Condensed Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current assets:
Cash and cash equivalents	$ 16.8	$ 16.9	$ 23.7	$ 17.9	$ 21.2	$ 26.8	$ 27.7
Accounts receivable, net	217.2		204.8			190.1
Inventories	146.0		144.8			105.6
Prepaid expenses	19.2		15.7			13.0
Deferred income taxes	4.2		5.9			5.5
Income tax receivable	11.0		6.9			8.5
Other	4.0		6.1			6.2
Total current assets	418.4		407.9			355.7
Property, plant, equipment, and mineral rights and reserves:
Land	13.9		13.9			10.9
Mineral rights	49.8		52.5			65.0
Depreciable assets	507.8		482.6			452.3
Gross property, plant and equipment	571.5		549.0			528.2
Less: accumulated depreciation and depletion	291.4		275.5			256.7
Net property, plant and equipment	280.1		273.5			271.5
Goodwill	69.4		69.5			70.9
Intangible assets, net	35.8		36.6			41.9
Investment in and advances to affiliates and joint ventures	26.8		26.4			20.9
Available-for-sale securities	3.0		3.8			14.2
Deferred income taxes	9.0		8.5			9.2
Other assets	26.5		24.4			23.5
Total noncurrent assets	450.6		442.7			452.1
Total Assets	869.0		850.6			807.8
Current liabilities:
Accounts payable	50.3		56.5			51.4
Accrued income taxes	10.1		2.4			5.1
Accrued liabilities	58.3		57.9			55.2
Total current liabilities	118.7		116.8			111.7
Noncurrent liabilities:
Long-term debt	251.0		260.7			235.7
Pension liabilities	35.2		34.8			21.3
Deferred compensation	9.0		8.9			9.0
Deferred income taxes	12.9		13.5			16.6
Other long-term liabilities	19.3		19.2			18.4
Total noncurrent liabilities	327.4		337.1			301.0
Shareholders' Equity:
Common stock	0.3		0.3			0.3
Additional paid in capital	99.2		94.3			95.1
Retained earnings	339.7		316.4			279.6
Accumulated other comprehensive income (loss)	(18.8)		(15.0)			28.7
Less: Treasury stock	(1.3)		(3.4)			(8.9)
Total AMCOL shareholders' equity	419.1		392.6			394.8
Noncontrolling interest	3.8		4.1			0.3
Total equity	422.9		396.7	410.6		395.1
Total Liabilities and Shareholders' Equity	$ 869.0		$ 850.6			$ 807.8