Investment in Kronos Worldwide, Inc. - Additional Information (Detail) (Kronos, USD $) In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Kronos
Schedule Of Change In Carrying Value Of Equity Investment [Line Items]
Outstanding common stock, shares	35.2	35.2
Aggregate market value	$ 445.5	$ 458.6
Quoted market price per share	$ 12.65	$ 13.02

Balance held at close of period in number of shares.

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