Marketable Securities - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Recognized pre-tax loss related to aggregate net change in market value	$ (35,645)	$ (55,911)
Valhi Inc \| Common stock
Schedule Of Available For Sale Securities [Line Items]
Number of shares owned	14.4	14.4	14.4
Quoted marked price per share	$ 2.28	$ 2.28	$ 6.17
Recognized pre-tax loss related to aggregate net change in market value		$ 55,900

Balance held at close of period in number of shares.

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