Business segment information - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Mar. 31, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Direct controlling interest in subsidiary	50.00%		50.00%
Indirect controlling interest in subsidiary	30.00%		30.00%
Proceeds from patent litigation settlement		$ 7.5		$ 7.5
Impairment charge for assets held for sale	0.4		0.4	1.1
Reversal of accrued contingent consideration	0.8		0.8
NL Industries Inc [Member]
Segment Reporting Information [Line Items]
Total controlling interest	83.00%		83.00%
Proceeds from patent litigation settlement		$ 7.5