The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 159

-Paragraph 18

-Subparagraph f

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 18

-Paragraph 20

-Subparagraph a (1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Other assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended				3 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2011	Dec. 31, 2012 Byron Center facility [Member]	Sep. 30, 2012 Byron Center facility [Member]	Dec. 31, 2012 LPC [Member]	Dec. 31, 2012 Basic Management, Inc. [Member]	Dec. 31, 2012 Landwell [Member]	Dec. 31, 2012 Basic Management Inc And Landwell [Member]
Other Assets Non Current [Line Items]
Purchase of TiO2 from the plant							52.00%
Percentage of additional ownership interest of BMI in Landwell								32.00%	12.00%	50.00%
Asset held for sale write-downs	$ 0.8	$ 1.1	$ 0.5	$ 0.9		$ 0.2
Net proceeds of sale	3.6				3.6
Loss on sale	$ 1.5	$ (0.9)	$ (1.8)		$ 0.8