Long-term debt - Additional Information (Detail) In Millions, unless otherwise specified	1 Months Ended		3 Months Ended		6 Months Ended	9 Months Ended				12 Months Ended	9 Months Ended		12 Months Ended			9 Months Ended					9 Months Ended					3 Months Ended	9 Months Ended		9 Months Ended
	Sep. 30, 2012 USD ($)	Sep. 30, 2012 CAD	Mar. 31, 2011 USD ($)	Mar. 31, 2011 EUR (€)	Jun. 30, 2012 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2012 EUR (€)	Sep. 30, 2011 USD ($)	Sep. 30, 2011 EUR (€)	Dec. 31, 2011 EUR (€)	Sep. 30, 2011 6.5% Senior Secured Notes [Member] USD ($)	Sep. 30, 2011 6.5% Senior Secured Notes [Member] EUR (€)	Dec. 31, 2011 6.5% Senior Secured Notes [Member] USD ($)	Dec. 31, 2011 6.5% Senior Secured Notes [Member] EUR (€)	Jun. 13, 2012 6.5% Senior Secured Notes [Member] EUR (€)	Sep. 30, 2012 Maturity Extension Date [Member]	Sep. 30, 2012 Minimum [Member] EUR (€)	Sep. 30, 2012 Maximum [Member] EUR (€)	Sep. 30, 2012 Letter of Credit [Member] CAD	Sep. 30, 2012 Revolving credit facility [Member] USD ($)	Sep. 30, 2012 Revolving Credit Facilities [Member] Minimum [Member]	Sep. 30, 2012 Revolving Credit Facilities [Member] Maximum [Member]	Sep. 30, 2012 Kronos [Member] USD ($)	Sep. 30, 2012 Kronos [Member] Revolving credit facility [Member] USD ($)	Sep. 30, 2012 NL Industries Inc [Member] USD ($)	Mar. 31, 2012 CompX [Member] USD ($)	Sep. 30, 2012 CompX [Member] USD ($)	Sep. 30, 2012 Canada [Member] CAD	Sep. 30, 2012 Canada [Member] Kronos [Member]
Line of Credit Facility [Line Items]
Term loan	$ 400.0					$ 400.0																	$ 389.3
Interest rate of senior secured notes	6.50%	6.50%	6.50%	6.50%		6.50%	6.50%			6.50%
Principal amount outstanding															279.2
Percentage of term loan issued	98.50%	98.50%				98.50%	98.50%
Additional term loan borrowings	100					100
Minimum LIBOR rate for Kronos Option						1.00%	1.00%
Variable rate on LIBOR for term loan						4.75%	4.75%
Variable Rate on Base Rate for term loan						3.75%	3.75%
Average interest rate on revolving bank credit facility	5.82%	5.82%				5.75%	5.75%																				3.60%
Principal repayments						5.0
Extended maturity date						October 2013	October 2013									September 2017							June 2018	June 2017
Common stock of certain of Kronos U.S. wholly-owned subsidiaries/Common stock or other ownership interest of Kronos Canadian subsidiary																							100.00%						65.00%
Unsecured promissory note issued by Kronos wholly-owned subsidiary																							362.1
Specified financial covenant (leverage to EBITDA)						3.5 to 1.0	3.5 to 1.0
Provision for other indebtedness	50					50
Carrying amount of term loan includes unamortized original issue discount	5.7					5.7
Principal amount of notes			115.7	80.0					40.8	40.8	57.6	40.6	57.6	40.6
6.5% Senior secured notes				400.0
Term loan sufficient to pay principal, call premium			102.17%	102.17%		1.01083%	1.01083%
Call premium of senior long term notes			2.5			(6.2)		(2.5)
Pre tax charge on redemption of senior long term notes			3.3		7.2
Principal amount of notes									30.4
Net gain redemption of senior Notes								0.1
Borrowing availability																			25					125
Availability of letters of credit	15.0					15.0
Variable rate on LIBOR for revolving credit facility, Minimum						1.50%	1.50%
Variable rate on LIBOR for revolving credit facility, Maximum						2.00%	2.00%
Variable Rate on Base Rate for revolving credit facility, Minimum						0.50%	0.50%
Variable Rate on Base Rate for revolving credit facility, Maximum						1.00%	1.00%
Fixed charge coverage ratio, Range Start						1.0	1.0
Fixed charge coverage ratio, Range End						1.0	1.0
Amount available for borrowing																				125
Increase the maximum borrowing																	80	120
Interest rate on outstanding borrowings																					1.50	1.90
Borrowings under credit facility						107.4	80.0
Average interest rate on revolving bank credit facility	1.63%	1.63%				1.63%	1.63%																				3.30%
Credit facility repaid an aggregate							45
Credit facility when repaid	56.2					56.2
Average interest rate	1.86%	1.86%				1.86%	1.86%
Letters of credit outstanding		7.5
Availability Outstanding letters of credit																												10.0
Repayment of Promissory Notes																									$ 3.9	$ 1.0	$ 1.8
Interest rate for promissory note																									3.25%		1.50%
Interest rate for promissory note																									325.00%		1.50%