Commitments and contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012 Cases Plaintiff site	Dec. 31, 2011
Commitments And Contingent Liabilities [Line Items]
Receivables from recoveries	$ 0	$ 0
Estimate Cost	1.6
Number of sites	50
Not currently able to estimate a range of costs	5
Type of cases pending	1,125
Number of plaintiffs involved	1,995
Number of plaintiffs have been administratively dismissed or placed on the inactive docket	8,075
NL Industries Inc [Member]
Commitments And Contingent Liabilities [Line Items]
Number of cases settled and dismissed and found not liable	100
Period by which loss contingency claims settled and dismissed	20 years
Estimate Cost	49.0
Estimate Costs	$ 79