Goodwill and other intangible assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Other Intangible Assets [Member]	Dec. 31, 2011 Other Intangible Assets [Member]	Dec. 31, 2010 Other Intangible Assets [Member]	Dec. 31, 2012 Compx Furniture Components [Member]	Dec. 31, 2012 EWI [Member]	Dec. 31, 2009 Component Products Segment [Member]
Goodwill [Line Items]
Goodwill acquired through acquisition	$ 5.3	$ 6.4						$ 6.4	$ 10.1
Goodwill loss of discontinued operations		(14.3)					(14.3)
Consolidated gross goodwill	396.2	396.2
Other intangible assets	0.2	0.2	2.1
Net of accumulated amortization				3.8	3.8
Amortization of intangible assets related to continuing operations				$ 0.3	$ 0.5	$ 0.5