Investment in Kronos Worldwide, Inc. - Additional Information (Detail) - Kronos - USD ($) $ / shares in Units, shares in Millions, $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Schedule Of Equity Method Investments [Line Items]
Number of shares owned	35.2	35.2
Aggregate market value	$ 493.8	$ 405.7
Quoted market price per share	$ 14.02	$ 11.52

Balance held at close of period in number of shares.

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