available-for-sale securities	10.8	(10.3)	(11.4)
Tax benefit (expense)	(1.2)	1.0	4.1
Foreign currency translation adjustment	5.2	(24.8)	7.5
Total other comprehensive income (loss)	15.3	(44.1)	(2.3)
Comprehensive income (loss)	80.2	14.4	26.2
AMCOL Shareholders [Member]
Net income (loss)	65.1	58.5	29.2
Other comprehensive income (loss) -
Pension adjustment	(0.9)	(13.5)	(0.4)
Tax benefit (expense)	0.8	5.0	0.2
Unrealized gain (loss) on interest rate swap agreement	0.6	(2.4)	(3.6)
Tax benefit (expense)	0	0.9	1.3
Unrealized gain (loss) on available-for-sale securities	10.8	(10.3)	(11.4)
Tax benefit (expense)	(1.2)	1.0	4.1
Foreign currency translation adjustment	5.4	(24.1)	6.5
Total other comprehensive income (loss)	15.5	(43.4)	(3.3)
Comprehensive income (loss)	80.6	15.1	25.9
Noncontrolling Interest [Member]
Net income (loss)	(0.2)	0	(0.7)
Other comprehensive income (loss) -
Pension adjustment	0	0	0
Tax benefit (expense)	0	0	0
Unrealized gain (loss) on interest rate swap agreement	0	0	0
Tax benefit (expense)	0	0	0
Unrealized gain (loss) on available-for-sale securities	0	0	0
Tax benefit (expense)	0	0	0
Foreign currency translation adjustment	(0.2)	(0.7)	1.0
Total other comprehensive income (loss)	(0.2)	(0.7)	1.0
Comprehensive income (loss)	$ (0.4)	$ (0.7)	$ 0.3